Chapter Preview and Key Concepts

20InfectiousDiseasesAffecting theRespiratoryTract

On August 14, 2002, a 39-year-old male oil refinery worker inCrawford County, Illinois, visited the refinerys health unit complain-ing of a two-week cough. Later that day, the workers 50-year-oldsupervisor also visited the unit with a spastic cough, which had startedthree days earlier. Both patients were advised to see their own healthcare provider where blood samples indicated a recent infection withBordetella pertussis. The Crawford County Health Department and Illi-nois Department of Public Health were contacted because a possibleoutbreak could be brewing.

In the early parts of the 20th century, one of the most commonchildhood diseases and causes of death in the United States was per-tussis, commonly called whooping cough. Before the introduction ofa pertussis vaccine in 1940, B. pertussis was responsible for infectionand disease in 150 out of every 100,000 people. By 1980, the inci-dence, or frequency with which the disease occurs, had dropped toone in every 100,000 individuals. The vaccine had almost eliminatedthe pathogen.

Pertussis is the only vaccine-preventable childhood illness that hascontinued to rise since the 1980s with an increasing proportion of casesin adolescents and adults.Centers for Disease Control and Prevention

20.1 Structure and Indigenous Microbiota of theRespiratory System Microbial colonization is limited to the Upper

Respiratory Tract.20.2 Bacterial Diseases Affecting the Upper

Respiratory Tract Streptococcus pyogenes causes strep throat and

scarlet fever. Corynebacterium diphtheriae secretes a toxin that

inhibits protein synthesis in epithelial cells. Swelling of the epiglottis can block the trachea. Indigenous microbiota of the URT can cause

sinus infections. Infections can occur in the outer and middle ear.

20.3 Viral Infections Affecting the UpperRespiratory Tract Rhinoviruses and adenoviruses are often

responsible for the common cold syndrome. Adenovirus respiratory infections typically cause

a severe sore throat (pharyngitis).20.4 Bacterial Diseases of the Lower Respiratory

Tract Bordetella pertussis secretes toxins that destroy

cell of the ciliated epithelium. Mycobacterium tuberculosis causes a two-stage

illness. Bronchitis produces excessive mucus and a

narrowing of the bronchi. Bacterial pneumonia can be community or

hospital acquired. Some pneumonia-causing bacteria are transmitted

by dust particles or animal droppings. Bacillus anthracis spores can be inhaled in

contaminated dust.20.5 Viral Infections of the Lower Respiratory Tract

Influenza A and B viruses evolve throughantigenic drift and antigenic shift.

The paramyxoviruses are a group of virusescausing similar symptoms.MICROINQUIRY 20: Drifting and ShiftingHowInfluenza Viruses Evolve

The SARS coronavirus and Hantaviruses causeunique forms of pneumonia.

20.6 Fungal Diseases Affecting the LowerRespiratory Tract Histoplasmosis, blastomycosis, and coccidioidomycosis

affect otherwise healthy individuals. Cryptococcosis, Pneumocystis pneumonia, and

aspergillosis are escalating fungal diseases.

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CHAPTER 20 Infectious Diseases Affecting the Respiratory Tract 629

At the oil refinery, active surveillance andcase investigations were initiated by thehealth officials. Those workers with a persist-ent and spastic cough were sent to the localhospital for evaluation and interviews. Healthdepartment officials needed to know the timeof illness onset, where workers worked in therefinery, work schedule, and individuals withwhom they had close contacts. Local schoolofficials and health care providers werealerted and given guidelines on ways to rec-ognize pertussis and prevent its spread.

In the course of the epidemiologicalinvestigation, 17 cases of pertussis were iden-tified at the refinery, 15 having had closecontact with the supervisor originally diag-nosed; 7 cases occurred among the commu-nity and had no apparent relation to therefinery. In all, 21 of the cases occurred inadults 20 years of age or older. Patientsreceived an antibiotic effective against thepathogen and all recovered.

How the disease was passed from thesupervisor remains unclear. B. pertussis isspread by airborne droplets ( ).Other than an indoor, 5-minute morning meet-ing each day, work assignments were all out-doors, although workers often congregated inan indoor dining area at lunch.

FIGURE 20.1

Every 3 to 4 years, a pertussis outbreak occurs inthe United Statesand, as indicated above,many of these cases occur in adults. Althoughnearly all youngsters growing up receive the per-tussis vaccine, vaccine-induced protection doesnot last a lifetime; therefore, adolescents andadults can become susceptible to disease whenvaccine-induced immunity wanes, approxi-mately 5 to 10 years after vaccination. As aresult, college students and adults (like the refin-ery workers) may be vulnerable ( ).

Pertussis is but one of a group of infec-tious diseases affecting the respiratory tract.We will divide these diseases into two gen-eral categories. The first category will includediseases of the upper respiratory tract, suchas strep throat, diphtheria, and pertussis. Thesecond category will include diseases of thelower respiratory tract: tuberculosis, pneu-monia, and influenza. As we proceed, notethat antibiotics are available for treating thebacterial diseases while immunizations areused for protecting the community at large.

FIGURE 20.2

Bordetella pertussis. This Gram stainshows chains of small B. pertussis cells. (Bar = 10 m.) What is the Gram reaction of these stained cells?

FIGURE 20.1

300

0

600

900

1,200

1,500

1,800

2,100

2,400

2,700

3,000

Num

ber

of c

ases

60

Number of Cases of Pertussis by AgeGroupUnited States 2006. The actual number of pertussiscases (especially among adolescents [1019 years] and adults)is substantially underreported because the illness resemblesother conditions, so infected individuals might not seek med-ical care. Since 1990, the percentage of cases of adolescentsand adults has increased from 20 percent to 67 percent. Which age group accounts for the majority of cases:infants (

The respiratory system is composed of a con-ducting portion that brings oxygen to thelungs and a respiratory portion that exchangesoxygen and carbon-dioxide gasses with thebloodstream. Because air typically containsmicrobes and viruses carried on dust anddroplet nuclei, it should not be surprising thatthe respiratory system is the most commonportal of entry for these infectious agents.

Upper Respiratory Tract DefensesLimit Microbe Colonization of theLower Respiratory TractKEY CONCEPT

Microbial colonization is limited to the upper respira-tory tract.

The respiratory system is divided into theupper respiratory tract and the lower respira-tory tract ( ). The upper respira-tory tract (URT) is composed of the nose,sinus cavities, and pharynx (throat), while the

FIGURE 20.3

630 CHAPTER 20 Infectious Diseases Affecting the Respiratory Tract

lower respiratory tract (LRT) is composed ofthe larynx, trachea, bronchi, and lungs. Thelungs contain the alveoli where gas exchangeoccurs. The average adult inhales and exhalesapproximately 10,000 liters of air per day.Given that the inspired air contains microbesand microbe-laden particulate matter thatcould potentially bring microbes that causeinfection, the respiratory system has evolvedeffective defense mechanisms to minimizesuch possibilities.

During breathing, the URT and bronchiplay a critical role in filtering out foreign mate-rial, such as bacteria, viruses, and the dust par-ticles that might carry these microbes. Aprocess called mucociliary clearance involvesthe entrapment of microbes and particulatematter larger than 2 m in a layer of mucus,which is then moved by ciliated epithelial cellstoward the pharynx where it is either swal-lowed or expectorated ( ). Mucocil-FIGURE 20.4

20.1 Structure and Indigenous Microbiota of the Respiratory System

Sphenoidal sinus

Frontal sinus

Nasal cavity

Pharynx

Larynx

Trachea

Bronchi

Lungs

Diaphragm

Upperrespiratorytract

Lowerrespiratorytract

Respiratory System Anatomy. The major parts of the respiratory system are organized into the upper andlower respiratory tracts. Which part of the respiratory system would be the most susceptible to colonization andinfection?

FIGURE 20.3

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20.1 Structure and Indigenous Microbiota of the Respiratory System 631

iary clearance is supplemented by the presenceand activity of several antimicrobial sub-stances, including lysozyme and lactoferrin(see Chapter 19). In addition, an anionicantimicrobial peptide, which is active againstgram-positive and gram-negative bacteria, ispresent, along with IgA and IgG antibodies,and several human defensins (see Chapter 14).Thus, mucociliary clearance and the activity ofantimicrobial substances are largely responsi-ble for maintaining much of the LRT virtuallyfree of microbes and particulate matter.

In the nose, large particles present ininhaled air are removed by hairs in the nos-trils, while smaller particles and suspendedbacteria become trapped in the mucus cover-ing the nasal mucosa. In the posterior two-thirds of the nasal mucosa, the mucociliaryclearance also propels the mucus-entrappedparticles into