IOWA CITY, IOWA – University of Iowa researchers have published the first study documenting methicillin-resistant Staphylococcus aureus (MRSA) in swine and swine workers in the United States. A strain of MRSA, known as ST398, was found by investigators in a swine production system in the Midwest, according to the paper published online Jan. 23 by the science journal PLoS One.

"Our results show that colonization of swine by MRSA was very common in one of two corporate swine-production systems we studied," said Tara Smith, Ph.D., associate professor of epidemiology in the UI College of Public Health and lead author of the study. "Because ST398 was found in both animals and humans, it suggests transmission between the two.

"Our findings also suggest that once MRSA is introduced, it may spread broadly among both swine and their caretakers. Agricultural animals could become an important reservoir for this bacterium," she added.

Staphylococcus aureus, often called staph, are bacteria commonly carried on the skin or in the nose of healthy people. MRSA, meanwhile, is a type of staph that is resistant to the broad-spectrum antibiotics commonly used to treat it. MRSA caused 94,000 infections and more than 18,000 deaths in the United States in 2005, according to estimates in a recent study.

MRSA has been found in a variety of animals, including horses, cattle, dogs, cats and swine. Previous studies have shown that many swine and swine farmers in Canada and the Netherlands are colonized with MRSA. However, the UI study was the first to investigate carriage of MRSA among swine and swine farmers in the United States.

"Iowa ranks first in the nation in swine production," Ms. Smith said. "Transmission of MRSA on swine farms or in veterinary facilities could complicate efforts to reduce MRSA transmission statewide and beyond."

Future studies should be conducted to assess the risk of MRSA disease among swine workers and their contacts, survey retail meat products for MRSA contamination, study larger populations of swine and humans to define the epidemiology of MRSA within swine operations and assess MRSA carriage rates in other livestock, the investigators recommended.

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