MRSA and Animal Agriculture: A Need to Understand the Public Health Impact

• Background
• What KAW Is Doing
• What You Can Do
• Scientific Evidence

Background
Methicillin-resistant Staphylococcus aureus (MRSA) is a type of bacteria that is resistant to certain antibiotics. These antibiotics include methicillin and other more common antibiotics such as oxacillin, penicillin and amoxicillin. MRSA infections are usually skin infections, such as abscesses, boils, and other pus-filled lesions. In older adults and people who are ill or have weakened immune systems, ordinary staph infections can cause serious illness.

A study published in October of 2007 in the Journal of the American Medical Association (JAMA) (Klevens et al. 2007) estimated there were almost 100,000 U.S. cases of invasive methicillin-resistant Staphylococcus aureus (MRSA) infections in 2005 leading to nearly 19,000 deaths. In comparison, HIV/AIDS killed 17,000 people that year. These unexpectedly high numbers combined with a number of school outbreaks have propelled MRSA into the news and made many people aware that it is a serious public health problem.

What many people do not know is that MRSA has also been traced to animals raised for food production, especially pigs. These animals are often fed antibiotics at low doses for disease prevention and growth promotion, creating perfect conditions for antibiotic resistance to flourish. One Dutch study from 2007 found that 11% of pigs from 31 farms were positive for MRSA with antimicrobial medication of pigs a risk factor (van Duijkeren et al. 2007).

A study published in Veterinary Microbiology in October of 2007 has found MRSA prevalent in Canadian pig farms and pig farmers, pointing to animal agriculture as a source of the deadly bacteria. The Veterinary Microbiology study (Khanna et al. 2007) is the first to show that North American pig farms and farmers commonly carry MRSA. The study looked for MRSA in 285 pigs in 20 Ontario farms. It found MRSA at 45% of farms (9/20) and in nearly one in four pigs (71/285). One in five pig farmers studied (5/25) also were found to carry MRSA, a much higher rate than in the general North American population. Two different types of MRSA were detected in the Canadian pigs. One strain ST398 has been found mainly in pigs and in people that work with them. The other strain USA100 was one of the most common causes of MRSA infections in people in the U.S. and Canada. Both types of MRSA have caused serious infections in people.

Even more significant, a pilot study published in January 2009 by researchers at the University of Iowa reported a high prevalence of MRSA in swine (49%) and swine workers (45%) on a commercial confinement operation with farms scattered in Iowa and Illinois (Smith et al. 2009). The study is the first to demonstrate the presence of the dangerous MRSA strain ST 398 in the U.S. These results add to the mounting body of evidence that prove farms to be reservoirs for antibiotic resistant strains of MRSA.

Until recently, conventional wisdom had MRSA pegged as an opportunistic infection occurring mainly in hospitals. The JAMA study referenced above found that even healthy people are developing MRSA infections. The Veterinary Microbiology studies and the University of Iowa results in the U.S. point to pig farms as a community source of MRSA, demonstrating the need for the United States government to start systematic testing of its livestock for MRSA as well as determining if livestock strains of MRSA are present in U.S. hospitals.

What KAW Is Doing
KAW believes that identifying and controlling community sources of MRSA is a public health priority of the first order. As described above, results from a University of Iowa study demonstrate that MRSA has been found in U.S. hogs and in workers on those hog farms. However, we do not know the full extent of the problem as the U.S. government is not systematically testing U.S. livestock for MRSA. Read more in the Seattle Post Intelligencer about the lack of testing.

To address this problem, KAW first has propelled the issue of MRSA and animal agriculture into the mainstream media, educating both the public and key policymakers about the links between MRSA and livestock, as well as the need for sampling of U.S. pigs and pig farmers. Search our News page for the latest articles, editorials, and letters to the editor on this topic. Read KAW press releases here

Second, KAW currently is calling for Congress to compel the U.S. Food and Drug Administration (FDA) to study whether the use of human antibiotics in animal agriculture is contributing to the reported surge in MRSA infections and deaths in the United States. KAW continues to work on introducing language to appropriation bills that would ensure that the relevant government agencies-CDC, USDA, FDA-have enough funding and can begin to monitor for MRSA in food animals and retail meat. In February 2008, KAW urged Secretary Leavitt of the Department of Health and Human Services (HHS) to devote a portion of their funding for MRSA to the investigation of the prevalence of MRSA in U.S. animal production. In April, the director of the Agency for Healthcare Research and Quality responded that an Inter-Agency MRSA Initiative Committee is currently developing a work plan to address the prevention, diagnosis, and treatment of MRSA.

KAW also wrote a letter to the (then) Commissioner of the FDA, Andrew von Eschenbach, and the (then) Director of the Center for Veterinary Medicine (CVM) of the FDA, Stephen Sundlof. This letter addresses the need for MRSA testing as well as KAW's continued opposition to the approval of the cattle drug cefquinome, two areas in which the FDA has become unresponsive to the public interest. FDA produced the following response. As additional research comes to light on the prevalence of MRSA in U.S. livestock, KAW will continue to press for the relevant government agencies to begin systematic testing, as well to make sure there is sufficient funding to do so.

What You Can Do

• Continue to learn about this emerging issue as we update this page with the latest news and KAW actions on MRSA and animal agriculture
• Join our online action network!
• Contact your representatives in Congress and urge them to sponsor PAMTA, a bill which would reduce the inappropriate use of antibiotics in animal agriculture within two years.
• Share Your Experience. If you or a family member has been ill with an antibiotic-resistant infection, please fill out our confidential form. Please keep in mind that we cannot provide treatment or medical expertise to you.

Scientific Evidence

• de Neeling et al. 2007. High prevalence of methicillin-resistant Staphylococcus aureus in pigs. Veterinary Microbiology 122:366-372. Eighty-one percent of Dutch pig farms had pigs carrying MRSA and 39% of pigs at slaughter carried MRSA. All MRSA were tetracycline resistant and many of the bacteria were resistant to other antibiotics.
• Ekkelenkamp et al. 2006. Endocarditis due to methicillin-resistant Staphylococcus aureus originating from pigs [Article in Dutch]. Nederlands tijdschrift voor geneeskunde 150:2442-2447. A 63-year-old transplant patient was admitted with endocarditis due to pig strain ST398.
• Hanselman et al. 2006. Methicillin-resistant Staphylococcus aureus colonization in veterinary personnel. Emerging Infectious Diseases 12(12):1933-1938. Available from EID. Veterinarians averaged 7% MRSA colonization, with large animal veterinarians 16% and small animal veterinarians 4% colonization. No MRSA was detected in non-veterinarians.
• Huijsdens et al. 2006. Community-acquired MRSA and pig farming. Annals of Clinical Microbiology and Antimicrobials 5: 26-29. Mother developed MRSA mastitis and 3 family members, 3 co-workers, and 8 of 10 pigs tested positive.
• Khanna et al. 2007. Methicillin-resistant Staphylococcus aureus colonization in pigs and pig farmers. Veterinary Microbiology doi:10.1016/j.vetmic.2007.10.006. The prevalence of MRSA colonization in farms in Ontario, Canada, was 45%.
• Klevens et al. 2007. Invasive methicillin-resistant Staphylococcus aureus infections in the United States. JAMA 298:1763-1771. In 2005, there were an estimated 100,000 MRSA infections, and nearly 19,000 deaths.
• Smith TC, Male MJ, Harper AL, Kroeger JS, Tinkler GP, et al. 2009 Methicillin-Resistant Staphylococcus aureus (MRSA) Strain ST398 Is Present in Midwestern U.S. Swine and Swine Workers. PLoS ONE 4(1): e4258 doi:10.1371/journal.pone.0004258
• van Duijkeren et al. 2007. Transmission of methicillin-resistant Staphylococcus aureus strains between different kinds of pig farms. Veterinary Microbiology. Eleven percent of pigs from 31 farms were positive for MRSA with antimicrobial medication of pigs a risk factor.
• van Loo I, et al., 2007. Emergence of methicillin-resistant Staphylococcus aureus of animal origin in humans. Emerging Infectious Diseases, 2007 Dec. MRSA from an animal reservoir is now responsible for more than 20 percent of all human MRSA infections in the Netherlands.
• van Rijen, M.M.L. et al., 2008. Increase in a Dutch Hospital of Methicillin-Resistant Staphylococcus aureus Related to Animal Farming. Clinical Infectious Diseases. Vol. 46. Patients who reported exposure to pigs and calves carry a risk [for MRSA carriage] that is 1000 times higher than that of the general population in The Netherlands.
• Voss et al. 2005. Methicillin-resistant Staphylococcus aureus in pig farming. Emerging Infectious Diseases 11:1965-1966. Pig farmers had 760 times as much MRSA as patients admitted to hospital. Transmission was demonstrated between pig and farmer, family members, and nurse and patient in hospital.
• Witte et al. 2007. Methicillin-resistant Staphylococcus aureus ST398 in humans and animals, Central Europe. Emerging Infectious Diseases 13(2):255-258. Described human infections, skin, wound, and 3 nosocomial pneumonia infections with MRSA strain ST398.