MRSA in the US Swine Industry

Recent Developments

Peter Davies, Jisun Sun, My YangCollege of Veterinary Medicine

University of Minnesota

Outline

Background of ‘livestock associated’ MRSA?

State of play - 2013 Recent UMN research

US swine veterinarians (UMASH) US pig farms (NPB – pork check off)

Recent developments in Europe and USA

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Staphylococcus aureus

Common inhabitant of warm-blooded animals ‘Normal flora’ (20-30% of people)

Common opportunistic pathogen in humans Insignificant to fatal Broad clinical manifestations Skin and soft tissue infections Invasive: pneumonia, septicemia and death Bacteremia: 80% fatality rate prior to antibiotic era

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Holland – an issue emerges!

Very low MRSA prevalence Intensive screening and typing with sma1 PFGE ‘Search and destroy’ policy – isolation/decolonization

2004: 6mo girl screened before surgery for a congenital heart defect

MRSA isolate not typable with Sma1 PFGE

2 other screening isolates not typable by Sma1 PFGE All 3 ‘cases’ epidemiologically linked to pigs

Studies of MRSA prevalence in pigs, farmers and pork

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MRSA in animals – publication rate

0

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4

6

8

10

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70s 80s 90-95

96 97 98 99 00 01 02 03 04 05 06 07

Years

Cattle

Cat, Dog

Horse

Pig, Sheep

2010>50

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S. aureus subtyping methods

PFGE

MLST

SCCmec typing (I – XI)

Spa typing Ridom

egenomics

‘Livestock associated’

Sma1 Untypable

ST398 (CC398)

III, IV, V

t034, t011, t108……...

539, ………………..…..

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LA-MRSA: more than ST398 in pigs

ST9 (t899, t337) - Asia, Italy, Spain, USA ST5 (t002) - North America (US, Canada) ST1 - Denmark, USA, Switzerland, Italy ST72 - USA, Korea ST97 – Italy, Spain ST49 – Switzerland ……

LA-MRSA: more than ST398

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ST398t011, t108

t034, t567… >30 spa

typesST5t002

ST9t899t337

Not all ‘livestock associated’ MRSA are ST398

‘Animal independent’ ST398 clinical infections in NY city (Uhlemann et al, 2012)

Studied outpatient MRSA isolates, non-invasive MSSA cases, and bloodstream MSSA isolates

ST398 t571: 5% of non-invasive MSSA; 2.5% of MSSA bacteremias

“Clinically important clone that differs significantly at the genome level from its livestock associated counterpart”

Distinct ‘pig clade’ and ‘human clade’ of ST398 t571 Only reported ST398 infections in USA are t571

MSSA without known livestock contact

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ST398 MRSA exposure riskGenerally accepted facts (2013)

ST398 occur in livestock species in many countries

High MRSA exposure risk for people with direct animal contact 20-50% prevalence in farmers ~ 0.5 - 2% in general populations

Key questions Are they truly colonized? What is the consequent risk to health?

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ST398 MRSA public health risk Generally accepted facts (2013)

Elevated occupational risk of infection not well documented

Current evidence suggests low transmissibliity No reports of outbreaks

Current evidence suggests low virulence? Significantly less invasive disease in Europe Serious infections uncommon General lack of virulence determinants Few fatalities

ST398 bacteremia cases in Denmark (Petersen pers. Comm.)

Impact low ~1% of cases Only 6 MRSA

cases Trend concerning No animal contact

in bacteremia cases

Are they livestock associated?

and how?12

ST 398 1.2% of bacteremic S. aureus

cases in 2013

Studies of S. aureus

Pilot study of ecology of S. aureus on swine farms (NPB)

Longitudinal study of S. aureus and MRSA colonization and infection in swine veterinarians NIOSH (UMASH center) 68 swine veterinarians

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Study design

18 months longitudinal study to Dec. 2013 66 swine veterinarians across 15 states

Monthly nasal swabs Survey of pig exposure and events of injury/infection

One time quantitative study Direct enumeration of CFU in nasal swabs

Prevalence of SA and MRSA in vets

t034 (ST398) , t337 (ST9), t002 and t045 (ST5) most common types Correspond with the most common variants in US pigs.

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SA : 58.3% to 82.4% MRSA : 5.9% to 15.2%

Permanent of intermittent carriage?

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Colonization patterns ofPersistent Carriers

Intermittent carriers

Do permanent carriers harbor more SA?

41 volunteers at AASV 18 PC 23 IC

Nasal swab at meeting Time since pig contact Quantitative culture

Direct plating – without enrichment

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Do persistent carriers harbor more SA?

More PC were positive 15 of 18 (83%) PC 7 of 23 (30%)

PC had more SA ‘PC’ of S. aureus occurs in a subset of swine

vets who are frequently culture positive and carry higher numbers of organisms Importance of host factors?

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S. aureus prevalence in US swine herds

Samples processed from 31 farms (of 36) 20 nasal swabs from growing pigs Collected by vets in UMASH study (1 farm per

vet) Multiple states Data on farm, including antibiotic exposure

Spa typing, MLST typing results Antimicrobial resistance and enterotoxin

production to be conducted21

Prevalence by farm

One farm S. aureus negative Only 1 farm harbored MRSA (known

positive) MLST and spa types similar in pigs and vets Vet and pig data indicate relatively low

MRSA prevalence in the US swine industry

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**

* Size of circles : Prevalence (%)

Comparison of spa types detected in veterinarians and swine

82.7% 92.4%

82.7% 92.4%

t2330 t7160 t2876 t1255 t1250 t045 t856 t062

t1430 t1334t922 t363 t8314

t2196 t008t126 t6509t330 t338

t2330 t7160 t2876 t1255 t1250 t045 t856 t062

t1430 t1334t922 t363 t8314

t2196 t008t126 t6509t330 t338

t899 t2582

t306 t899t5838 t8314t2462 t1793

t11374t11241t5462

t899 t2582

t306 t899t5838 t8314t2462 t1793

t11374t11241t5462

Veterinarians

Veterinarians PigsPigs

82.7%

92.4%

Scaremongering?

Most data indicate the public health risk of S. aureus (incl. MRSA) in the pig reservoir is minimal

Indication of increases in some EU countries Changes in screening practices Combine clinical and non-clinical cases

Lack of significant clinical infections in occupationally exposed people

Steady drum beat of publications ‘talking up’ the risk

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Schinasi et al. Environmental Health 2014 13:54

Conclusion:Moderate densities of swine ….were associated with MRSA nasal carriage detected by PCR. This finding is supported by past evidence of associations between MRSA nasal carriage and contact with swine production.

Summary

Livestock associated MRSA remains a difficult public relations issue for the swine industry

Accumulating data point to much lower prevalence than in many EU countries Swine veterinarians Pig farms

Promises to be a case study in misinformation and biased inference in science

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