An overview of livestock-associated MRSA in agriculture
This article was downloaded by: [University of Iowa Libraries]On: 07 December 2011, At: 09:23Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: MortimerHouse, 37-41 Mortimer Street, London W1T 3JH, UK Journal of Agromedicine Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/wagr20 An Overview of Livestock-Associated MRSA in Agriculture 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 2010To 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 inAgriculture, Journal of Agromedicine, 15:2, 101-104To link to this article: http://dx.doi.org/10.1080/10599241003627110PLEASE SCROLL DOWN FOR ARTICLEFull terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditionsThis article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form toanyone is expressly forbidden.The publisher does not give any warranty express or implied or make any representation that the contentswill be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug dosesshould be independently verified with primary sources. The publisher shall not be liable for any loss, actions,claims, proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly orindirectly in connection with or arising out of the use of this material.
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 ofDownloaded 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
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-Downloaded by [University of Iowa Libraries] at 09:23 07 December 2011 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.
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