JPL S P 43.7

MICROBIOLOGICAL ASPECTS OF CLEAN ROOM TECHNOLOGY

AS APPLIED TO SURGERY -with special reference to

unidirectional airflow systems

Jet Propulsion Laboratory California Institute of Technology

Pasadena, California 91 103

(SASA-CR-14C 176) H I C R O B I O L O G X C A L A S P E C T S OF ZLZAN RCCH TECHNOLOGY AS APPLIED TO SURGERY, WITH S P E C I A L REFERENCE TO UNIDI i3ECTIONAL AIRFLOJ SYSTEMS (Je t Propulsicn L a b . ) 88 p H C 5 7 . 5 6 C S C L 36E

Unclas G3/34 4946C

Prepared for

Applications Technology Office NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

https://ntrs.nasa.gov/search.jsp?R=19740026445 2020-03-26T17:41:06+00:00Z

MICROBIOLOGICAL ASPECTS OF CLEAN ROOM TECHNOLOGY

AS APPLIED TO SURGERY -with special reference to

unidirectional airflow systems

Michael D. Wardle

Jet Propulsion Laboratory California Institute of Technology

Pasadena, California 91 103

July 9, 1974

Prepared for

Applications Technology Office NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

PREFACE

This work presents the results of one phase of research carried

out at the Jet Propulsion Laboratory, California Institute of Technology,

under Contract NAS 7-100, sponsored by the National Aeronautics and

Space Administration' s Applications Technology Office.

iii

CONTENTS

SUMMARY AND OVERALL CONCLUSIONS . . . . . . . . . . . . . . . . .

I. I N T R O D U C T I O N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11. CLEAN ROOM TECHNOLOGY . . . . . . . . . . . . . . . . . . . . . . A. CLASSES O F CLEAN ROOMS . . . . . . . . . . . . . . . . . . B. HIGH EFFICIENCY PARTICULATE AIR FILTERS . . . . C. UNIDIRECTIONAL AIRFLOW . . . . . . . . . . . . . . . . . . D. T Y P E S O F U A F SYSTEMS . . . . . . . . . . . . . . . . . . . .

1. Ver t i ca l U A F R o o m s . . . . . . . . . . . . . . . . . . . . 2. V e r t i c a l U A F Tunnels . . . . . . . . . . . . . . . . . . . 3. V e r t i c a l Wal l -Less UAF . . . . . . . . . . . . . . . . . 4. Horizonta l UAF Rooms . . . . . . . . . . . . . . . . . . 5. Hor izon ta l UAF Tunnels . . . . . . . . . . . . . . . . . . 6 . Horizonta l Wall- L e s s UAF . . . . . . . . . . . . . . . .

E. NONUNIDIRECTIONAL AIRFLOW CLEAN ROOMS . . . .

111. MICROBIOJAGICAL MONITORING O F THE SURGICAL CLEAN ROOM ENVIRONMENT . . . . . . . . . . . . . . . . . . . . A. VOLUMETRIC SAMPLING O F AIRBORNE

MICROORGANISMS . . . . . . . . . . . . . . . . . . . . . . . . . B. FALLOUT AND SURFACE MICROBIOLOGICAL

SAMPLING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . .

IV. E F F E C T O F CLEAN AIR SYSTEMS ON T H E ENVIRONMENTAL MICROBIOLOGY O F T H E OPERATINGROOM ............................ A. OPERATING ROOM ENVIRONMENTAL

M I C R O B I O L O G Y . . . . . . . . . . . . . . . . . . . . . . . . . . .

1. Non-Clean Room Envi ronments . . . . . . . . . . . . . 2. C l e a n R o o m E n v i r o n m e n t a ......,.,...... .

CONTENTS (contd)

B. SOURCES O F AIRBORNE MICROBIAL CONTAMINATTON IN CLEAN ROOM OPERATING EiJVIRONMENTS .................

C. CLEAN ROOMS AND IMPROVED SURGICAL A P P A R E L .......................

D. E F F E C T O F CLEAN ROOM AIRFLOW CONFIGURATION ON WOUND SITE CONTAMINATION ..........................

E. CONCLUSIONS ............................ ...... V. CLEAN ROOMS AND SURGICAL WOUND INFECTION

A. SURGICAL WOUND INFECTIONS ................ 1. Definition ........................... 2. F a c t o r s Involved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. S o u r c e s 4. Statistics. ...........................

..... B. AIRBORNE INFECTION O F SURGICAL WOUNDS.

............................... 1. P r o ............................... 2. Con

C. ENDOGENOUS I N F E C T I O N . . .........*........ D. INFLUENCE O F CLEAN ROOMS ON ....... SURGICALLY INDUCED WOUND INFECTION.

1. Orthopedic r and Clean Rooms .............. ....... 2. A m e r i c a n College of Surgeons S ta tement

E. CONCLUSIONS ............................

BIBLIOGRAPHY (NOT CITED) . . . . . . . . . . . . . . . . . . . . . TABLES

1 . A i r c leanl iness c l a s s e s ...................... T h e effect of reduced a i r b o r n e m i c r o b i a l ....... l eve l s dur ing s u r g e r y on wound infect ion r a t e ,

FIGURES

1 . 2 .

CONTENTS (contd)

................ Particle size distribution curves

Vertical unidirectional airflow room ............. ............. Vertical unidirectional airflow tunnel

........ Vertical wall-less unidirectional airflow unit

............ Horizontal unidirectional airflow room

........... Horizontal unidirectional airflow tunnel

Horizontal wall-less unidirectional airflow unit ...... Horizontal unidirectional airflow wall-le s s module ................................. Nonunidirectional airflow clean room .............

vii

ABSTRACT

The microbiological aspects of clean room technology a s

applied to surgery were reviewed. The following pertinent subject

a reas were examined: (1) clean room technology per s e and its

utilization for surgery, ( 2 ) microbiological monitoring of the clean

room surgical environment, (3) clean rooms and their impact on

operating room environmental microbiology, and (4) the effect of

the technology on surgical wound infection rates. Conclusions

were drawn for each topic investigated.

SUMMARY AND OVERALL CONCLUSIONS

In i ts formulation and initial applications, clean room technology was

aimed a t controlling nonbiological environmental parameters. The demon-

stration of the clean room1 s value for the control of viable contamination in

NASA programs and its merit in the reduction of postoperative wound infec-

tion rates a s interpreted from European studies provided the basic impetus

for the transfer of the technology to the operating room. The transfer has,

to date, not seen the development of a standard that i s definitive with respect

to the microbial control afforded by clean rooms in the surgical context,

Therefore, the environmental control provided by surgical clean rooms i s

often described per existing standards relating to the control of nonviable

particulates. However, the surgeon employing this technology i s not con-

cerned about nonviable particulates (as were i ts originators and many of i ts

present day practitioners), but, rather, he i s interested in the environmental

microbiologic control it affords and the effect of such on wound infection.

In line with the objective of microbiological control, the use of HEPA

filtration, efficient at the submicron level, may not be necessary in light of

data that indicate the preponderance of airborne surgical wound infection

producing particles can probably be removed from incoming operating room

a i r by fi l ters efficient in the retention of la rger size particles.

Human beings, rather than the air-handling system, account for the

major contribution of microbial contamination in the modern operating room.

Recent studies of surgical apparel systems, cited a s effective microbial

barr iers , tend to indicate the feasibility of the rigid control of human source

microorganisms in the operating room, a s a technique capable of enhancing

the clean room technology approach to reducing microbial contamination of

the surgical wound.

There exists a great danger in total reliance on clean rooms for en-

vironmental microbiologic control; they cannot be depended on to compen-

sate totally for improperly applied o r faulty aseptic technique. Clean rooms,

be they turbulent o r unidirectional flow, a r e not in themselves the final

solution to problems of control of the operating room1 r microbiological en-

vironment, For maximum benefit, technology applied towards this goal murt

be tailored to i t r rurgical ure. Rererrch in thir area i r not complete and

efforts should be continued to define the most meaningful, effective and

economical method8 for regulating the microbial environment of the opera-

ting room.

It will require a large, controlled study to directly evaluate, in a

statistically significant manner, t1 t effect of the clean room on the incidence

of postoperative surgical wound infection. However, pertinent data do exist

that point to the value of a reduced level of operating room airborne micro-

bial contamination in lowering the incidence of wound infection far certain

surgical situations.

DEFINITION O F TERMS

The following te rms a r e used throughout this document and therefore

require special attention a s to definition:

CLEAN ROOM An enclosed area employing control over

(defined per Federal the particulate matter in a i r with tempera-

Standard 209 B (1973)) ture, humidity, and pressure control, a s

required; with a particle count not to exceed

a total of 100,000 particles per cubic foot

(approximately 3500 per l i te r ) of a size

0. 5 pm and larger , o r 700 particles per

cubic foot (approximately 25 per l i te r ) of

a size 5.0 p m and larger .

CLEAN AIR Air issued directly from a HEPA filter

(see page 9 ) .

The clean roome under discussion employ HEPA filtration, hence the

te rms clean room and clean a i r will be used interchangeably. Other t e rms

a r e defined a s they appear in the text.

SECTION I

INTRODUCTION

It has been estimated that one of every 13 surgical patient^ :. I:: * a

postoperative wound infection (National Academy of Sciences-: :.tional

Research Council 1964) and that the cost of these infections runs into the

billions of dollars pe r year (General Accounting Office 1972). In the eixeies,

unidirectional airflow (UAF-also referred to a s "laminar") was introduced

in t f~ the hospital operating room as a means of reducing the incidence of

post-operative wound infection. Since that time, a controversy has been

growing over whether clean a i r ( i . e. , a i r supplied via high efficiency par-

ticulate a i r (HEPA) fi l ters) in general, and U A F in particular, is in fact

effective in reducing such infections.

Infect ion control a ims a t identifying and evaluating factors that give

r i s e to infection. Microbial contamination of the wound during surgery has

been proposed a s an event that, for certain surgical procedures, can lead

to a postoperative wound infection. The following three pr imary sources of

surgical wound microbial contamination can impact the operative stage:

(a) contact: Microorganisms a r e introduced into the w a n d through direct

contact by the physicians, instruments, etc, ; (b) endogenous: The patient's

own microflora invade the wound; and (c) airborne: Microorganisms a r e

deposited in the wound a s a result of an inadequate air-handling system o r

contaminating events in the operating room, Contact and airborne contami-

nation a r e generally considered in t e rms of exogenous microorganisms, i. e . , those not native to the patient. Traditional measures have been developed

for guarding against al l of these modes of wound contamination; however,

the recent interest in clean roomm for surgical application has emphasized the

need for further evaluation of the role of airborne microorganisms in

surgically induced wound infections. The specific purpnse of employing

rlean room technology in surgery i s to control airborne contamination.

The move toward clean room surgery in America war, more precisely,

a move toward unidirectional flow clean a i r . The UAF clean room was f i r s t

described in 1962 (Whiffield 1962). It wag initially ured for surgery in

January of 1966 a t Bataan Memorial Hospital (NASA 1971). A recent survey

of hospitals employing clean room facilities found that the number has grown

f rom 23 in 1970 to well over 300 in 1972 (anonymous 1972). This survey

included only surgical, in-hospital, o r full-room (portable roomr, included)

patient ca r e facilities. Portable UAF isolation beds were not enumerated;

it was found that a vast majority of the recc,.-ded facilities employed UAF.

It will be the a im of this document to carefully review the status of

clean room technology in surgery f rom the basics of the technology to its

value in the reduction of postoperative wound infection ra tes attributable to

microbial contamination of the surgical wound dur ing the operation. Owing

to the prevailing interest in the UAF method of supplying clean a i r , emphasis

will be placed on this aspect of the technology.

Although i t is recognized that clean room technology ip employed

in the hope of controlling infections other than thore surgically induced,

e, g., for the treatment of burn patients and immunologically deficient t r an r -

plant and cancer patients, i t i r the a im of thir document to confine the d i r -

currion to i t s application to surgery.

I t i s a lso to be noted that this document has restr icted i ts defi*.' t i of

clean a i r to that supplied by HEPA filtration. This should not be to imply that s imilar results in t e rms of microbial a i r quality cann , , achieved

by alternate means (e. g. , other filtration methods, surgical isol, rs, ultra-

violet irradiation, and chemical treatment) . The present discussion will be

styled to provide meaningful interpretation for other methods capable of

reducing microbial contamination in the operating room s i r t o levels com-

parable to the subject clean rooms.

SECTION I1

CLEAN ROOM TECHNOLOGY

A. CLASSES OF CLEAN ROOMS

Severa l c l a s s e s of clean rooms a r e general ly recognized, i. e . ,

C l a s s e s 100, 10,000, o r 100,000 a s defined by Federa l Standard 20QB (1973).

(For a discussion of how F e d e r a l Standard 209B di f fers f r o m i t s p redecessor ,

209A, s e e G a r s t 1973. ) Fed .a1 Standard 209B makes reference only to the

par t icula te control p a r a m e t e r s to be expected and not to des i rable microbia l

control conditions: It recognizes that a i rhorne microorganisms a r e p a r t i -

cula tes and a s such a r e reflected in the total par t icula te count of the different

a i r cleanliness c l a s ses . F i g u r e 1 shows the pa r t i c l e s i ze distribution curves

(with m e t r i c equivalents; a s defined by 209B f~ r the th ree c l a s s e s of clean

rooms. The curves indicate average par t ic le s i z e distributions that ex i s t

in the a i r . A Claas 100 environn~ent i s one containing a maximum of 100 3 pa r t i c l e s of 0. 5 - ) ~ m diameter and l a r g e r p e r f t (3.514). Class !0,000

environments have up t o 10,000 pa r t i c l e s (35f'li) of th is s i ze range and

s imi la r ly for C lass 100,000. These curves a r e plotted semilogari thmical ly,

with the total number of pa r t i c l e s p e r cubic foot ( l i t e r ) expressed logari thmi-

cally. As a n exar-ple, f o r the C!aes 100 curve where the X-intercept is just

before the 5 - ) ~ m s ize , the par t ic le reading i s 1 p e r cubic foot (0.035/i) ,

n3t 0. Were the curve to be sxt-apolated, one would expect the re to b e a

finite, but low, frequency of occurrence of l a r g e r pa r t i c l e s (e. g. , 25, 50,

and 100 pm).

Reference to performance of these r o o m s in t e r m 8 of microbiologic

control can be found in National Aeronautics and Space Administration

(NASA) document NHB 5340.2 (NASA 1967). Table 1 shows the s tandards

fo r microbia l cleanliness s e t by this document (surface contamination levele

a r e for horizontal surfaces) . The NASA Standards document was developed

a s a d i r e c t exteneion of F e d e r a l Standard 209, to provide for definition8 and

degrees o; microbiological environmental coutrol in consonance with the

United Sta tes policy ( see Hall and Lyle 1971 ) f o r controlling the spread of

t e r r e s t r i a l microorganisms to planets of biological in teres t by unmanned

PARTICLE SIZE ( p m)

4- COUNTS BELOW 10 (0.35) PARTICES/FT~ (LITER) ARE UNRELIABLE EXCEPT WHEN A LARGE NUMBER OF SAMPLINGS IS TAKEN

Fig. 1 . Particle size distribution curves (Federal Standard 209B 1973)

Table 1. Air c l e a n h e s s c lasses (from NASA 1967)

Class English system (metric sy s tern)

100 (3.5)

10,000 (350)

100,000 (3,500)

Average numbe r of viable

2 particles /ft / week

(per m 2

per week)

Maximum number of

particles/ft3 0 .5 pm

and la rger (per l i t e r )

*Counts below 10 (0. 35) particles/ft3 ( l i t e r ) a r e unreliable except when a large number of samples is taken.

exploratory spacecraft. Recently, the American Society for Testing and

Materials (ASTM) has been working to develop procedures for the assess -

ment of microbiological contamination in clean rooms (anonymous 197 2).

Maximum number of

/ft3 5~

and larger (per l i t e r )

B. HIGH EFFICIENCY PARTICULATE AIR (HEPA) FILTERS

Many types of clean rooms exist ( see below); however, they usually

have one feature in common - the use of high efficiency particulate a i r

Maximum number of

viable particleslft

(per l i t e r )

(HEPA) fi l ters to provide to a work station a i r that i s low in both particulate

and microbial content. The HEPA filter is described a s follows by NASA

document SP-5076 (NASA 1969): "The HEPA f i l ter uses a media of d ry

ultrafine f ibers (usually l e s s than 1 pm ia diameter) , which may be 100%

glass fiber o r a combination of glass and asbestos fibers. This media i s

formed in a thin porous sheet which i s pleated o r fan-folded to form pockets,

with separators interleaved between the folds to prevent i ts collapse and to

render the maximum a r e a for a i r filtering. . . . The media/separator config-

uration is assembled in a rigid frame. The media surfaceu and edges adja-

cent t o the interior eidee of the f rame a r e sealed and bocded to the f rame with

adhesive. The f i l te r f r a m e may be made f rom (a ) plain resin-glued plywood,

(b) f i r e retardant- type plywood, o r ( c ) meta l , e i ther s teel o r aluminum, with

hard nonflaking o r nonscaling finish. The depth of the pockets o r folds in the

media and the s i ze of the f r a m e determine the f i l te r media a r e a and the

airf low capacity of the f i l te r assembly. A standard s i ze f i l te r assembly,

24 x 24 x 5-718 in. (6 1 x 6 1 x 15 c m ) , will provide a minimum airflow

capacity of 500 ft3 (14, 158 1 ) lmin . " The HEPA f i l te r i s defined in 209B a s :

''A f i l te r a s specified in Mil-F-5 lo68 with a minimum efficiency of 99. 97'7'0

a s determined by tes t . The t e s t can be by the homogenous dioctylphthalate

(DOP) method o r other equally sensitive method a t a n airflow of 100'7'0 of the

rated flow capacity for a l l s i ze f i l te rs and a t 20'70 of the rated airf low for

s izes 4, 5, and 6." The DOP fog t e s t provides for a minimum efficiency

es t imate of 99.97% for pa r t i c l es r 0. 3 pm. Leaks in HEPA f i l te r banks can

occur in the f i l te r medium itself, a t the interface of the f i l ter medium with

the support f r ame , the f r a m e i tself , and a t the interface of the support

f r a m e with the clean room wall. Therefore , i t i s imperat ive that HEPA

fi l ter banks be judiciously monitored fo r leaks and, for those interested in

the microbial control they provide, that microbiological monitoring be

conducted in addition to physical testing (Goddard 1963, I rons 1967, Songer

1963). To prolong the life of HEPA f i l t e r s (nominally 10 to 15 y r ) , p re f i l t e r s

a r e used to capture g r o s s part iculates. Their efficiency, a s determined ky

the NBS Discoloration (Dust Spot) T e s t ( see Federa l Standard 209B 1973),

v a r i e s f rom 20-30'7'0 for initial p re f i l t e r s to 80-90'70 fo r intermediate

pref i l te rs .

C. UNIDIRECTIONAL AIRFLOW (UAF)

Clean (HEPA-filtered) a i r can be provided to a n operating room in a

multitude of ways. Unidirectional airflow is one mode, and m u s t be defined

a t th is point in o r d e r that i t may be distinguished f r o m other clean a i r

sys tems.

The unidirectional airf low clean room i s often r e f e r r e d to a s a l aminar

airf low system. Federa l Standard 209B (1973) states that, fo r purposes of

the Standard, laminar airf low s t a l l be defined as : "airflow in which the

en t i r e body of a i r within a confined a r e a essential ly moves with uniform

velocity along parallel flow lines. In recent years the t e r m "laminar" has

been judged to be somewhat of a misnomer when used with reference to a

surgical application. The a i r does not proceed in a truly laminar configura-

tion, even in the absence of obstructing objects in i ts path; i t moves, in the

absence of obstructions, in a minimal-turbulence, unidirectional fashion.

Instances of turbulence and reverse flow of a i r can occur in work a r e a s

supplied with this type of airflow; however, for purposes of simplicity and

discussion no attempt will be made to develop additional nomenclature to

denote these systems and the t e rm unidirectional airflow (UAF) will be used

throughout this document.

D. TYPES OF UAF SYSTEMS

1. Vertical UAF Rooms

The vertical UAF room (Fig. 2) employs HEPA-filtered o ir that

flows vertically f rom a filter bank located in the ceiling, down through the

room, and out a grated o r perforated floor. Beneath the floor i s a se t of

prefi l ters through which the a i r passes into an exhaust plenum and, by

means of blowers, i s recirculated through the HEPA f i l ters and into the

room. Thesc rooms a r e commonly capable of tight temperature and

humidity control. The HEPA filter-supply plenum system may be arranged

in another way, with HEPA-filtered a i r being supplied from a remote si te

to the ceiling and through a diffuser system into the room. However, such

a modified system should be checked out for homogenous airflow of adequate

velocity pe r the recommendation of 209B that an airflow velocity of 90 * 18 f t /

min (27. 5 * 5 .5 m/min ) be maintained throughout the unoccupied enclosure

of a UAF system. The vertical UAF room provides good control over con-

tamination to a r eas adjacent to a contaminating event because such airborne

contamination is rapidly carr ied down and out of the room with minimum

chance of lateral spread. Properly utilized, i t easily provides a Class 100

environment.

The 1972 census of ultraclean hospital facilities (anonymous 1972)

did not list any full room vertical UAF systems. Probably, the reason they

have yet to be employed is that they a r e expensive and their permanent

nature res t r ic ts the use of the room in which they a r e placed.

DUCT PREFILTER --I RETURN DUCT

Fig. 2. Vertical unidirectional airflow room (after NASA 1967)

2. Vertical UAF Tunnels

Often eferred to a s "greenhouse" units, these systems (Fig. 3)

a r e s imilar to the art ical UAF rooms. They differ in that they use movable

rigid plastic o r nonstatic plastic curtain sidewalls, open loop intake and

exhaust (100% of intake a i r i s f rom the ambient surroundings and 100% of

exhaust i s to ambient), and a solid floor, and a r e , in some cases , portable.

Temperature and humidity of the unit a r e governed by the surrounding room.

These tunnels provide for a clean room within a room. The lack of a grated

o r perforated floor to provide for a closed loop a i r recirculation requires

that the sidewall edge be held sufficiently high off the floor to allow for

adequate airflow out of the enclosure. This in turn requires that any cri t ical

work station be high enough above the sidewall edge to be under UAF con-

ditions and at minimum r isk of contamination f rom a possible ambient a i r

migration. As applied to surgery, v e r f ~ c a l UAF tunnel systems present a

problem in te rms of location of surqical lights. It i s preferable that lights

be situated so a s to be nonobstructive to the airflow emanating f rom the

fi l ter bank. These units a r e increasingly seen in surgical applications and

have often been used in the space program to provide Class 100 conditions

for spacecraft that would be difficult to manipulate in a stationary, rigid wall

vert ical flow room.

3. Vertical Wall-Less UAF

A vertical wall-less UAF enclosure (Allander 1968) is shown in

Fig. 4. An outer a i r curtain, formed from a rectangular slotted delivery

system in the ceiling, passes HEPA-filtered a i r downward and outward f rom

the inner working a r ea a t a velocity of approximately 10.7 m/min. The

inner a r e a s a r e supplied with HEPA-filtered a i r that passes through the

enclosure a t approximately 7.6 mlmin. The wall-less systems have seen

limited acceptance in surgery.

4. Horizontal UAF Rooms

These rooms (Fig. 5) a r e essentially identical to the vertical

UAF rooms except fo r the configuration of airflow. The environment at any

FLOOR --/

Fig. 3. Vertical unidirectional airflow tunnel (after NASA 1967)

HEPA FILTERS -CEILING

AIR FLOW

/-- FLOOR

Fig. 4. Vertical wall-less unidirectional airflow unit

r RETURN DUCT -7 - BLOWER

1 HEPA FILTERS

PREFILTER - FLOOR

Fig. 5 . Horizontal unidirectional airflow room (after NASA 1967)

locale in this room is dependent on activities a t work stations between it and

the incoming HEPA-filtered a i r . F i r s t work locations (those neares t the

HEPA f i l ters) generally meet Class 100 conditions. The a i r velocity

requirements for these rooms, depending on their length, a r e often greater

than the nominal 27 .5 * 5 . 5 m/min (see NASP ' , . 9). Obstructions on the

ceiling of these units (e. g. , surgical lights ) can lead to undesirable turbu-

lence and interference with the room's cleandown capability. The design of

these rooms (length grea te r than width) usually calls for fewer HEPA fi l ters,

fewer supporting s t ructures , and l e s s equipment than the vert ical rooms.

A few of these rooms a r e presently in use; however, many more a r e planned

for new hospitals (Agnew 1972).

5. Horizontal UAF Tunnels

The horizontal UAF tunnel (Fig. 6 ) , except for direction of

airflow, is similar to the vertical UAF tunnel unit. I ts sidewalls and ceiling

a r e often made of plastic for easy assembly and disassembly. As with the

vert ical tunnels, the horizontal tunnels can provide Class 100 environments

a s "rooms within rooms, " and a r e subject to the prevailing temperature and

relative humidity of the surrounding room. These tunnels a r e a lso subject

to the res t ra ints noted for the horizontal UAF rooms and a r e comparable in

effectiveness to them. They a r e among the most economical of UAF room-

s ize enclosure:;.^ and a r e therefore popular for surgical use.

6. Horizontal Wall-Less UAF

Horizontal wall-less UAF units a r e available in a variety of

sizes. The full size units (Fig. 7 ) typically consist of a 1 .8 to 2 . 4 m HEPA

fil ter bank that supplies a i r to the surgical wound site. The "first a i r" of

these units can supply Class 100 conditions (Ritter e t al. 1973). Airflow

velocities (36.6 to 4 2 . 7 mlmin ) a r e somewhat higher than for other systems.

This type of unit represents a large fraction of the UAF operating room

systems currently in use (Agnew 1972). A small version horizontal UAF

wall-less module i s shown in Fig. 8. Such units a r e employed to provide

clean a i r directly to the wound site.

FIRM OR RIGID CEILING AND WALLS

BLOWER

I

/ / HEPA FILTERS

-

Fig. 6 . Horizontal unidirectional airflow tunnel (after NASA 1969)

PROJECTOR VANES -

Fig. 7. Horizontal wall-lee8 unidirectional airflow unit (top view)

4' BLOWER

HEFA FILTER

Fig. 8. Horizontal unidirectional airflow wall-lee s module

E . NONUNIDIRECTIONAL AlRFLOW CLEAN ROOMS

Federa l Standard 209B r e f e r s to a nonunidirectional (nonlaminar) flow

clean room o r work station a s being "supplied with fi?tered a i r with no

specified requirement for uniform airflow pat terns of uniform a i r velocity. " The non-UAF room, often r e f e r r e d to a s the ttconventionaltt clean room,

furnishes HEPA-filtered a i r to a work a r e a but in a turbulent manner

(Fig. 9). In addition, the number of a i r changes p e r *lour (15-20)

i s much l e s s than for the UAF faci l i t ies (200 to 500). Compared to UAF

facilities, the t ime required to remove generated contamination in these

rooms i s much longer. F i l tered and conditioned a i r is typica.11~ supplied to

the room through ceili.:: diffusers and exhausted through re tu rn ducts

qituated near the floor around the room periphery. These rooms a r e not

considered capable of meeting C l a s s 100 require men,^ under opera:ing

conditions, but under res t r ic t ive use can achieve Class 100,000 and, in

scrne instances, C lass 10,000.

F. CONCLUSIONS

Clean r o o m technology was developed p r imar i ly a s a means of con-

trolling the concentration of a i rborne part iculates. The part iculate nature of

a i rborne microorganisms renders them amenable to regulation by application

of this technology; however, existing s tandards a r e nor definitive with respect

to the microbial control afforded by clean roome in the surgical context.

In t e r m s of nonviable part iculates, the nonunidi rec t ion~l flow clean

room cannot achieve the levels of cleanliness achievable by unidirectional

flow sys tems. However, the control of nonviable8 has l i t t le meaning in the

apldication of clean room technology to surgery ,

Fig. 9. Nonunidirectional airflow clean room (after NASA 196 9 )

SECTION I11

MICROBIOLOGICAL MONITORING O F THE SURGICAL CLEAN ROOM ENVIRONMENT

The des i re to minimize the number of microbes in operating room a i r

has necessitated the development o h p p r o p r i a t e microbiological monitoring

techniques. The efficiency of clean a i r operating rooms i s pr imari ly

measured by their effect on the level of environmental microbes. This

section discusses methods of microbiological monitoring in the operating

room and how su=h methods relate to the special case of the clean room

environment in surgery.

There i s no presently known sampling technique that will yield es t i -

mates of the numbers of al l viable microbes present in an environment. - The detection of viable microbes i s dependent on the media, growth tempera-

ture, relative humidity, etc. , employed in the sampling technique. There-

fore, the results of the microbiological monitoring of an environment must

be considered relative rather than absolute. The key word in operating

room microbial sampling i s viable, for the enumeration of microbes by

methods that do not distinguish between viable and nonviable cells [e. g. , direct microscopic counting, light-scattering methods, and t r ace r

techniques ) i s of questionable usefulness in monitoring for organisms

capable of producing infection.

Modern microbiology encompas s e s the study of bacteria, fungi,

viruses, algae, and protozoa. The t e rm "microbiological, " a s applied to

environmental sampling in the operating room, i s usually defined to include

only bacteria and fungi.

A. VOLUMETRIC SAMPLING O F AIRBORNE MICROORGANISMS

In the course of evaluating operating room environments, much atten-

tion has been directed to determining the number of microorganisms p e r

unit volume of intramural a i r . An intense interest in the microbiological

contamination of operating room a i r was fostered during the 1950's by a r i s e

in the number of antibiotic-resistant staphylococcal infections and concern

over control of their dissemination.

Microbiological aerosols a r e compossd of particulates ranging in

s ize from less than 1 pm to approximately 50 pm ( o r in some cases la rger )

(Wolf et al. 1959). The particles may represent single organisms o r clumps

composed of many cells. Usually, organisms exist in aerosol form attached

to la rger nonviable particles o r as free-floating forms surrounded by dried

organic o r inorganic matter. Vegetative cells a r e generally present (in

a reas of low human activity) in lower concentrations than spores owing to

their sensitivity to drying and other deleterious factors inherent in the

airborne state. Vegetative cells a r e m a r e prevalent in wound infection

than a r e spores. Staphylococci, streptococci, and tubercle bacilli a r e

quite resistant to the inimical effects of the airborne state and hence a;e

commonly cited as the prevalent dis ease-producing organisms dissemi-

nated by airborne routes. The sampling of microbiological aerosols can

provide a number of different types of informatian, e. g., the total number

of viable organisms, a particular fraction of the total population present

( t h r o u ~ h the use of selective media), and the number and/or the size dis-

tribution of particles bearing viable cells. To an investigator seeking a

finer resolution in his environmental sampling, i t is important to choose

a media selective for a particular organism o r supplemented with growth

factors essential for the proliferation of cells injured in the sampling

process ( see Kingston 1971 for a review of this subject).

The purpose of this discussion will be to provide insight into some

common approaches for microSiological a i r sampling in the hospital operating

room. Air sampling methods and devices will not be comprehensively

referenced; for such a treatment, see Wolf e t al. 1959 and the American

Conference of Governmental Industrial Hygienists 1972 (includes commercial

sources).

Volumetric sampling involves collecting a sample of the ambient

environment by means of a sampler operating on a vacuum principle. This

technique leads to a sampling bias in favor of small part icles, which a r e

readily captured by the sampler a i r s t r eam (Sehmel 1970). In ordinary

practice the e r r o r introduced by this factor is small; however, for sampling

in unidirectional flow environments, the need to redlice this bias i s more

critical. The best approach in such environments ia to utilize isokinetic

.ampling, i. e . , sampling that adjusta the velocity of the sampler airstr1:am

to equal that of the unidirectional flow airs t ream. Such adjustment is mo t

readily accomplished by modifying the sampler orifice to a size thibt will

permit isokinetic flow and situating i t so that i t faces head-on into the

ambient a i rs t ream.

The basic methods for volumetric sampling of airborne microbes

include (1) impaction on solid surfaces, ( 2 ) filtration, (3) centrifugation,

(4) impingement in liquids, and (5) electrostatic precipitation. These same

methods a r e basically those used to sample airborne nonviable particles;

the difference is the addition of a growth medium (e. g., the impingement

o r impaction menstruum), to provide for enumeration of viable micro-

organisms. The methods most popular for use in the operating room have

been impaction on solid surfaces and filtration.

Most impactor samplers a r e designed to detect the number of viable

particles pe r unit volume of a i r . This number i s to be distinguished from

the number of viable organisms; most viable particles a r e associated with

more than one viable cell. The most popular impactor samplers used in

sampling operating room environments a r e the sl i t (e. g . , Reyniers (no

longer commercially available)) and sieve (e. g . , Andersen) samplers.

These samplers require a ~ a c u u m source and a r e normally calibrated and 3 operated to sample a t 1 f t (28. 3P)lmin.

The s l i t sampler pulls a determined volume of a i r through a narrow

sli t placed a t a cri t ical standoff distance f rom the surface of an agar-filled

petr i dish. The sampler i s equipped with a timing mechanism that rotates

the agar surface, thereby providing a time correlation with detected con-

tamination. The steady rotation of the plate presents a f resh agar surface

in line with the incoming a i r s t ream, thus guarding against media desiccation

and permitting long sampling intervals before safnples a r e changed (com-

monly 1 to 2 h). Goldberg and Shechmeister (1951) evaluated factors affecting

the recovery of viable particles with a slit sampler (Bourdillon). They found

that slit-to-agar distance, slit width, and a i r velocity interact in the

determination of sampling efficiency. It is commonly stated that the main

cause of loss in sampling efficiency of the slit sampler is the h,,rmiul effect

on cell integrity of the ahove-mentioned critical sampling parameters.

The Andersen sampler (Andersen 1958) consists of a ser ies of six

sieve type samplers which have holes of progressively smaller diametr- ir

each succeeding plate after the initial a i r inlet. Beneath each plate is a

petri dish contcziuing agar. The velocity of the a i r impacting the agal

increases for each succeeding plate (stage) resulting in a separation of

viable particles into six size ranges a s foilows:

Stage Particle size (pm)

8.2 and larger

5.0 - 10.4

3.0 - 6.0

2.0 - 3.5

1.0 - 2.c

to 1.0

Thus the samplei provides for a correlation of colony count with particle

size range.

Filtration sampling in the operating room i s most commonly accom-

plished using membrane filters. The membrane filter sampler i s unique

among filtration sampling techniques in that organisms c ollec-red can be

enumerated in situ, i. e . , viable particles do not have to be removed from -- the filter material in the assay procedure. Therefore, the membrane

sampler eliminates one step in the assay protocol that could reduce the

viable count (Wolochow 1958) o r introduce contamination. Owing to the

severe desiccatmg action of the airflow through the filter medium, this i s

not the best method for recovering vegetative cells. F o r certain applica-

tions gelatin matrix membrane fi l ters may provide an increased recovery of

vegetative cells a s comparc d to cellulose membrane filters.

L e s s commonly used methods of volumetric sampling in the operating

room include s a m p l e r s which employ centrifugal force for propulsion of

microbia l pa r t i c l e s to a collecting surface (usually a g a r ) and liquid impinge-

ment sample r s . The Wells sample r i s an example of a centrifugal type

sampler . I t col lects microbial par t ic les on the walls of a broth- o r a g a r -

filled g lass cylinder, which i s then incubated and counted. The a l l -g lass

impinger (AGI) is pe rhaps the bes t known of the liquid impingers. Besides

i t s select ivi ty fo r pa r t i c l e s g r e a t e r than 15 to 17 pm, the instrument provides

optimal r e su l t s only when shor t sampling t imes a r e used; usually 1 nlin - a t

m o s t 10. Therefore , i t i s a mos t inconvenient ins t rument to u s e in the

operating room since i t must frequently be replaced with one carry ing

f r e s h media. In addition, the sample r equ i res fu r the r processing, which

entai ls dilutions and plating. The smal l sampling volume (usually 12. 5 l / m i n )

makes the AGI l e s s appealing for sampling unidirectional flow environments.

Methods of microbial sampling in the ope rating room that rely on

e lec t ros ta t ic precipitation have been avoided because of the safety haza rds

inherent in the handling of high voltages and the resultant e lec t r ica l ly

charged surfaces .

B. FALLOUT AND SURFACE MICROBIOLOGICAL SAMPLING

The s imples t method of sampling a i rborne contamination in the opera t -

ing room i s to m e a s u r e the number of viable pa r t i c l e s settling out of the

environment onto pe t r i dishes filled with nutr ient aga r . This technique

favors the detection of the l a r g e r par t ic les . F o r example, in stil l a i r a

4-pm par t ic le se t t les a t 2. 9 c m / m i n , but a 20-pm par t ic le se t t les a t

73. 2 c m / m i n (Wolf e t a l . (1959) - includes values fo r o ther s i ze pa r t i c l e s . )

Of course , the a i r movement in the t e s t environment will have an influence

on par t ic le settling. However, the a g a r fallout technique for a s sess ing the

number of viable par t ic les in the operating room environment is s tated by

many invest igators to b e representa t ive of wound s i t e contamination. This

assumption i s not ent i re ly valid s ince t h e r e a r e some obvious d i s s imi la r i t i e s

between an a g a r su r face and a surgical wound, e . g . , the wound i s concave in

shape and has a number of surface i r r egu la r i t i e s , and suction is often applied

to drain the wound. It must be r e m e m b e r e d that the fallout method m e a s u r e s

only viable par t ic les and, to formulate an es t ima te of viable organisms, a

technique to break up c l u s t e r s of organisms and dislodge microbes f rom

iner t part iculate ma t t e r mus t be incorporated.

An a l ternate and l e s s commonly used method of sedimentation sampling

is the fallout s t r ip technique. Tkls technique ut i l izes smal l s t r i p s (e . g . ,

s tainless s t ee l ) exposed to the environment for a specified period of t ime.

At the end of the esposure period the s t r i p s a r e assayed fo r the number of

microorganisms accumulated on them. This procedure has been commonly

employed by NASA for monitoring the microbiological environment of space-

craf t assembly a r e a s and has resulted in i t s incorporation into a NASA

standard (NASA 1968). The NASA vers ion ca l l s for the removal of mic robes

f rom s t r i p s by scnication; the resultant counts approximate the number of

viable o rgan i sms . Fallout s t r i p s favor the collection of spores a s cpposed

to vegetative f o r m s because of the unfavorable conditions present , cuch a s

desiccation and mate r i a l effects.

The two mos t commonly used methods fo r a s sess ing surface microbia l

contamination in the operating room a r e by swab and agar contact. The

swab-rinse technique involves the movement of a moistened cotton swab

over a surface s o a s to remove mic robes f rom a defined a r e a . The swab

head i s then broken off, dropped into a tube of diluent, and t rea ted (e. g . , by

agitation o r sonication) to remove mic robes entrapped in the cotton. Appro-

p r i a t e s e r i a l dilutions a r e performed and the a s s a y i s completed using the

pour plate method. The swab-r inse technique has been described a s having

a poor recovery efficiency (Angelotti e t a l . 1964), s ince it is affected by the

chemical and physical proper t ies of the sampled surfaces a s they re la t e to

the r e m ~ v a l of microbial par t ic les ; by the act ions of the person taking the

swab sample (the speed and p r e s s u r e of swabbing will v a r y with the s a m e o r

different individuals); and by the a s s a y procedure, which i s usually unable to

remove a l l of the organisms entrapped in the cotton.

The a g a r contact method i s a quick and e a s y technique for a s sess ing

surface microbial contamination in the operating room. The basic technique

consis ts of press ing a nutrient a g a r surface against the surface for which a

microbia l population es t ima te i s des i red , incubating the plate a t a specified

t empera tu re and humidity, and counting the colony-forming units. The m o s t

common fo rm of this sampling method is the RODAC plate (Hall. and Hartnet t

1964). It i s most effective f o r smooth, f lat sur faces . Since dilution i s not

possible, the technique i s o d y applicable to su r faces wi4'1 relat ively low

contamination levels . Angelotti e t a l . (1964) found this method to have low

accuracy but high prec is ion in a s sess ing surface contamination. Agar con-

tac t plate r e su l t s r ep resen t numbers of viable par t ic les .

Surface contamination can a l so be determined by imnlers ion methods.

Imnlersion in a diluent followed by shaking o r ul trasonic t rea tment and a

pour plate a s s a y i s useful in determining total numbers of viable cel ls .

Puleo e t al . (1967) have shown ultrasonic energy t o be m o r e effective in

breaking up bacter ia cell aggregates than mechanical agitation. The a fo re -

mentioned s ta in less s teel fallout s t r i p s a r e assayed by the immers ion

technique. Another fo rm of immers ion i s the d i rec t overlay of a surface

with nutr ient a g a r followed by incubation and counting. This method i s

usually restric+-.d by the s i ze compatibility of the t e s t surface and the a g a r

holding vesse l and, s ince dilution cannot be invoked, i s unsuitable for highly

contaminated surfaces . A technique for an in s i tu a s s a y of su r faces by a g a r -- spraying has been described (Hughes e t a l . 1968).

A recently developed method of microbiological surface sampling i s

the vacuum probe. This device was originally developed a t Sandia Labora-

t o r i e s (Dugan 1967). A vacuum source i s used to pull a i r into an or i f ice tip

that is placed close to the surface to be sampled. A high a i r velocity i s

established a t the t ip-surface juncture that d is rupts the boundary l a y e r of

a i r a t the surface and d raws mic robes p resen t on the surface into the a i r -

s t r e a m entering the tip. The a i r s t r e a m entering the sample r i s directed

onto a membrane f i l ter which along with the t ip and f i l ter housing i s assayed

by a n immersion-sonicat ion technique. Pe te r son and Bond (1969) have

evaluated a n aluminum vers ion of the probe and found it 98% efficient ir.

removal and 88% efficient in recovery of the surface organisms deposited

f r o m a i r . Improved design vacuum probes have been reported by

F a r m e r e t al . (1971) and Phil l ips and Pace (1972).

In the hospital environment perhaps the mos t cr i t ica l problem in

a s sess ing surface contamination i s that of residual germicides . Therefore ,

techniques aimed a t such a n a s s e s s m e n t should incorporate, if appropr ia te ,

agents to neutral ize residual germicides . Quite often, negative samples ? r e

interpreted a s indicating a surface is f r e e of microbial contamination when

in actuality such samples originate f rom the t r ans fe r of a germicide f rom

the surface to the growth medium, resulting in a bacter ios ta t ic o r bacter ic i -

dal effect. F a v e r o e t a l . (1968a) have accumulated a l i s t of neut ra l izers

for common germicides .

C. CONCLUSIONS

Microbiological monitoring of :he clean room surgica l environment

r equ i res unique considerations. These a r e m ~ s t apparent in the application

of monitoring techniques to unidirectional flow environments, where a e r o -

dynamics has a significant effect on the acquisition of a representa t ive

sample . Since the function of UAF sys tems is to prevent random d i spe r sa l

of microbial contaminants, only locales of in te res t should be selected a s

sampling s i t e s . In addition, i t should be kept in mind that , for m o s t a i r

sampling techniques, only a smal l fract ion of the l a rge volume of a i r p r e -

sented to the sampling s i te by UAF is actually sampled. F i ld !v , the

sensitivity of the sampling technique m u s t be honestly evaluated in the con-

text of i t s application. A statement on contamination levels in a clean room

surgica l environment i s warranted only in light of r e su l t s f rom proper con-

t ro l samples. Depending on the complexity of the technique, a portion of the

samples will be contaminated in the a s s a y procedure r a the r than a s a function

of environmental exposure.

SECTION IV

E F F E C T O F CLEAN AIR SYSTEMS ON THE ENVIRONMENTAL MICROBIOLOGY O F THE OPERATING ROOM

Clean a i r (HEPA-fi l tered) has been defined in Section 11-B a s a i r

f i l tered to a minimum of a 99.97% efficiency for the removal of par t icula tes

0. 3 (rm and l a r g e r . Such a definition does not, however, distinguish between

viable and nonviable part iculates. In t e r m s of i t s application to su rge ry ,

the main at tr ibute of clean a i r i s that i t contains a low number of viable

pa r t i c l e s p e r unit volume. In actual prac t ice , the levels of contamination

in a clean room a r e not absolute but relat ive, and depend on the interaction

of the clean room s y s t e m per s e and the par t icular mode of i t s utilization. -- Statements a s to the level of microbial contamination a t a s i te within a

clean room a r e highly dependent on the monitoring techniques enlployed ( see

Section 111). F e d e r a l Standard 209B (1973) and NASA Standards NHB 5340.2

(NASA 1967) and NHB 5340.1A (NASA 1968) have provided ae rospace m i c r o -

biologists with guidelines in the application of clean room technology to the

control of spacecraf t microbiological contamination. The ro te application

of these s tandards t o clean room technology a s used for s u r g e r y i s highly

questionable. NASA Standard 5340.2 specifies tkat Class 100 a i r shall have

no m o r e than 0.0035 viable part icles/ l and C l a s s 10,000, 0,0176/1, What

meaning do these f igures hold in the operating room? It 1s impossible to

s ta te a p r io r i the acceptable level of microbia l contamination in a n operating -- room. A l a r g e number of s tudies have been co , .~a~: ted to define such con-

tamination levels . In some instances a t tempts have been made t o co r re la t e

them with the incidence of postoperative wound infection - the ul t imate fac-

t o r in establishment of operating room a i r quality s tandards. A discussion

of the impact of clean room technology on wound infection will be presented

in Section V. The p resen t section will s e t the s tage fo r that diacuasion by

reviewing s o m e of the m o r e pertinent data concerning the effect of clean

room technology on the environmental microbiology of the operating room.

Discussion of the microbiology of clean r o o m s p e r s e will not be - attempted here. Rather , thz emphasis will be on data that provides a d i rec t

t ie with surgical applications of clean room technology. The following

r e fe rences provide a good data base on the microbiology of clean rooms:

Reakley e t al. 1966, Cown and Kethley 1967, Favero e t al. 1966,

Finkelstein 1965, Gavin e t al. 1969, Gehrke-Manning 1969, Goddard 1963,

Irons 1967, Kapell e t al. 1966, Lindell and G a r s t 1969, McDade e t al. 1965,

Paik e t al. 1966, Paik and S te rn 1968, P o r t n e r e t al. 1965, Powers 1965.

A. OPERATING ROOM ENVIRONMENTAL MICROBIOLOGY

This section presents some representa t ive studies of the environ-

mental microbiology of non-clean room (conventional) and clean room

surgical environments.

1. Non-Clean Room Environments

Much of the surgica l community evaluates microbial contami2a-

tion levels in the operating room i n t e r m s of the work of Bourdillon and

Colebrook (1946) which h a s been res ta ted by Girdlestone and Bourdillon

(1951) a s follows: "For the total numbcr of a i rborne par t ic les car ry ing

organisms which grow to visible colonies af ter 24 h on blood agar at 37"C,

af ter sampling during per iods of quiet operation, the f igures suggested were

a s follows: ( 1 ) for rooms used for dress ing s m a l l wounds o r for minor

operations only, 20/f t3 (0. 71 / P ) , ( 2 ) for theaters used for ordinary major

operat ions, 1 0/f t3 (0. 3511 ), and ( 3 ) for theaters used for long opera t io~ i s on

eas i ly infected t i ssues , 2.0-0.1 /f t3 (O.O7-O.O04/P ). The lower counts can

only be maintained by taking pains and spending money on ventilation plants. '!

Greene e t al. (1962) performed an evaluation of the environmental

microbiology of hospital a i r over a 15-mo period and foux~d a mean count

of 10.5 colonies/f t3 (0.3719 ) in the operating room, with a representa t ive

variat ion a s g r e a t a s 1 to 24 over a relat ively shor t t ime span ( c i r c a 1 h ) ,

Sampling was conducted using Casel la and Andersen volumetric s a m p l e r s

to alleviate the bias introduced against s m a l l pa r t i c l e s when sampling i s

conducted using sedimentation plates. The following table shows the

qualitative r e su l t s reported by these workers for i so la tes recovered from

operating rooms:

Number of i so la te s 1887

G r a m -positive cocci Hemolytic Nonhemolytic

Gram-posit ive rods Gram-negative rode Other bacter ia Penici l l in-resistant bacter ia Molds Yeasts Actinomycete s

Ford e t al. (1967) observed bacter ia l counts ranging f rom 15 to

18. 3/f t3 (0.53 to 0.651P) during surgica l act ivi t ies and determined that the

contamination levels were in d i rec t corre la t ion with the amount of human

activity. Identification of the environmental i so la tes showed the major i ty to

be traditional nonpathogens, with Staphylococcus epidermidis a s the predomi-

nating organism. Although p resen t in low numbers, S. aureus was found in

84.696 of the samples (3987 clean c a s e s were performed with 71 (2.41%)

giving r i s e to infection; 31 of these infections (43.7%) resulted from S. aureus

and 5 (7Oh) f rom S. epidermidis) .

2. Clean Room Environments

Favero e t al. (1968b) performed a study that compared types and

levels of mic robes in hospital operating rooms with thosc f0ur.d in industr ial

clean rooms. The highest levels of a i rborne microbia l contamination were

detected in the hospital operating rooms, and the lowest were observed in a

C l a s s 100 hcrizontal unidirectional flow clean room. The i r quantitative

r e su l t s w e t e a s follows:

Room Average number of

C l a s s of viab!e par t ic les / f t3 a r e a (pe r l i t e r )

Operating Room A::: - - - 10.7 (0.38)

Operating Room B - - - 9.8 (0. 35)

Clean R o o r ~ A 100, 000:::::: 5.3 - 6.0 (0.19 - 0.21)

:>Operating rooms f rom two different hospitals. $:;::Per Federa l Standard 209.

--- - -.-- ---- - Average number of

C lass of viable par t ic les / f t3 a r e a (per l i t e r ) -1

Clean Room B

Clean Room C

Clean R o o n ~ D

:::;::Per Federa l Standard 209 :::::::::Per U. S. Air F o r c e Technical O r d e r 00-25-203.

An examination of the types of mic roorgan i sms showed the hospital o ~ e r a t i n g

rooms to contain a higher percentage of microbes associated with dust and

soil ( spore f o r m e r s , fungi, and act inomycctes) than those commonly of

human origin (staphylococci, micrococci , corynebacterium-brevibacterium,

and streptococci) . The previously cited work of Greene e t al. (1962) found

the opposite to be t rue with r e spec t to hotipital operating rooms, i. e . , that

the majori ty of i so la tes were of human, r a the r than dust and soi l orgin.

The studies of Favero e t al. indicated the value cf clean room tecnnology in

the operating room fo r reducing a i rborne contamination. These workers

proper ly pointed out, however, that thc control afforded by clean roo..l

technology (especial ly unidirectional flow s y s t e m s ) i s mos t meaningfully

measured at the surgica l wound s i t e and that the t rue express ion of any

improvement in the quality of operating room a i r must be evidenced in

controlled studies of postoperative infection ra t e s .

Michaelsen e t al. (1967) found that conventional c lean r o o m s typically

yielded contamination levels some one o r d e r of magnitude lower than found

in hospital operating rooms and that approximately 7570 of the contaminants

w e r e human-source species. In addition, they noted that the unidirectional

downflow room could improve by s e v e r a l o r d e r s o i magnitude the levels of

contamination found in the bes t conventional clean rooms.

Whitfield (196d) r e l a t e s e a r l y studies of h is pioneer ve r t i ca l unidirec-

tional flow room that showed levels of contamination significantly lower than

i n modern surgica l facilit ies. Initial testing of h i s room to define i t s

capability i n reducing a i rborne contamination showed the following resul t s :

Ambient a i r -- Unidirectional flow

(1) Average number of 12 < O . 02 colonies/f t3 (0.42) (<O,OCb7) (per l i t e r )

Unidirectional flow -

(2) Average number of colonies/sct t l ing plate

(3 ) Average number of colonieslf t2 (per m2) ( impress ion plate)

Blowers off Blowers on

T e s t s of the ve r t i ca l unidirectional flow room a s used for su rge ry and com-

pared to a conventional operating room yielded the following resul t s :

Colonies / C t 3

(per l i t e r ) Colonies /settling plate

Vert ical Unidirectional F l ~ w 0.5 (0.018)

Conventional Operating Room 14. 4 (0.51)

A cr i t ica l factor in the a s s e s s m e n t of contamination levels in 3 unidi-

rect ional flow operating room i s the s i te at which samples a r e take^.

Because the airflow in these rooms functions to seques ter and remove con-.

tamination, thereby preventing i t s l a t e ra l spread, the averaging of containi-

nation a t different s i t e s o r the discussion of contamination a t other than the

c r i t i ca l s i t e (i. e . , the surgica l wound) clouds the interpretat ion of the degree

of contamination control afforded by a unidirectional flow sys tem (Cown and

Kethley 1967, Favero e t al. 1968b, Fox and Baldwin 1968). Baldwin e t al.

(1965) i n the i r study of the environmental microbiology of the wound r i t e

during neurosurgery in a conventional operating room found an average of

2 o rgan i sms / f t3 (0.071E) of a i r . These worker r note that, to their knowledge,

the i r monitoring (c i r ca 1964) was the f i r s t documented instance wherein

"bacterial a i r samplers were moved from their traditional location a t the

periphery of the room to the steri le field over the wound. It

Coriell e t al. (1968) studied a vertical unidirectional flow room and

found that, during general surgery, the use of the clean a i r system provided

for a marked reduction i n airborne microbial contamination levels (e. g.,

from 4.4 to 0.4 colony-forming units/ft3 (0.16 to 0.014lP ) during a bilateral

varicose vein ligation) a t the wound site. These workers consistently found

higher counts in the operative field (wound site) than a t other locales i n the

operating room and determined that the activation of the clean a i r system

could render the a i r vir+ually f ree of microbial contamination within 2 to

3 min.

McDade e t al. (1968) reported on the "Whitfield roomtt a s used a t

Bataan Memorial Hospital in Albuquerque, N. M. during assorted surgeries.

Their data on wound site contamination show levels of 0 to 0.2 viable

particles/ft3 (0 to 0,007/9 ) during aortic bifurcation resection and 0 to <l (0 to< O.O35/P), for pleural biopsy. Organisms recovered in the unidirec-

tional flow room were primarily those commonly associated with humans

and compared qualitatively (but not quantitatively) with those recovered

during inguinal herniorrhaphy i n a conventional operating room.

Charnley (1972), using vertical unidirectional flow and a filtration sys-

tem efficient to the 1-2 pm level, achieved wound site contamination lev2ls of

0 to 0.05 colonies/ft2/min (0 to 0. 5/m2/rnin) and 0. 1 colonies/ft3 (0.004/l)

during total hip replacement surgery.

During mock neurosurgical proceriures, Fox (1969), studying the con-

t rol of microbial contamination afforded by a horizontal unidirectional flow

system, found that the levels of wound site contamination varied from 0.02

to 0.05 organisms/ft3 (0.0007 to 0.00211 ) of a i r sampled as compared with

levels of 0.1 to 2 organisms /ft3 (0.004 to 0.071 P l i n a conventional operating

room.

Cook and Boyd (1971), using a modified unidirectional airflow module

that directed a horizontal flow of a i r over the wound, achieved significant

reductions in the number of bacteria settling at the operating site during a

se r ies of miscellaneous operations (1 1.2 bacter ia l ft2/rnin (1 21 /m2/min)

The predominant organism type recovered from the operating site was

coagulacre-negative rtaphylococcu~ (75% with the airflow unit verrur 79%

without).

Anspach and Bakers (1973), also using a modular unidirectional flow

unit, were able to significantly reduce the level of airborne bacteria a t the

wound (I. 0 to 0. 12/ft3 (0.035 to 0.00411 ) as measured by an q a r impact

sampler: 12.5 to 0. 83/ft3 (0.44 to 0.029/P) using a broth sampler).

The list of citations showing similar effects of clean room systems,

especially unidirectional flow, on the environmental microbiology of the

operating room, could be expanded (e, g, , see Beck 1964, Beck 1966,

Clark e t al. 1971, French et al. 1973, NASA and Midwest Research Institute

1971, Nelson and Greenwald 1973, Nelson e t al. 1973, Scott 1970, Scott

1971, Tevebaugh and Nelson 1972, Wardle 1973, Wardle et al. 1974,

Whyte and Shaw 1971, Whyte et al. 1973).

B. SOURCES OF AIRBORNE MICROBIAL CONTAMINATION IN CLEAN ROOM OPERATING ENVIRONMENTS

It is widely agreed that the main source of airborne microbes in the

modern operating room is the people within the room and that the level of

microorganisms in the room can be correlated with the type and amount of

their activity (e.g., Bernard e t al. 1967, Cockcroft and Johnstone 1964,

Cole et al, 1965, Ford e t al, 1967). Riemensnider (1966) has shown that the

average individual sheds thousands of viable particles per m i n ~ t e . Smith

and Bruch (1969) have shown that this microbial shedding can be effectively

controlled in clean rooms by the use of certain types of apparel. Microbes

on shed epithelial cells (Bernard e t al. 1965, Davies and Noble 1962) and

fomites from the respiratory t ract (Hart and Schiebel 1939) a r e prime con-

tributorrr to viable particle generation by the surgical team. It has been

obaerved that individuals vary greatly in the number of microbes they shed

(Riemenenider 1967). The problem of the effectiveness of surgical apparel

in controlling such viable particle generation has been well established

(Alford 1573, Belkin 1966, Bergman et al. 1970, Bergman et al. 1972,

Uernard e t al, 1965, Bernard e t al. 1967, Charnley and Eftekhar 1969,

Cockcroft and Johnstone 1964, Devenish and Miles 1939, Dineen 1969, Ford

e t al. 1967, Love11 1945, May 1973).

With the advent of U A F ' ) , terns in su rge ry i t was thought that the

l a rge volumes of a i r d i rec ted er the wound s i te would effectively and

rapidly remove any surgical-personnel-generated contamination. However,

recent etudies indicate UAE' sys tems that empll,y a relat ively high speed and number of a i r changes m a y not be a s efficient a s originally believed

in removing people-generated contamination in the operat ing r o o m ( see IV-C).

Gould e t al. (1973) have pointed out that people obstruct ing the airflow

between the incoming a i r and the wound can lead to turbulence and s u s -

pension of microbial aerosols , with eventual settling of organisms in the

wound. Walter (1970) s t a t e s that ventilating a i r contributes t o the problem

of a i rborne contamination and that l aminar flow concentrates organisms

in the surgica l wound.

Often i t i s felt that the clean room will c u r e a l l the problems of

operating room contamination. Michaelsen e t al. (1 967) caution a s follows:

"The room will never be able to cornpens-te for c a r e l e s s techniques by

w o r k e r s involved. " This point has a l so been emphasized by Shooter and

Will iams ( 1961 ), who note that the c a r e with which asept ic techniques a r e

c a r r i e d out h a s a t remendous impact on seps i s originating in the operating

roQm.

C. CLEAN ROOMS AND IMPROVED SURGICAL APPAREL

In the ini t ial applications of UAF to su rge ry lit t le concern was shown

over the tradi t ional surgica l g a r b which was t r ans fe r red to this rew surgica l

arena. However, with impetus f r o m Sharnley (Charnley 1964), a number

of surgeons began investigating the m e r i t of improved garment sys tems

in UAF. Charnley and Eftekhar (1969) inspected cotton textile gown

mate r i a l and found aper tu res up t7 50 pm i n d iameter . ~ n d speculated that

o rgan i sms could be forced through the f ibe r s of the textile and resu l t in

d i rec t contamination of the wound. They a l so noted that such a route for

wound infection f rom the surgeon's body could escape detection by volumetric

a i r s a m p l e r s and settling plates. Charnley recommended, f r o m th is and

h i s previous work, that a body exhaust sui t (composed of a microbe-

impermeable ma te r i a l and an asp i ra to r for removal of nasophar yngeal

exhaust and body cooling) be employed in operating rooms that ut i l ize

special air-handling davices, i. e . , UAF.

The development by NASA of biological isolation garments (Guyton

e t al. 1967) for the isolation of s t e r i l e spacecraf t a lso se t the s tage for the

incorporation of highly efficient microbia l b a r r i e r s y s t e m s in UAF s u r g e r y

i n the United States. Jones e t al. (1972) have demonstrated the value of face

exhaust masks in conjunction with UAF during mock su rge r i e s . Wardle e t al.

(1 974) have shown the m e r i t of body exhaust su i t s patterned in principle af ter

Charnley's su i t s (but s imi la r in appearance to the NASA bioisolation su i t ) in

the reduction of wound s i te contamination during orthopedic procedures p e r -

formed under UAF conditions. They noted an approximately two-fold

reduction i n a i rborne c o ~ t a m i n a t i o n a t the wound s i te , based on a s e r i e s of

129 orthopedic procedures. Herndon (1973) h a s found the body exhaust con-

cept to be of value in reducing wound si te contamination in an operating room

supplied with HEPA-filtered a i r . Most recently, Poplack e t al. (1974) have

described a self-contained isolation ga rment sys tem that, i n principle, may

have applicability to surgery .

The above work demonst ra tes the value of improved microbia l

b a r r i e r s between the surgica l personnel and the operating room environment

in t e r m s of reduced microbial levels a t the wound site. It does not provide

a measure of value in t e r m s of the control of postoperative wound infection.

however , i f viewed with the philosophy that the incidence of wound infection

(especial ly for clean s u r g e r y ) can be corre la ted with the environmental

microbiology to which the wound i s exposed, i t would appear that such tech-

niques would be of value in infection control. To prove this ctat is t ical ly,

llowever, i s probably impract ica l because of the inherent difficulties i n such

an investigation ( see Section V-A-4): the change in infection r a t e s that might

be expected with such a relat ively smal l improvement i n the environment

would appear to be slight.

An encouraging feature of the application of improved appare l sys tems

in su rge ry i s that they have refocused the attention of the surgica l community

on people a s the leading microbial polluters of the operating room environ-

ment. This problem was well recognized long before the introduction of

clean room surgery . F o r example, Adams (1957) found that, when the re

was no act ivi ty in his opera t ing rooms , the number of colonies forming on

fallout p l a t e s was e s sen t i a l l y z e r o ( a i r sampled f r o m the air-condit ioning

inlet ducts w a s e s sen t i a l l y s t e r i l e ) ; h e found apprec iab le counts when p e r -

sonnel (and pa t i en t s ) w e r e p re sen t . Hence, he w a s convinced that human

act ivi ty i n the opera t ing room is a n impor t an t s o u r c e of a i r b o r n e contami-

nation. His ove ra l l conclusion w a s that m o r e pro tec t ion i s n e c e s s a r y for

su rg i ca l wounds than just the provis ion of s t e r i l e a i r and that s t r i c t clothing

and masking m e a s u r e s m u s t he inst i tuted to cont ro l personnel shedding.

It h a s been shown (e. g . , Cor i e l l 1968) that HEPA-f i l te red a i r

de l ivered through conventional a i r conditioning ducting i s capable of producing

operat ing r o o m envi ronments that exhibit z e r o mic rob ia l counts when people

a r e not present . Laufman (1973) h a s cited such r o o m s as suffer ing f r o m

i n t r a m u r a l contaminat ion only a s a function of inadequate util ization of the

rooms in t e r m s of g a r m e n t s a n d / o r technique. (Laufman (1973) c i t e s his

unpublished work a s indicating that cu l tu re s of a i r immedia te ly o v e r the

open su rg i ca l wound w e r e a lmos t un ive r sa l ly s t e r i l e r e g a r d l e s s of the a i r -

handling s y s t e m and tha t this i s apparent ly due to t he "upward convection

c u r r e n t s f r o m the w a r m wound into the coo le r environment . " ) Recent

s tud ies (Herndon 1973, LeDoux and Gustan 1974) indicate the possibi l i ty that ,

with p r o p e r attention to a sep t i c technique and an emphas i s on cont ro l of p e r -

sonnel and pat ient (Dineen 1969) genera ted mic rob ia l contamination (along

with adequate a i r f i l t ra t ion) , the leve l of m i c r o b e s a t the wound s i t e can be

reduced to a magnitude comparable to that achieved by U A F s y s t e m s .

D. E F F E C T O F CLEAN ROOM AIRFLOW CONFIGURATION ON WOUND SITE CONTAMINATION

In using a c lean room for su rge ry , which type of a irf low r e s u l t s i n

the m o s t effect ive cont ro l of mic rob ia l contaminat ion a t the wound s i t e - turbulent, horizontal , o r ver t ica l? As h a s a l r eady been pointed out, although

turbulent-flow c lean r o o m s provide e s sen t i a l l y s t e r i l e a i r a t the in le t points

( a s pas sed through HEPA f i l t e r s ) , they a r e not a s efficient a s unidirect ional

flow s y s t e m s i n prevent ing l a t e r a l sp read of contaminat ion and in providing

f o r a rapid r emova l of a i rbo rne contaminat ion through a high number of a i r

changes p e r unit t ime (although, a s pointed out in Sect ions I V - B and -C, th i s

aspec t of UAF m a y have sho r t comings i n the s u r g i c a l application).

The re fo re , the quest ion i s f requent ly reduced to which unidirect ional a i r - flow configuration, ve r t i ca l o r hor izonta l , p rovides for the m o s t effect ive

cont ro l of mic rob ia l contaminat ion a t the wound s i t e3

McDade e t al. (1965), in repor t ing on NASA-sponsored ef for t s t o con-

t r o l mic rob ia l contaminat ion of spacec ra f t su r f aces , have indicated tha t

v e r t i c a l flow s y s t e m s appear to be supe r io r . NASA mic rob ia l contaminat ion

cont ro l techniques during a s s e m b l y of fl ight c r a f t have re l ied pr incipal ly on

v e r t i c a l unidirectional flow envi ronments (e. g . , Chr i s t ensen and Ohanesian

1970, E r v i n 1968).

The f i r s t u s e of a unidirect ional flow unit i n the United S ta t e s o c c u r r e d

a t Bataan h4emorial Hospi tal i n Albuqcerque, N. M. ; i t provided v e r t i c a l flow.

However , a s this technology g rew in popular i ty among surgeons , i t was

quickly recognized that ve r t i ca l flow envi ronments w e r e much m o r e expen-

s ive to i n s t a l l than w e r e hcrixontal . Only r ecen t ly have da ta appeared that

e lucidate the effect of unidirect ional a irf low configuration on the leve l of

mic rob ia l contaminat ion a t the su rg i ca l wound si te .

Scott e t al. (1971) compared hor izonta l v e r s u s ve r t i ca l unidirect ional

flow in indus t r i a l c lean r o o m s (s tudies of turbulent flow conventional operat ing

r o o m s w e r e a l so conducted). T h e s e w o r k e r s found tha t the mean number of

b a c t e r i a / f t 3 ( t ) a t c r i t i c a l work s i t e s w a s reduced t o 0 i n the v e r t i c a l flow

indus t r i a l c lean room, and t o 0.2 (0. 007/C) in the hor izonta l flow indus t r i a l

c lean room. T h e i r conclusion ( s e e a l s o Scott 1970) was that the evidence

pointed to ve r t i ca l flow a s the opt imum airf low configuration for application

i n the operat ing room.

Whyte e t al. (1973) studied the effect of a irf low configuration on wound

s i t e contaminat ion during opera t ions on the spine and total p ros the t ic

r ep l acemen t s of the h ip and knee. The unidirect ional flow unit was con-

s t ruc t ed so that, through use of a baffle, the a i r f low could be in te rchanged

between v e r t i c a l and horizontal . T h e s e w o r k e r s found that, a t a i rf low

speeds of 60-80 f t /min (18. 3 to 24.4 m l m i n ) , the bac t e r i a l count would be

reduced by approximate ly 90% with hor izonta l flow and by 97-99" with

vertical flow. At speeds of 60, 80, and 100 ft/min (18.3, 24.4 and

30.5 mlmin), 3.5, 9, and 4.5 t imes less airborne bacteria were found,

respectively, with vertical flow than with horizontal. They note that these

differences were seen when conventional operating room attire was worn;

and add that, with impervious clothing, the difference might have been nil.

Wardle (1973) in a study of two different unidirectional-flow operating

rooms (one vertical, one horizontal), conducted during orthopedic surgery

that was designed to segregate airflow configuration a s the cr i t ical variable,

found that vertical flow provided superior control of airborne microbes a t

the wound site. Although surgeons in both operating rooms wore body-

exhaust suits composed of microbe impermeable material, average wound

site contamination levels of 0.60 colony-forming units/m3 (as detected with

a sli t sampler) and 0.16 (with a membrane sampler) were found in vertical

flow, compared to levels of 3.6 and 3. 9, respectively, in horizontal flow.

Van Der Waaij and Van Der Wal (1973) performed a study of UAF

configuration under nonsurgical conditions. Their conclusion was that cros s-

flow (horizontal flow) is more advantageous as compared to downflow (verti-

cal flow) because contamination upstream from the patient is easier to

prevent. They observed that a t a i r velocities of 0.2 m / s the downflow

environment provided for a more rapid removal of experimental aerosols

(10 s versus 60 s for an aerosol formed from a suspension of 1 0 5 g .

coli/m P), but that the removal was mainly by sedimentation - an undesirable - feature for operating conditions. Removal in crossflow appeared to be by

the airstream. These workers hypothesized that smaller aerosols, a s

experienced in real life surgery, would mitigate the differences they found

between the two airflow configurations.

Clean room technology cannot be relied upon to compensate totally for

inefficient apparel system8 o r improperly executed aseptic technique.

Human beings a r e the prime sources of microbiological contamination

in the operating room. Given an operating room of proper design and main-

tenance, HEPA-filtered a i r introduced into that room will remain essentially

free of the predominant causative agents of wound infection until

contaminated by human sources. Although the configuration of clean room

airflow may have an effect on wound site contamination, i t would appear

possible to negate it by use of absolute microbial barr ier techniques that

separate the surgical team and patient from the operating room

environment.

SECTION V

CLEAN ROOMS AND SURGICAL WOUND INFECTION

It has been es t imated that 7. 5% of surgica l wounds become infected

(National Academy of Sciences - National Resea rch Council 1964). In mos t

cases , the organisms causing postoperative wound infections a r e staphylo-

cocci; however, infections caused by Escher ichia , Proteus , Pseudomonas

and o ther gram-negative genera a r e becoming increasingly frequent

(E'eingold 1970, Fekety and Murphy 1972, Johnson 197 1 ).

Surgical clean rooms a r e used in hopes of reducing the incidence of

surgica l wound infections - m o r e prec ise ly surgica l ly induced wound infec-

tions. Surgically induced wound infections a r e usually defined a s infections

that originate in the operat ing room and a r e due to contaminating events

that deposit exogenous infection producing organisms in the surgica l wound.

The control of exogenous organisms by ster i l izat ion, aseptic technique,

and air-handling sys tems has been tradit ionally considered in operat ing

room protocol. Endogenous organisms, however, a r e not general ly

regarded a s being amenable to control by air-handling sys tems. Inherent

in the application of clean room technology to s u r g e r y i s the rat ionale that

s o m e wound infections a r e caused by microbes that gain en t ry to the wound

via operating room a i r and, therefore , a reduction in the level of a i rborne

microbes a t the wound s i t e can lower infection ra tes . The controversy

surrounding th is view will be discussed.

The concern over the m e r i t of clean room technology fo r surgica l

application has of necess i ty identified a number of related problems

regarding operating room a i r quality, and these will be investigated in

this section.

A. SURGICAL WOUND INFECTIONS

1. Definition

The t e r m "eurgical infection" can be used in a sense that encom-

p a s s e s m o r e than the surgica l wound proper. F o r example, the inser t ion

of a catheter into the ur inary tract, a common surgery-related procedure,

accounts for the most prevalent hospital-related (or nosocomial) infection.

Laufman ( 1973) cites other types of surgery-related infections a s follows:

respiratory infections, cellulitis, abscesses, infected body cavities (e. g. , peritonitis and pleuritis), infected organs remote f rom the surgical site,

septic thrombi, mycotic emboli, toxemias, and septicemias.

The present discussion i s directed to one specific type of surgical

infection-surgical wound infection. Beck and Carlson (1962) have pre-

sented the following parameters a s requiring consideration in the formula-

tion of a workable definition of a surgical wound infection: ( I ) the wound

or ig i i~ (planned vs. traumatic); ( 2 ) the c lass of the surgery ( see below);

(3) the state of the patient (old, young, debilitated); ( 4 ) the type of operation;

( 5 ) the cri t ical postoperative period for appearance of an infection; (6 ) the

site of suppuration; ( 7 ) the microbiology of the infection; and (8) the degree

of infection. They state that only with a precise identification of the

cr i ter ia employed in the definition of a surgical wound infection can a mean-

ingful statistical statement be made in the comparison of infection data.

Considering the above, Beck and Carlson arrived at the following basic

definition of a surgical wound infection: "An inflammatory reaction of a

wound, beyond the inflammatory reaction of healing, with the accumulation

of pus. "

An important step toward refining the discussion of surgical wound

infections came in 1964 when a nationwide study, coordinated by the National

Academy of Sciences (National Academy of Sciences - National Research

Council 1964), classified surgical operations a s a function of their cleanliness

level. Four c lasses were identified a s follows:

1) Clean.

Gastrointestinal o~ respira tory t rac t not entered; entrance of

genitourinary o r bil iary t r ac t s in absence of infected urine o r

bile; no inflammation; no break in technique.

Subdivision: Refined-clean (elective, not drained, and primarily

closed).

Clean-contaminated.

Gastrointestinal o r respira tory t rac t s entered without significant

spillage; bil iary o r genitourinary t rac t s entered in presence of

infected bile o r urine; minor break in technique.

Contaminated.

Major break in technique; acute bacterial inflammation without

pus; gastrointestinal spillage; recent trauma from relatively

clean source.

Dirty.

Pus encountered, perforated viscus, old traumatic wound o r

d i r ty source.

The study found the incidence of surgical wound infection to vary markedly

a s a function of operation c lass with Clean procedures yielding 7. 5% infec-

tion (Refined-clean. 3. 8'70) ; Clean- contaminated, 10. 5%; Contaminated,

14. 370; and Dirty, 26. 3%.

The controversy among physicians a s to the definition of a surgical

wound infection remains when attempts a r e made to define "surgically

induced infectione" - those identified a s being directly influenced by

clean room technology (see Section V-D). Quite often what one surgeon

would classify a s a surgically induced infection would be cited by another

a s one with a different etiology, e. g. , caused postoperatively in a di r ty

ward. The predominant thinking among orthopedic surgeone is that

only deep infections should be considered as possibly surgically induced

(NASA 1971).

A number of wounds - some superficial and some deep - have been

found to drain s ter i le pur. Such conditions r a i s e the question a s to the

involvement of microbes in these cases. Was the "infection" a resul t of

physical conditionlr a t the surgical locus (e. g., tight stitches o r prensure

from an ill-fitting prosthetic device), o r of microber that had completed

their growth curve, o r of microber that were not detectable by the culture

methods employed? Such cases a r e included in some infection stat ist ics

but not in others.

The type of operation should obviously be a par t of any definition of

surgical wound infection. This i s of particular consequence in the discus-

sion of the role clean rooms play in controlling infection rates, While an

intestinal operation which focuses on a microbe-laden environment would not

appear likely to benefit from clean ai r , a total hip replacement might,

Shaw e t al. (1973) have cited data that shows that the rate of wound infection

for different types of operations, done in the same operating room, can vary

from 0.8 to 50%; hence the need for discussing wound infecticn in t e rms of a

particular type of surgical procedure.

2. Factors Involved

.-i number of factors can be cited which have a bearing on the

incidence of postoperative wound infection (and possibly the definition of such)

(Cohen e t al. 1964, Davidson e t al. 1971, National Academy of Sciences - National Research Council 1964). The following a re most often discussed in

this respect: Microbial contamination of the wound during surgery; patient

age, sex, race, and condition (e.g., diabetes, steroid therapy, obesity, and

malnutrition a r e considered relevant); presence of a remote infection: type of

wound closure; wound drainage; duration of operation; use of prophylactic

antibiotics; urgency of operation (e. g., emergency versus elect!ve surgery);

and duration of preoperative hospitalization. The interplay of these factors

can often confound attempts to t race the origin and compare the frequency of

surgical wound infections.

3. Sources

Where do infectious organisms a r i se in the operating room?

Four reservoirs of operating room microbes exist: the surgical personnel,

the patient, the surfaces of inanimate objects within the room (the walls,

floors, instruments, etc. ), and the a i r entering the room (from an a i r -

handling system p e r - se or from the opening and closing of operating room

doors. ) From the standpoint of airborne contamination (see Section I V - R ) ,

the hnman sources a r e very significant and exist primarily on fomiter in

the form of nasopharyngeal droplets and shed epithelial scales (Bernard et al.

1965, Davies and Noble 1962, Hart and Schiebel 1939). The role of intimate

objects in airborne contamination as i t affects wound s i te contamination

appears minimal. In the modern operating room, the incoming a i r will prob-

ably exhibit a minirnum of microbial contamination i f the filtration system i s

in good working order ( see Section IV-C).

This raises the question: Why employ a clean room if the conventional

air conditioning of an operating room can provide a i r low in microbial con-

tent? The answer moat commonly given i s that the clean room provider a i r

filtered to a higher level of efficiency and discrimination; but more impor-

tantly that, in the case of UAF at least, it provides a high volume flow of a i r

over the wound site and adjacent critical locales and therefore flushes away

any microbes that might otherwise contaminate the wound (see Sections I V - B

and -D).

4. Statistics

It would appear that the ultimate test of the theory of clean room

infection control would involve a double-blind study with the only variable

being the air-handling system. Unfortunately, such a study has not been

done, and possibly never will be. If some medical group(e) we-e to venture on

this experiment, i t would require that they control such potential variables

a s the surgical personnel involved, the surgical technique, and the operating

room protocol throughout the study. In addition i t would necessitate that a

sufficient number of procedures be performed under each experimental condi-

tion to demonstrate that any differences in infection rate ca r ry significance a t

a high level of confidence, This las t criterion i s perhi;ps the most difficult

to meet and still comply with the other experimental cri teria. Lidwell ( l Q . 3 )

notes that a 50% reduction in infection rate from 3.Olb to 1.5% would require

780 observations in each group to demonstrate a significant difference

(P = 0.05) due to the treatment imposed (in the present case, a clean room).

Charnley (1973) states that to establish a clean room a s effective in reducing

infection from 1 to 0. 570 would require 2600 observations and 2600 controls.

Such a controlled study would also have to be responsive to any unique infec-

tion considerations of the type(s) of operation under investigation. F a r

example, i t has been noted that conclusive statements on postoperative wound

infections for total hip replacements require a 2- to 3-yr follow-up after ~ n e

rurgery (Charnley 1972).

Despite the absence of relevant data taken under contro!lec'

experimental conditions, there have been a number of a t tempts to compare

infection rat,.-s between clean room and conventional operating environments.

; .aufman (1973) c i t e s data from four different surgica l t eams pcrfornring

total hip replacements in conventional operating rooms that indicates an

overa l l infection ra t e of 0.45% for 3b22 procedures with a 9- to 42-mo

patient follow-up and notes i t s cotrrparability to the best reported by

Charnley using his special air-handling systei:~, Such a ra te i s , according

to Charnley, of an o r d e r of magnitude esp ress ing the l imi ts of control of

exogenously induccrr infection d u r i n ~ su rge ry (Charnley 1973). (Charnley

(1973) bel ieves that the res idual 0. 5% infection ra t e he current ly exper iences

with h is rcplacements i s due to infections of endogenous origin. ) Whitcontb

( i 9 7 l ) r epor t s an infection ra t e of 0.7% for 3408 operations performed in

ver t ica l unidirec tional flow and contras ts this with r a t e s of 0.93% and 1. 14%

for 4162 and 4091 operat ions, respectively, performed in two conventional

operating rooms. Whitconrb and Clapper ( l9hb) feel that the already low

infection r a t e experienced lessened the magnitude of infection r a t e reduction.

How authoritative a r e such compar isons of infection r a t e s a s de te rmi -

nants of the m e r i t of c lean r o o m s ? Careful inspection of the groups that

a r e compared often revea l s o ther var iables bes ides a i r quality that could

influence infectior, r a t e s , e. g. , the u s e of prophylactic antibiotics, the type

and tcchnique of surgery , the operating room protocol, and even the patients

themselves. Therefore , it is obvious that such compar isons do not ecienti-

fically answer the quest ions of the re la t ive m e r i t of clean rooms in surgery.

B. AIRBORNE INFECTION OF SURGICAL WOljNCS

Chapin (1914), short ly af ter the turn of the century, c i tes a changing

attitude in the medical community concerning p.:rbo..ne infection in aseptic

surgery . He notes that the rationale for the e: l~p?-taais , in "modern su rgc rv , "

on a i rborne infection had i t s origin in the work!: of Schwann, Pas tcur ,

Tyndrl l , and o thers on spontaneous generation, putrefaction, 2nd fcrt11er.t;-

tion. Tlrese works showed that, when microorganisms floating in the a i r

w e r e excluded, these p r o c e s s e s did not occur. 'ience, the initial assumption

i n su rge ry that a i r was the principal source of infection appears quite natural.

Chapin p r e s e n t s the philosophy that both the number and v i ru lencr of

m i c r o b e s m u s t be cons idered i n de te rmining infection and the iAea "that a

s ingle g e r m will cause d i s e a s e i s a myth of the e a r l y days of bacteriology. '

It i s s e e n today that s o m e su rgeons do not c c n s i d e r the one -mic robe theo ry

a myth, and hence a r e swayed by the mic rob ia l control afforded by clean

rooms. On the o the r hand, o the r s have found that, f o r p a r t i c u l a r s u r g i c a '

s i tuat ions, s u c c e s s i s independent of the environmental n~ ic rob io logy of the

operat ing room.

It i s u n d ~ u b t e d l y t r c e that number and v i ru lence of m i c r o b e s a r e c r i t i ca l

p a r a m e t e r s i n infection. Rut how many \*irulent o r g a n i s m s a r e n e c e s s a r y to

cause an infection and does the p re sence of m i c r o b e s mean a n inevi table

infection? Again the o ther f ac to r s - the patient, the type of s u r g e r y , etc. - m u s t have some bearing on the answer . Owing to the complexi ty of the

p r o c e s s involved in answer ing this quest ion, v e r y few conc re t e a n s w e r s a r e

available. Burke (1963) found that 100°'b of thorac ic and abdomen wounds

exhibited microbia l contamination a t the end of su rge ry . Coagulase-posi t ive

staphylococci w e r e p r e s e n t i n 92"; ( ave rage of 14 CFU::: p e r wound); however

only 4% of the wounds became infected. Davidson e t al. (1971b), i n eva lu-

ating 1000 s u r g e r i e s , found that the p r e s e n c e of bac t e r i a i n the wound a t the

end of s u r g e r y was th ree t i m e s a s significant a s any other f ac to r i n the inc i -

dence of wound infection. Condie and F e r g u s o n (1961) noted that wound c lo-

s u r e technique in dogs h a s a highly significant effect on the development of

infection in wounds contaminated with l a r g e numbers of v i ru len t s taphylococcie

Nelson e t a l . (1973) observed a 221'0 contaminat ion i n wound cu l tu re s taken in

a conventional operat ing room a s con t r a s t ed to 5:; o r l e s s i n a UAF operat ing

room; a cor responding d rop in infection r a t e was evident i n compar ing the

two envi ronments ( s e e Section V-D-1).

The l i t e r a tu re on a i rbo rne infect ion commonly makes r e f e rence to the

following mechan i sms of spreading a i r b o r n e contamination: contact, d r o p -

l e t s , droplet nuclei, and dust. Langmuir (1961) o f f e r s definitions of t hese

t e r m s ; the following d e s c r i b e s them i n t e r m s of operat ing room cons ide ra -

tions:

1 j Contact.

Ordinar i ly , contact s p r e a d r e f e r s main ly to contiguous t o l ~ c h -

:::CFU = colony-forming units.

ing; however, this mechanism can be classified a s a form of

airborne spread when the contamination of objects (e. g . , surgical I + i

instruments) originates primarily from "dirty" operating room

air. [

2) Droplets.

Microbes expelled from the mouth, and sometimes from the

nose, during talking, coughing, and sneezing. Since such drop-

lets settle rapidly, they do not spread beyond the immediate

vicinity of the point of origin (usually less than 1 m).

3) Droplet Nuclei.

Residues originating from small dried droplets that remain

suspended. These contaminants may be spread throughout the

operating room on a i r currents o r passed through ventilating

ducts.

4) Dust,

Unusually large particulates that exist on floors, clothing, etc. ,

and may be periodically s.sspended and resuspended in a i r by

human activity.

Langmuir points out that methods for the control of contact (defined in the

s t r ic t sense) and droplet mechanisms of spread, unlike droplet nuclei and

dust, a r e not amenable to the engineering approaches of controlled ventila-

tion. ultraviolet irradiation, disinfectant vapors, and dust suppression.

A fifth mechanism of airborne spread in surgery i s the shedding of

epithelial fomites that car ry microorganisms to the wound site. The use of

surgical gowns and drapes i s directed towards the control of such contamina-

tion. The shortcomings of the ordinary approach to such control and the

possible benefits of clean rooms a re discussed in Section IV-C,

For infection to be spread by the airborne route, the organism

involved must be able (in many instances) to survive severe desiccation.

Staphylococci, streptococci, tubercle bacilli, some viruses, and bacterial

spores are capable of airborne transmission, whereas a number of gram-

negative organisms a r e not (Dimmick and Akers 1969).

Noble e t al. (1963) repor t that airborne organisms associated with

human disease o r ca r r i age a r e usually found on par t ic les in the range of

4-20 pm equivalent diameter. * The range of part icle s ize distribution was

found to be determined by two opposing factors: gravity, which tends to

eliminate the large par t ic les ; and the fact that the l a rge r the par t ic le the

m o r e likely i t i s to c a r r y a microorganism. They found that the median

equivalent d iameters measured for microbe-associated par t ic les were much

grea te r than the dimensions of the microbial cel l , thus indicating that a i r -

borne organisms a r e usually disseminated into the a i r in association with

mat te r derived ei ther f rom the menstruum with which they were originally

associated o r f rom some transient rest ing place. Greene e t al. (1962) studied the relationship between a i rborne microbial contamination and

part icle size i n the hospital environment and found that, in 75.67'0 of the

samples, the majori ty of the contaminants were associated with a i rborne par -

t ic les >5 pm. May and Pomeroy (1973) in a study of bacteria! dispersion f rom

the human body found in excess of 92% of colony-forming part icles to be

associated with par t ic les 2 5 p .

As has been noted previously (Section IV-A-Z), there is ample evi-

dence a s to the efficacy of clean rooms in reducing the number of a i rborne

microorganisms in the operating room. It is all well and good if these sy s -

t ems reduce airborne contamination, but such contamination control is of

little value if there i s not a concomittant reduction in the incidence of post- ! operative wound infection.

There is much to be found in the l i tera ture concerning airborne

infection in surgery a rd a representat ive fract ion of i t will be explored here .

Before entering into such a discussion, the reader must be cautioned on the

complexities inherent in any such discussion. The cr i t ica l question i s "Do

clean rooms s e rve to reduce a i rborne infection of surgical wounds?" Before

that question can be answered, it will be necessary to determine if airborne

infection in su rgery does in fact occur. The evidence, pro and con, will

involve variables which in themselves could be a s important a s the one

under discussion - the level of microbes in operating room a i r . Such factors

aside, an attempt will be ma ie to resolve the crux of the mat te r , i, e. , can

*"The equivalent part icle d iameter of a sphere of unit density which has a settling ra te in air equal t o that of the part icle in question" (Noble et al. 1963).

the microbial quality of the operating room a i r be shown to be related to

wound infection r a t e s ? An aff irmative answer to this question would appear

to argue in favor of clean rooms; a negative, against. However, it must be

r emembered that the geneyal case may not always be applicable to the special.

What follows is an at tempt to p resen t pertinent data, mostly p r o o r

con, on the value of reduced levels of a i rborne microbia l contamination in

lowering surgica l wound infection ra t e s . It should be noted that perhaps a

bias exists in such a presentat ion s ince positive r epor t s on the effect of

e f fo r t s t o lower the microbia l content of operating room a i r may be m o r e

likely to be reported than negative.

1. P r o

Blowers e t al. (1955), proceeding on the p r e m i s e that a i rborne

infection is the p r i m e agent in surgica l wound infection, d i rec ted their

attention to reducing the numbers of a i rborne microbes in the hospital in

genera l and the operating room in par t icular . The i r work deal t with ches t

su rge ry and was prompted by the appearance of penici l l in-resistant

Staphylococcus au reus infections. Circumstances surrounding s u r g e r y led

them to believe that the principal mode of t r ansmiss ion fo r these infections

was airborne. Correc t ion of faulty operating room protocol and ventila-

tion improved the air quality and was cor re la t ed with a reduction in infection

r a t e f rom 10.9 to 3.9% (Table 2).

Shooter e t al. (1956) found that by creat ing a positive p r e s s u r e in the i r

operating room relat ive t o the co r r idor and instituting a powerful s t r e a m of

filtered a i r a c r o s s the wound s i t e they were able to reduce a i rborne contami-

nation and simultaneously drop the wound infection r a t e f rom 9 to 1%

(Table 2).

Burke (1963) determined, using a staphylococcal phage typing method,

that the a i r in contact with the surgica l wound was responsible for contami-

nat ion of 6870 of the wounds, followed closely by pat ient-carr ied s t r a ins from

the nose, throat , and skin which contaminated 50% of the wounds. This study

was aimed only a t identifying the sources of coagulase-positive staphy-

lococcal s t r a ins found in the wound just before c losure , and, because of the

problem of s t r a i n shift, conclusive s ta tements could not be made a s to the

sources of the organisms yielding infections. Abdominal and thoracic pro-

Table 2. The effect of reduced airborne microbial levels during surgery on wound infection rate

Airborne microbial levels

Method of C F U ' / ~ ~ ~ Infection, 70 ~ ~ U / f t Z l r n i n

reduction Reference

(per l i t e r ) (per m21min)

Before After Before After Before After

Improved ventilation and protocol

Improved ventilation

Ultraviolet

Improved protocol

Ultraviolet

( f )

Improved ventilation

Improved ventilation

Blowers e t al. (1955'

Shooter e t al. (1956)

National Academy of Sciences (1964)

Har t e t al. (19b8l

Seropian and Reynold (1969)

Charnley (1972)

Gould et al. (1973)

a~olony-forn i inR units.

'petri dish agar surface a r e a of 0.085 ftL (0.0079 m L ) assumed.

' ~ a t e s for refined-clean procedures ( s e e text for discussion of ra tes for these and other procedures) .

d~nfec t ion deaths of nonhuman subjects.

e ~ i t e d by Hart e t at. f19f~8) a s t y p ~ c a l example of UV effect on airborne bacteria in the operating room.

' ~ i r b o r n e rontamlnation and infection ra tes a r c shown in romparlson of operating room environments in two hospitals.

' ~ v e r a ~ e sedimentation plate counts - not expressed on a unit a rea , t ime basis .

h ~ e e p infections in total hip arthoplasties.

'Infection ra te for a l l operations before and after introduction of UAF. --

cedures were monitored. No wound was found to be steri le upon closure;

92% contained coagulase -positive staphylococci in numbers sufficient t o make

them easily identifiable (the average number was 14 CFU; total staphylo-

cocci were 24.2 CFU).

Cockcroft and Johnstone (1964), in a study of infections following open

heart surgery, attributed contamination of the wound site to a i r currents

which disseminated personnel-generated microbes.

Walter et al. (1963) have attributed an airborne origin of wound infec-

tion to a disseminating nasopharyngeal staphylococcal c a r r i e r present in the

operating room during an elect ive nephrectomy and cholecystectomy on two

healthy patients (ages 24 and 44). S ter i le a i r was introduced into the room

a t positive p r e s s u r e with scven changes of a i r p e r hour. The exogenous

staphylococcal infections occurred despite the tremendous dilution of the

contamination from the c a r r i e r (who was located in the per iphery of the

room), which resulted i n only 11.270 of the a i r samples containing the p a r -

t icular s train. The culpable s t r a in was a lso detected on the ins t rument

table and m a s k s of the surgica l team. The mechanism of a i rborne contami

k nation spread was cited a s droplet nuclei. j i Payne (1767) a lso points to the origin of infection-producing o rgan i sms

shed f rom a member of the surgica l team and diluted i n a i r p r i o r to wound

impingement, hence exposing the wound to a relat ively low number of

challenge organisms.

Vesley e t al. (1966) performed an interest ing s e r i e s of exper iments to

define the effect of environmental microbiologic control on surgica l infection

ra tes . The "patients" studied were dogs ra the r than humans, because of the

impossibility of manipulating environmental p a r a m e t e r s in the p resence of

susceptible patients. Laparotomies and thoracotomies were performed.

The microbiologically clean t e s t operating room exhibited a i r contamination

over threefold l e s s than the control room. Although the major i ty of infection

deaths appeared to be of endogenous origin (62?;b), the overa l l reduction i n

fatal infection r a t e was from 56% i n the "controlt ' room to 287'0 i n the "s ter i le"

room. Hence, the "control" room, with a three and one-half fold g r e a t e r a i r

contamination level, had twice the infection death ra t e (Table 2 ) .

I n an e f fo r t to reduce the infection r a t e found with h i s total hip a r t h r o -

plasty procedures, C h ~ r n l e y (1964a, 1964b) instituted means to control

exogenous contamination of wounds. The resu l t s (Charnley 197.., Charnley

and Eftekhar 1969) point to a drop i n infection r a t e f rom 7% to 1. 570, ppri-

mar i ly attributed to the instal lat ion of an air-handling sys tem that provided

essential ly s t e r i l e a i r to the operat ive field (Table 2) .

Alpert e t al. (1971), using a surgica l i so la tor that provided for i so la -

tion of the wound from the ambient operating room environment, found a

reduction in wound infection f rom 7. 870 i n a conventional operating room to

2. 37'0 with the isolator sys tem in use ,

Gould e t al. (1973), studying a s e r i e s of 190 total hip ar throplas t iea

(80 operated i n UAF; 110 without), were able to co r re la t e a reduction i n deep

wound infections attributable to improved a i r quality (Table 2).

The biocidal action of ultraviolet (UV) radiation i s well established

(Hollaender 1955) and has been intensively studied a s to i t s ability to reduce

microbiologic contamination of operating room a i r and, a s a consequence,

postoperative wound infection ra t e s . Har t e t al. (1968) in reviewing the i r

30 y e a r s of experience with UV i n the operating room c i t e s an unequivocal

benefit of UV i r radia t ion in reducirg infections of clean, genera l surgical ,

cardiac , thoracic, orthopedic, a ~ d neurosurgical wounds due t o i t s de le ter i -

ous effect on a i rborne microbes [ 'Table 2). F r o m 4293 operat ions performed

without UV irradiat ion, an i n f e c t i ~ ~ n ra te of 3. 2% was observed a s compared

to 11, 840 operat ions with UV irradiat ion and an infection r a t e of 1. 5'7'0. The

following reductions in infection r a t e s w e r e noted f o r Sifferent c l a s s e s ( see

V-A-1) of operat ions performed with UV when compared :o the controls:

C lass of operat ion

Refined clean

Other clean

Contaminated (included clean contaminated, contaminated, and d i r ty )

With UV

Number of operat ions

P e r c e n t infected

Without UV

Number of operat ions

P e r c e n t infected

Overholt and Betts (1940) showed that UV i r radia t ion reduced infection

r a t e s in clean thoracoplastic procedures f rom 13,870 to 2, 7'%, and Woodhall

e t al. (1949) reported infections i n clean neurosurgical operat ions were

reduced f rom 1.170 to 0.470 a s a r e su l t of U V i r radia t ion of the in t ramura l

a i r .

P e r h a p s the mos t extensive study of a i rborne infection in s u r g e r y was

that coordinated by the National Academy of Sciences - National Resea rch

Council (1964) to de termine the influence of UV i r radia t ion in the operating

room on the incidence of postoperati\.e wound infection, The study

5 6

encompassed 5 institutions and 16 operating rooms. U V irradiation provided

significant reductions in airborne bacteria in the operating rooms (Table 2),

but the overall infection ra te in the irradiated rooms (7.4%) was comparable

to that found in the control rooms (7.5%). However, when the comparison

was confined to refined-clean wounds (see Section V -A-1 for wound classifi-

cations), the c lass least susceptible to contamination from sources other

than a i r (i. e. , endogenous), a drop i n infection ra te from 3.8% for the con-

t rol wounds to 2.9% for the irradiated was observed (P = 0.05). The study

of refined-clean wounds represented a large proportion of the operative

wounds observed (6656 out of a total of 15,613). "Other clean" wourids

(5034) also had a lower ra te of infection when irradiated (7.3 versuR 7.57'0),

but the difference was not statistically significant. When other c lasses of

operation (clean-contaminated, contaminated, and dirty) were compared, no

beneficial effect of UV irradiation was noted. In fact, for these c lasses the

ra te of infection was consistently higher (but not statistically significant)

with UV irradiation than without.

2. Con

Bernard and Cole (1962a) in a study of the relationship between

a i r contan-ination and surgical wound infection found inguinal herniorrhaphies

to exhibit an infection rate of 0. 95% (1916 operations) and gastrectomies,

10.2% (825 operations) in s imilar environments. They concluded that wound

infection attributable to a i r contamination was an unimportant factor in the

overall problem of postoperative sepsis. They observed (Bernard and Cole

1962b), however, that the rate of infection of clean wounds (e. g., inguinal

herniorrhaphy) should correla te with exogenous sources of contamination

(ineffective sterilization techniques, excessive a i r contamination, and/or a

breakdown in aseptic surgical technique resulting in a transfer of microbial

contamination from the environment to the patient); it was also noted that

potentially contaminated and dirty wounds risk infection from hoth exogenous

and endogenous sources. They found i t is unrealistic to expect the improve-

rr : nt in a i r quality (unless exceedingly dirty conditions a r e present) to have

any significant effect on contaminated operations (e. g, , gastrectomies). By

attention to housekeeping, traffic control, and isolation techniques, but with-

out using germicidal lights o r air-filtering equipment, these workers were

also able to effect a reduction in airborne contamination from 20 colony- 3 forming unitslft (0.71 /I) to 5 (0. 1811) o r less.

Howe and Marston (l962), i n a study of 330 surgical patients, found

little evidence of airborne transmission, although they attributed the origin

of most of their serious infections to surgical personnel o r patient -source

wound seeding in the operating room during surgery.

Oldstine (1 966) found that airborne t ransmiss ion of staphylococci

p e r s e was of minimal importance in the dissemination of staphylococcal

infection of thoracic operations. Ile states that studies which show a

reduction in staphylococcal infections when th? airborne staphylococcal

count i s lowered a r e biased because the reduction in the airborne count is

accompanied by intensified efforts on the part of hospital personnel to

improve aseptic technique and cleanliness, matters which a r e in themselves

of tremendous infection-control importance.

Seropian and Reynolds (1969) found, in comparing operating rooms

differing up to 8 times in airborne contamination risk, that the lower infec-

tion ra te (1.8 versus 3.6%) prevailed when surgery was performed in the

dir t ier environment (Table 2). The study included a variety of surger ies

and found that the trend held for clean procedures in particular. Airborne

contamination was found not to be a determining factor in the incidence of

wound infection.

Davidson e t al. (1971a), studying 1000 general surgical procedures,

found pathogenic staphylococci to be seldom cultured from a wound at the

end of an operation (positive culturcs usually were precursors of infection

with the same phage type of organiem). Those infections observed to result

from activities in the operating room were judged a s being of an endogenoue

origin; hands and masks of the surgical team could not be demonstrated a s

sources of contamination during the operations,

Phaw et at. (1973) surveyed the incidence of wound infection for a

variety of general surgical procedures and deduced that operation type was

more significant than exogenous factors in the incidence of postoperative

infection. Operations were performed in positive-prereure plenum ventila-

tion operating rooms. The a i r was filtered to a particle size of 5 )rm and

underwent 20 changer per hour: the mean bacterial count war I. 7 l f t

(0 ,06 /1 ) , It war felt that a cornpariron of operationr of r imilar magnitude

m d duration rhould yield rimilar ra te r of infection if the rourcer were

primarily exogenous. Lumbar sympathectomy and hear t and great versels

procedures yielded 1% infection ra te r as compared to 16% for stomach and

duodenum operations and 26% for vascular surgery of the upper thigh. From

these rerul t r i t was concluded that future infection control efforts by the

general surgeon should be directed to the control of endogenous infection and

that laminar flow ventilation rooms o r operating enclosures with a high ra te

of a i r exchange a r e unlikely to produce a significant reduction in general

surgical procedures.

Laufman (1973) s ta tes that evidence is accumulating that shows a

reduction of the wound-site bacterial count to almost zero has shown no

significant effect on an already low infection rate.

Gould e t al. (1973) present data that indicate the introduction of UAF

into the operating room lowered the microbial contamination level at the

wound site, but that for other than total hip arthoplasty deep infections no

significant reduction in infection ra tes occurred (Table 2).

ENDOGENOUS INFECTION

There is increasing evidence that endogenous infections a r e more

prevalent than exogenous ones (Altemeier e t al. 1968, Fekety and Murphy

1972). Altemeier e t al. (1968) l is t five sourcee of endogenous infection a s

follows: skin, respira tory tract , gastrointestinal tract , genitourinary tract ,

regional lymphatics, and blood stream. Unlike exogenous infec tionr, endo-

genous infections a r e not commonly thought to be spread by airborne routes;

however, i t is conceivable that a patient source of organisme could contami-

nate the operating room a i r and reach the wound by a direct airborne

transfer (Gould e t al. 1973) o r an indirect one, for example, via deporition

on inrtrumente pr ior to use. If a clean room were to function in a manner

that would allow effective purging of the rurgical field and hence a removal

of ruch endogenoue rource contamination, i t could porr ibly have an impact

on endogenour source infections.

D. INFLUENCE OF CLEAN ROOMS ON SURGICALLY INDUCED WOUND INFECTION

Up to this point the parameters necer ra ry to a dircurrion of rurgical

wound infection and in particular its relation to airborne contamination in

the operating room have been considered. As ham been mentioned, the crux

of the mat ter of clean roomr in surgery i s the effect of much roomr on

surgically induced wound infections, i. e . , those seeded during surgery and

of an exogenous origin (however, s ee Section V -C, above).

In the whole controversy over the influence of clean rooms on infection

rates, perhaps the most difficult question to answer definitively is whether

or not a postoperative infection was induced at the time of surgery. This

difficulty a r i s e s from an inability to determine accurately the exact point

during patient care at which an infection producing organirm was introduced

into the wound, and its source. Some workers favor the view that surgical

infections a r e introduced primarily in the operating room (Howe and

Marston 1962); others favor the wards (Lindbom 1964, O'Riordan e t al.

1972); and st i l l others cite both locales a s sources of infection-producing

organisms (Cohen e t al. 1904, Williams e t al, 1966). In those instances

where workable phage typing techniques a r e available (e. g., staphylococci),

the irolation of an exogenous s t ra in f rom an infected wound does not prove

conclusively that the responsible contaminating event occurred during

surgery. F o r example, contact between surgeon and patient that extends

into postoperative recovery could conceivably account for the appearance

of infection attributable to a s t ra in of organirm indigenous to the surgeon

(Mitchell e t al, 1959, 0' Riordrn et al. 1972, Williams e t al. 1966).

The emergence of nontraditional pathogenr a r being of clinic&' rignificance

in wound infectionr har found the epidemiologist lacking the phage typing

toolr he had at hir disposal for tracing rtaphylococcal infectionr. The

increasing appearance of a wide variety of organism6 in clean wound infec-

tions ha r placed a determination of their origin beyond the technology

presently available,

1, Orthopedics and Clean Roomr

The orthopedic rurgcon ha8 been the foremort member of the

surgical community in the application of clean room technology for the

control of surgical ly induced infections. In part icular , t he re has been ex-

tenaive use of clean air (especial ly unidirectional flow) in total hip surgery .

Ao performed in conventional operating rooms, these s u r g e r i e s have bee!l

repor ted a s having infection r a t e s of f rom 4 to 12% (Nelson e t al. 1973). In

cont ras t , Coventry (personal communication cited in Nelson e t al. 1973) ob-

s e r v e s a 1% r a t e fo r total hip replacements in a conventional operating room

( s e e a l ao p. 49). The data accruing f r o m these procedures of fers us the

c l ea res t a s s e s s m e n t of infections deemed to be of a surgical ly induced nature.

Orthopedists a r e mos t concerned about deep infections in total hip replace-

ments ( those involving the prosthet ic implant), and i t is often argued that

such deep infections a r e p r ime candidates for su rg ica l inducement and t h e r e -

fore influenceable by clean room technology.

Charnley (1972), in report ing on 5800 total hip replacements p e r -

formed over a 10-yr period, c i tes data to indicate that m e a s u r e s taken to

prevent exogenous infection (improved ventilation and the institution of body

exhaust appare l ) reduced the deep infection r a t e from 7 to 0.5%. Nelson

e t al. (1973), in a smal l s e r i e s of total hip operations, found a deep infection

r a t e of 5.2% in a conventional room (1 33 p rocedures ) and 1.1% (270 proce-

d u r e s ) i n a horizontal unidirectional flow room, IIe notes, howet-er, that

final confirmation of the data will requi re additional follow-up of the

appearance uf postoperative infection. A number of other orthopedic s u r - geons have reported ve ry low infection r a t e s i n U A F (Amstutz 1973, Anspach

and Bakels 1973, Bechtol, 1971, Crane 1972, Faber 1972, Gould e t al. 1973,

Nelson and Greenwald 1973, Rit ter e t al. 1973), but have not performed an

adequate number of control operat ions in conventional rooms; consequently,

these surgeons cannot make a definitive s ta tement concerning the efficacy

of UAF in reducing infection ra tes ,

2. American College of Surgeons Statement

The place of specia l a i r s y s t e m s in r u r g e r y has been voiced in the

fo rm of a s ta tement from, the Operating Room Environment Comtnittee of

the American College of Surgeons (1971 1, The committee took the stand

that "there i n no conclueive evidence a t this t ime that laminar ( laminar

flow in surgica l operating rooms is defined a s a i r flow which is predom-

inantly unidirectional when not obstructed), clean (clean air in surgica l

operat ing r o o m s is defined a s f i r s t a i r emi t ted f rom the final bac t e r i a l

f i l t e r ) a i rf low, i n i tself , h a s a favorable influence on the incidence of s u r -

g ica l wound infections. !' The committee!^ s t a t emen t goes on to s ay that

control led s tudies of the effect of c lean a i r f a c t o r s on wound infection r a t e s

a r e n e c e s s a r y before the p rope r u s e of spec i a l a i r -handl ing s y s t e m s for

opera t ing r o o m s c a n be defined. It notcs that p re sen t s t anda rds of a sep t i c

opera t ing protocol m u s t be maintained r e g a r d l e s s of the air-handl ing s y s t c n ~

employed. However, i t does point to the advisabi l i ty of conrridering a i r -

handling methods that may reduce a i r b o r n e ii:fections (e . g . , I I E P A f i l t ra t ion

s y s t e m s and a i r p rof i les and r a t e s of change 1 for new construct ion. In con-

clusion the commi t t ee ' s r epo r t emphas i zes that a l t e rna t e (o ther than new o r

spec i a l a i r -handling s y s t e m s methods should be cons idered in thc improvc -

ment , where clcemed n e c e s s a r y , of the microbio logica l envi ronment of the

operat ing room, T h c s c s t a t emen t s of caution by the Amer i can College of

Surgeons ref lect quite accu ra t e ly the p r e s e n t knowledge concerning clean

room s y s t e m s in the operat ing room.

E . CONCLUSIONS

It will r e q u i r e a l a rge , control led study to d i r ec t ly evaluate , in a

s ta t i s t ica l ly significant manne r , the effect of the c lean r o o m on the incidence

of postoperat ive s u r g i c a l wound infection. However, per t inent da ta d o e x i r t

that point t o the value of a reduced leve l of opera t ing r o o m a i r b o r n e m i c r o -

b ia l contamination in lowering the incidence of wound infection f o r ce r t a in

su rg i ca l s i tuat ions.

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NASA- If1 - Coml , 1.A. . C o l ~ f