Harper AL, Ferguson DD, Leedom-Larson KR, Hanson BM, Male MJ, Donham KJ, Smith TC. An overview of livestock-associated MRSA in agriculture. Journal of Agromedicine, 15(2):101-4, 2010.

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An Overview of Livestock-Associated MRSA in
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a a b
Abby L. Harper MPH , Dwight D. Ferguson MS , Kerry R. Leedom Larson DVMMPH ,
c d b
Blake M. Hanson MA , Michael J. Male DVM , Kelley J. Donham DVM & Tara C. Smith
c
PhD
a
Department of Occupational & Environmental Health and the Center for Emerging
Infectious Diseases, University of Iowa College of Public Health, Iowa City, Iowa, USA
b
Department of Occupational & Environmental Health, University of Iowa College of
Public Health, Iowa City, Iowa, USA
c
Center for Emerging Infectious Diseases and the Department of Epidemiology,
University of Iowa College of Public Health, Iowa City, Iowa, USA
d
Department of Epidemiology, University of Iowa College of Public Health, Iowa City,
Iowa, USA
Available online: 19 Apr 2010
To cite this article: Abby L. Harper MPH, Dwight D. Ferguson MS, Kerry R. Leedom Larson DVMMPH, Blake M. Hanson MA,
Michael J. Male DVM, Kelley J. Donham DVM & Tara C. Smith PhD (2010): An Overview of Livestock-Associated MRSA in
Agriculture, Journal of Agromedicine, 15:2, 101-104
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2. Journal of Agromedicine, 15:101–104, 2010
Copyright © Taylor & Francis Group, LLC
ISSN: 1059-924X print/1545-0813 online
DOI: 10.1080/10599241003627110
WAGR
CONFERENCE FORUM
An Overview of Livestock-Associated
MRSA in Agriculture
Downloaded by [University of Iowa Libraries] at 09:23 07 December 2011
Abby L. Harper, MPH
MRSA and Farming
Dwight D. Ferguson, MS
Kerry R. Leedom Larson, DVM, MPH
Blake M. Hanson, MA
Michael J. Male, DVM
Kelley J. Donham, DVM
Tara C. Smith, PhD
ABSTRACT. Researchers, veterinary and health care practitioners, and agricultural producers gath-
ered in Johnston, Iowa, to attend the eighth annual Midwest Rural Agricultural Safety and Health
Forum (MRASH), November 2009. Among several focus areas, four plenary talks were given on the
current research being conducted examining methicillin-resistant Staphylococcus aureus (MRSA) on
swine farms in the United States. These focused on prevalence of MRSA on farms, both in swine and
in human workers; the presence of MRSA in air samples and in swine barn shower facilities; and the
Abby L. Harper and Dwight D. Ferguson are affiliated with the Department of Occupational & Environ-
mental Health and the Center for Emerging Infectious Diseases, University of Iowa College of Public
Health, Iowa City, Iowa, USA.
Kerry R. Leedom Larson is affiliated with Department of Occupational & Environmental Health, University of
Iowa College of Public Health, Iowa City, Iowa, USA.
Blake M. Hanson and Tara C. Smith are affiliated with the Center for Emerging Infectious Diseases and
the Department of Epidemiology, University of Iowa College of Public Health, Iowa City, Iowa, USA.
Michael J. Male is affiliated with the Department of Epidemiology, University of Iowa College of Public
Health, Iowa City, Iowa, USA.
Kelley J. Donham is affiliated with Department of Occupational & Environmental Health, University of Iowa
College of Public Health, Iowa City, Iowa, USA.
Ethical considerations—protection of human subjects and animals: The authors obtained University of
Iowa Institutional Review Board-01 (IRB) and Institutional Animal Care and Use Committee (IACUC)
approval for this study prior to commencement. All subjects were provided with informed consent docu-
ments and offered the chance to ask questions about the research prior to signing the consent document and
providing biological samples and questionnaire data.
This work was supported by start-up funds from the University of Iowa; the National Pork Board; and the Heart-
land Center for Occupational Health and Safety. The funding source had no influence on study design; collection,
analysis, and interpretation of data; the writing of the report; or the decision to submit the paper for publication.
Address correspondence to: Tara C. Smith, PhD, Assistant Professor, Department of Epidemiology,
Center for Emerging Infectious Diseases, 200 Hawkins Drive, C21F GH, University of Iowa, Iowa City, IA
52242, USA (E-mail: tara-smith@uiowa.edu).
101

3. 102 MRSA AND FARMING
presence of methicillin-resistant and methicillin-sensitive S. aureus in retail meats. These findings
begin to elucidate the overall picture of livestock-associated MRSA in the Midwestern United States.
KEYWORDS. Bioaerosol sampling, MRSA, Staphylococcus aureus, ST398, swine, zoonosis
Staphylococcus aureus is a common type of isolates belonged to sequence type ST398. This
bacteria that normally lives in the nasopharyn- strain was found in both pigs and pig farmers,
geal passages and sometimes on the skin. indicating that the MRSA had been shared
Although approximately one third of the popu- between animals and their caretakers in the
lation carries some strain of S. aureus, coloni- farming environment, a finding confirmed by
zation with methicillin-resistant S. aureus additional research.12–14 This documents the
(MRSA) is much less common.1 In the general importance of considering livestock and other
population, approximately 1.5% of people are animals when examining the epidemiology of
Downloaded by [University of Iowa Libraries] at 09:23 07 December 2011
colonized with MRSA.2 Although many people MRSA. Despite the research in other countries,
may carry the organism without associated ill- only one pilot study has been carried out in the
ness, it can result in clinical infection in certain United States.14
situations. In 2005, MRSA was associated with In a rural state such as Iowa, which produces
94,000 infections and 18,000 deaths.3,4 Deaths 31% of the swine raised in the United States,
from MRSA infections in the United States transmission of MRSA on swine farms could
have exceeded mortality from many other complicate efforts to reduce MRSA transmis-
infectious diseases, including human immuno- sion.14 With pork being a $5 billion a year
deficiency virus/acquired immunodeficiency industry,15 it is important to gather information
syndrome (HIV/AIDS).3,4 to assess the potential problem and determine
Although MRSA was originally recognized ways to control occupational and public health
as a concern in hospitalized patients, since the problems if they seem present. Therefore, the
mid-1990s, additional sources of MRSA have faculty and staff of the University of Iowa’s
been recognized in the community outside of Center for Emerging Infectious Diseases
hospitals (community associated, or CA-MRSA). (CEID) lab are conducting a study to examine
CA-MRSA infections typically occur in healthy the prevalence of MRSA in swine and swine
people who have not had recent health care workers from the Midwestern United States.
facility contact and are caused by strains of bac- Collaborating with Ohio State University
teria distinct from those that typically cause and the University of Minnesota, identical stud-
hospital-based infections. These bacteria have ies are being conducted to determine the preva-
caused outbreaks among athletes who share lence of MRSA in their respective region. Each
equipment, shower facilities, or personal state investigated a total of 18 farms—9
items.5 Additional CA-MRSA at-risk popula- confinement operations and 9 antibiotic-free.
tions include children in daycare facilities6,7 Samples were collected from both pigs and
and prisoners.8 Further, a newly recognized human caretakers. Producers and employees
MRSA type is livestock-associated MRSA also filled out questionnaires in order to collect
(LA-MRSA), making livestock producers a information on demographics, potential risk
newly identified risk group.9 factors, and farm production practices. To date,
The Netherlands was the first to report the samples from swine have been collected on 17
prevalence of LA-MRSA among swine farmers different farms (8 confinements, 9 antibiotic-
in 2005.10 Later studies showed farmers had an free) in Iowa and Illinois.
increased risk of infection with ST398 than the No MRSA has been found on antibiotic-free
general population,10 and that this strain now farms in Iowa to date. Overall MRSA preva-
accounted for 20% of all human MRSA cases lence in swine (confined and nonconfined pro-
in the Netherlands in 2007.11 Multilocus duction) was found to be 11%, whereas MRSA
sequence typing (MLST) showed that these in confinement swine was higher. These results

4. Harper et al. 103
indicate that colonization of swine by MRSA is operation are at a higher risk of exposure to
common on the farm systems examined, but aerosolized MRSA. How the deposition of
there is variation according to the type of pro- MRSA in the lower respiratory airways physi-
duction system. This adds to the concern about cally affects confinement operators is not yet
domestic animal species serving as a reservoir known.
of this bacterium. Humans working in confine- Because MRSA has been found in confine-
ment operations, when compared to individuals ment air samples outside the building, concern
not working in confinements, had higher preva- has arisen about MRSA as a potential environ-
lence MRSA nasal carriage. mental hazard and public health hazard.
A subset of isolates examined was negative Biosecurity is intended to stop introduction of
for the Panton-Valentine Leukocidin (pvl) gene pathogens into a system, prevent production
and found to be ST398 by MLST.14 This was losses due to existing diseases, and is key to
the first identification of ST398 in the United protecting pigs and workers. However, com-
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States. Although many human cases of ST398 mon biosecurity measures, such as showering
have been recorded in Europe, there have been in and out of the facility, may expose workers
no published cases of clinical infections with to risk factors for infection. Shower facilities
ST398 in the United States. However, from have been known to be fomites for transmission
these data, it was concluded that individuals of MRSA between athletes. Therefore, we
exposed to swine, especially in confinement hypothesized that showers in swine facilities
operations, may carry ST398, and are at could also act as fomites, facilitating transmis-
increased risk for ST398 MRSA clinical infec- sion between pork production facility workers.
tions. Further research is needed to define the We addressed the question of MRSA pres-
clinical significance of this organism in the ence in pork production shower facilities by
United States. swabbing farming facilities where swine were
Another concern in confinement operations known to be colonized with MRSA. Prelimi-
is how this organism may be passed among nary results indicate that in production systems
workers and pigs. In addition to direct contact, with MRSA-positive swine, shower stalls can
we suspected the organism may be in the air also be contaminated with MRSA. This pre-
within the buildings, creating an inhalation sents a potential challenge to biosecurity mea-
source of infection. In order to test this hypoth- sures.
esis, we conducted viable bioaerosol sampling As well as reporting the first prevalence rate
for MRSA. To evaluate the presence and partic- of MRSA among swine farmers, The
ulate size distribution of MRSA, a six-stage Netherlands16 and Italy17 reported 11.9% and
viable Andersen Cascade Impactor was used to 0.45% MRSA colonization of raw retail meat,
simulate how MRSA particles can be deposited respectively. As this has been found in live-
in the respiratory system. Additionally, the stock, questions emerged as to MRSA preva-
Andersen Cascade Impactor was used to quan- lence in meat. In Iowa, convenience samples
tify the concentration of airborne MRSA inside were taken from 22 grocery stores across Iowa,
and outside a swine confinement building. and included pork, chicken, beef, turkey, bison,
Potential health effects of aerosolized MRSA veal, hen, and lamb. Isolates that tested positive
were assessed by size distribution of particles for methicillin-susceptible Staphylococcus
into the nonrespirable and respirable size aureus had a prevalence of 16.1%. MRSA
ranges. Although the microbial concentration of prevalence was 1.1%.
MRSA detected inside the confinement opera- The emergence of MRSA in livestock repre-
tion was similar for the respirable and nonrespi- sents a novel reservoir of this pathogen, but cur-
rable ranges, the concentration of MRSA inside rently the implications of this phenomenon are
the confinement operation was higher than the unclear. Additional research needs to be carried
concentration detected outside. These results indi- out in order to determine the occupational and
cate MRSA can be deposited in the lower respira- public health risk of livestock-associated
tory airways and workers inside a confinement MRSA.

5. 104 MRSA AND FARMING
REFERENCES 9. Wulf M, Voss A. MRSA in livestock animals—an
epidemic waiting to happen? Clin Microbiol Infect.
1. Moellering RC Jr. Growing menace of community- 2008;14:519–521.
acquired MRSA. Ann Intern Med. 2006;144:368–370. 10. Voss A, Loeffen F, Bakker J, Klaassen C, Wulf M.
2. Melles DC, Tenover FC, Kuehnert MJ, Witsenboer Methicillin-resistant Staphylococcus aureus in pig farm-
H, Peeters JK, Verbrugh HA, van Belkum A. Overlapping ing. Emerg Infect Dis. 2005;11:1965–1966.
population structures of nasal isolates of Staphylococcus 11. van Loo I, Huijsdens X, Tiemersma E, de Neeling A,
aureus from healthy Dutch and American individuals. J van de Sande-Bruinsma N, Beaujean D, Voss A, Kluytmans J.
Clin Microbiol. 2008;46:235–241. Emergence of methicillin-resistant Staphylococcus aureus of
3. Flynn N, Cohen S. The continuing saga of MRSA. J animal origin in humans. Emerg Infect Dis. 2007;13:1834–1839.
Infect Dis. 2008;197:1217–1220. 12. Khanna T, Friendship R, Dewey C, Weese JS.
4. Gorwitz RJ, Kruszon-Moran D, McAllister SK, Methicillin resistant Staphylococcus aureus colonization in
McQuillan G, McDougal LK, Fosheim GE, Jensen BJ, pigs and pig farmers. Vet Microbiol. 2008;128:298–303.
Killgore G, Tenover FC, Kuehnert MJ. Changes in the 13. Huijsdens XW, van Dijke BJ, Spalburg E, van
prevalence of nasal colonization with Staphylococcus Santen-Verheuvel MG, Heck ME, Pluister GN, Voss A,
Downloaded by [University of Iowa Libraries] at 09:23 07 December 2011
aureus in the United States, 2001–2004. J Infect Dis. Wannet WJ, de Neeling AJ. Community-acquired MRSA
2008;197:1226–1234. and pig-farming. Ann Clin Microbiol Antimicrob.
5. Kazakova SV, Hageman JC, Matava M, Srinivasan 2006;5:26–36.
A, Phelan L, Garfinkel B, Boo T, McAllister S, Anderson 14. Smith TC, Male MJ, Harper AL, Kroeger JS,
J, Jensen B, Dodson D, Lonsway D, McDougal LK, Tinkler GP, Moritz ED, Capuano AW, Herwaldt LA,
Arduino M, Fraser VJ, Killgore G, Tenover FC, Cody S, Diekema DJ. Methicillin-resistant Staphylococcus aureus
Jernigan DB. A clone of methicillin-resistant Staphylococ- (MRSA) strain ST398 is present in midwestern U.S. swine
cus aureus among professional football players. N Engl J and swine workers. PLoS ONE. 2009;4:e4258.
Med. 2005;352:468–475. 15. Iowa Pork Facts. Iowa Pork Producers Association
6. Dietrich DW, Auld DB, Mermel LA. Community- Web site. Available at: http://www.iowapork.org/Newsroom/
acquired methicillin-resistant Staphylococcus aureus in PorkFacts/tabid/704/Default.aspx [accessed November 1,
Southern New England children. Pediatrics. 2004;113: 2009].
e347–e352. 16. de Boer E, Zwartkruis-Nahuis JT, Wit B,
7. Adcock PM, Pastor P, Medley F, Patterson JE, Huijsdens XW, de Neeling AJ, Bosch T, van Oosterom
Murphy TV. Methicillin-resistant Staphylococcus RA, Vila A, Heuvelink AE. Prevalence of methicillin-
aureus in two child care centers. J Infect Dis. 1998;178: resistant Staphylococcus aureus in meat. Int J Food
577–580. Microbiol. 2009;134:52–56.
8. Pan ES, Diep BA, Carleton HA, Charlebois ED, 17. Normanno G, Corrente M, La Salandra G,
Sensabaugh GF, Haller BL, Perdreau-Remington F. Dambrosio A, Quaglia NC, Parisi A, Greco G, Bellacicco
Increasing prevalence of methicillin-resistant Staphylo- AL, Virgilio S, Celano GV. Methicillin-resistant Staphy-
coccus aureus infection in California jails. Clin Infect Dis. lococcus aureus (MRSA) in foods of animal origin prod-
2003;37:1384–1388. uct in Italy. Int J Food Microbiol. 2007;117:219–222.