Numerous researchers in other countries have been reporting results on the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) in pigs and the risk of human contraction. But no U.S. agency or institution has tested MRSA patients to identify whether they carry the strain, according to the Union of Concerned Scientists, a science-based nonprofit concerned with environmental issues.
But recently researchers with the epidemiology department at the University of Iowa conducted the first test of U.S. swine for MRSA, the bacterium responsible for 94,360 infections and 18,650 deaths in the United States in 2005, a year in which MRSA killed more people than AIDs. Of the 200 pigs tested, 70 percent carried a strain of MRSA, ST398, that is known to affect humans. The researchers, led by Tara Smith, an assistant professor at the University of Iowa College of Public Health (and blogger at Aetiology), led the research team that found almost half of 20 workers on local pig farms carried the same strain of MRSA, suggesting the strain has moved up the food chain. Smith said the final report may be ready for release next week.
MRSA infections come in two forms - hospital acquired, HA-MRSA, and community acquired, CA-MRSA. People with weakened immune systems and the elderly are at most risk of HA-MRSA, according to the Mayo Clinic. CA-MRSA is responsible for serious skin and soft tissue infections and for a serious form of pneumonia.
According to a study published in the June issue of Clinical Microbiology and Infection, "Screening of pig farmers and pigs in The Netherlands has revealed that >20% of pig farmers and 39% of slaughterhouse pigs are positive for an unusual strain of methicillin-resistant Staphylococcus aureus (MRSA) belonging to sequence type (ST) 398. It is now clear that the emergence of ST398 is not just a Dutch problem, with human infections being described in several European countries, Canada and Singapore. Furthermore, some human isolates have now acquired the genes encoding Panton-Valentine leukocidin. Livestock may become an important source of community-acquired MRSA. A concerted effort on the part of clinicians, infection control practitioners and veterinarians will be required to prevent further spread of this novel strain of MRSA."
At least three people in Scotland are known to have contracted the ST398 strain, and experts are speculating that they probably contracted it from handling or eating meat. MRSA has been found in swine in the Denmark, Belgium, the Netherlands and Germany and in other farm animals such as chickens and cattle. The strain – which has caused skin infections and rare heart and bone problems in humans – is believed to have spread among pigs that were fed antibiotics to spur growth and protect them from disease.
"The recent wave of MRSA-related illnesses and deaths among otherwise healthy students and athletes is very troubling. We need to determine as soon as possible whether some of those illnesses and deaths are traceable to the overuse of antibiotics on swine farms." -Margaret Mellon, director of Union of Concerned Scientist's Food and Environment Program
The U.S. testing of swine for MRSA would -- under better circumstances -- fall under the purview of the U.S. Department of Agriculture but that agency is already under heavy fire for its negligent monitoring of cattle for bovine spongiform encephalopathy (BSE), commonly referred to as "mad cow disease" and other pathogens. A USDA official told the Seattle Intelligencer last month that the agency didn't have a test for screening imported pork.
No other federal agency, including the Food and Drug Administration, has shared any results of screening tests.
Meanwhile, the National Pork Board has said the accumulating data on MRSA and pork is "scare-mongering" and that there is "no need to avoid pork consumption or worry that pigs could make you sick as a result of MRSA."