- Individuals exposed to swine, especially in confinement operations, are at risk for high rates of MRSA carriage. MRSA prevalence was 31.4% in swine workers overall and 44.3% in confinement workers. - MRSA is present in U.S. swine (11% tested to date), with higher rates in confinement operations (24%). All isolates from swine and humans were the ST398 strain associated with swine farming. - Swine appear to be a reservoir for MRSA and transmission may occur between swine and exposed workers. Further study is needed to characterize strains and risks.

1. Swine workers: An emerging risk group for community-associated methicillin-
resistant Staphylococcus aureus (MRSA) 3070.0.4
Abby L. Harper, Michael J. Male, Raymond P. Scheibel, Blake M. Hanson, Tara C. Smith
Department of Epidemiology, University of Iowa College of Public Health, Iowa City, IA
ABSTRACT BACKGROUND RESULTS ANTIBIOTIC RESISTANCE PANEL
• Of those tested, all resistant to penicillin,
Over the past decade, the epidemiology of Methicillin Resistant Staphylococcus aureus – Human MRSA Prevalence by Farm oxacillin, tetracycline
methicillin-resistant Staphylococcus aureus 80.0
• MRSA is estimated to affect 94,360 people in the U.S., 75.0
(MRSA) has undergone significant changes. leading to an estimated 18,650 deaths (1) 71.5
• 3/15 also resistant to erythromycin &
70.0
Once primarily a hospital-based clindamycin
pathogen, MRSA is now found increasingly in
Percent Colonized with MRSA
• MRSA had become the most frequent cause of skin and 60.0
the community, and this bacterium has caused soft tissue infections presenting to emergency 53.6 SUMMARY
50.0
serious infections in individuals with no history departments. (5 ) 50.0
of hospitalization. Recent research has also
45.8
Humans • Individuals exposed to swine, especially in
shown that swine and swine farmers are Swine confinement operations, are at risk for MRSA
• Approximately 30% of the general population carries a 40.0
carriage
colonized with MRSA at high levels in the strain of S. aureus.
Netherlands and Canada. With Iowa raising 16 30.0
25.0
million hogs a year in a $4 billion a year • MRSA is present in U.S. swine (11% tested
• MRSA carriage rate in the general population is 20.0 16.7 to date)
industry, we set out to examine the prevalence of estimated to be approximately 1.5% (6)
MRSA in swine from Iowa and Illinois. 10.0
10.0
Therefore, we collected samples from swine on • Swine workers tested had high carriage rate
17 different farms (8 confinement, 9 antibiotic (31.4% overall, 44.3% in confinement
Methicillin Resistant Staphylococcus aureus - Swine 0.0
free) in Iowa and Illinois. To date, no MRSA has workers)
• Dutch study finds persons exposed to swine at Farm 1 Farm 3 Farm 6 Farm 9 Farm 15
been found on organic farms in Iowa. Nasal CONCLUSIONS
increased risk of MRSA carriage (3) Farms not listed were negative for MRSA.
swabs were taken from 408 swine. Overall
Farm 1: humans (15/28), swine (176/246); Farm 3: humans (9/12), swine • First identification of ST398 in the United
MRSA prevalence in swine was found to be 11% • Dutch studies confirms that swine-associated MRSA had (11/24); Farm 6: swine (4/24); Farm 9: humans (2/4); Farm 15: humans States
(45/408). MRSA prevalence in confinement recently entered the human population, and is now (1/10), swine (6/24).
swine was 24% (45/192). These results show responsible for >20% of all MRSA infections in The • Swine are a reservoir for MRSA
that colonization of swine by MRSA is very Netherlands (4)
common on the farm system we examined in the Farm 1: MRSA Prevalence in Pigs
100
100 100 • Swine strains of MRSA may be transmitted to
Midwestern U.S., adding to the concern about • Canadian study finds MRSA commonly found in pigs in 90 exposed swine workers
domestic animal species as a reservoir of this Ontario, Canada (2)
Percent of pigs colonized with MRSA
bacterium. In addition to swine, nasal and
pharyngeal swabs were taken from humans.
80 STUDY LIMITATIONS
• No data available on MRSA carriage in swine in the U.S.
Overall MRSA prevalence in humans was 34.1% 63 • This study is ongoing, additional herds need to
(27/86). Humans working in confinement 60 be sampled and further testing and
operations had a prevalence of 44.3% (27/61). 50 50 characterization of MRSA isolates needs to be
Individuals exposed to swine, especially in
STUDY QUESTIONS STUDY PROTOCOL accomplished.
confinement operations, are risk for MRSA 40 36
carriage. Additional studies are ongoing to • No human non-swine exposed controls have
examine is the prevalence of MRSA carriage in
• What the carriage rates of MRSA in rural been sampled yet.
Iowa.
specific swine herds within Iowa and Illinois? Population: 20
• Swine-exposed individuals (n=86) and various aged
• Chain of transmission is currently unknown.
• What is the prevalence of MRSA carriage in swine (n=408) from 17 herds in Iowa and Illinois.
0
swine farm workers on these same farms? 9 12 15 18 21 24 Adult FUTURE DIRECTIONS
• Further plans call for the sampling of at least 18 herds in
Age of Pig (weeks)
• Which MRSA strains are found in these Iowa and Illinois – 9 confinement facilities and 9
organic/antibiotic free farms. • More general study of MRSA in rural Iowa
populations as characterized by genotypic sub • No MRSA found to date on organic farms in Iowa
typing methods (MLST, PFGE, and SCCmec)? • All isolates examined to date were pvl negative and found to be sequence type 398 by • Population prevalence and strain types
• IRB / ICAUC approval was obtained prior to collection.
MLST
• What is the relationship between human and - Same strain as in the Dutch and Canadian studies • Animals other than swine
swine strains of MRSA in Iowa? - Also found in Denmark and Germany
Questionnaire data:
• Individuals completed questionnaires asking about swine • Overall prevalence, swine: 45/408(11%) WORKS CITED
• What are the risk factors for colonization with • Confinement swine: 45/192 (24%)
MRSA in swine workers exposed to MRSA exposure and personal protective gear and practices.
1. Klevens RM, Morrison MA, Nadle J, Petit S, Gershman K, Ray
positive swine? S, Harrison LH, Lynfield R, Dumyati G, Townes JM, Craig
SWINE WORKER RESULTS AS, Zell ER, Fosheim GE, McDougal LK, Carey RB, Fridkin SK.
• Is colonization maintained over time? Clinical specimens: Invasive methicillin-resistant Staphylococcus aureus
• Swine – Nasal swabs infections in the United States. JAMA. 2007;15:1763-71.
• Human - Nasal and throat swabs All isolates, worker and 2. Khanna T, Friendship R, Dewey C, Weese JS. Methicillin
swine, are ST398, a swine- resistant Staphylococcus aureus colonization in pigs and pig
farmers. Vet Microbiol. 2007.
farming associated strain. 3. Huijsdens XW, van Dijke BJ, Spalburg E, van Santen-Verheuvel
Laboratory Methods: This has also been found in MG, Heck ME, Pluister GN, Voss A, Wannet WJ, de Neeling
• Isolation and identification – MRSA The AJ. Community-acquired MRSA and pig-farming. Ann Clin
Netherlands, Germany, Den Microbiol Antimicrob. 2006;5:26.
– ChromAgar 4. van Loo I, Huijsdens X, Tiemersma E, de Neeling A, van de
– Catalase mark and Canada. Sande-Bruinsma N, Beaujean D, Voss A, Kluytmans J.
– Coagulase Emergence of Methicillin-Resistant Staphylococcus aureus of
Overall Animal Origin in Humans. EID. 2007;13:1834-9.
– Staph Latex 5. Moran GJ, Krishnadasan A, Gorwitz RJ, Fosheim GE, McDougal
– MRSA Latex prevalence, humans:
LK, Carey RB, Talan DA. Methicillin-resistant Staphylococcus
• PFGE using both Smal and Eagl restriction 27/86 (31.4%) aureus infections among patients in the emergency
• PVL gene via PCR department. NEJM. 2006;355:666-674.
Humans working in 6. Kuehnert MJ, Kruszon-Moran D, Hill HA, McQuillan
• spa typing via PCR and sequencing G, McAllister SK, Fosheim G, McDougal LK, Chaitram
• SCCmec type examined via multiplex PCR confinement: 27/61 (44.3%) J, Jensen B, Fridkin SK, Killgore G, Tenover FC. Prevalence of
Staphylococcus aureus nasal colonization in the United
PFGE of isolates using EagI enzyme (lanes 3-11 States, 2001-2002. JID. 2006;193:172–179. Available at:
human, 12-14 swine). Lane 15: USA100. Lane 16: http://www.journals.uchicago.edu/doi/full/10.1086/499632.
USA300. Lane 17: USA400.