MRSA spotted on small US pig farms

By Sarah Guy, medwireNews Reporter

Routine surveillance at small pig farms may be necessary, say researchers who identified both human and animal serum samples colonized with methicillin-resistant Staphylococcus aureus (MRSA) at such locations.

The findings revealed that just over half of the 35 farms in Connecticut, USA, contained S. aureus-colonized humans and animals during the year-long sampling period.

Staphylococcal protein A gene (spa)-type analysis also revealed a similarity between a human and a pig strain of MRSA, indicating the likelihood of inter-species transmission. The same strain was also found at another farm.

"Interestingly, these farms fed pigs processed garbage," note Lynda Osadebe (Yale University, New Haven, Connecticut) and co-workers, "which may need to be explored in future research."

Nasal samples from 263 pigs and throat and nasal samples from nine humans were analyzed for the study, as well as an assessment form and questionnaire filled out by the farm workers to indicate husbandry practices and personnel protective equipment.

Overall, 15 farms had methicillin-resistant S. aureus-positive animals and five farms had either human- or animal-positive MRSA samples, giving an overall prevalence of 51%.

The majority of farms used commercially made feed (71%), while a respective 20% and 5% fed the animals processed grain and garbage. Statistical analysis indicated a significant association between feeding garbage (from local restaurants) and colonization with S. aureus.

Analysis also showed that colonized pigs were four times more likely to come from large (n=50-99) compared with small (n=<25) farms, and that of those that were positive for S. aureus, the majority (65%) were adult animals (>28 weeks old).

Human study participants were an average of 56 years old, and handled pigs for an average of 4 hours per day. Two men from two different farms were positive for MRSA, "highlighting the importance of taking both nasal and throat swabs" note Osadebe et al.

Colonized farm workers were more likely to have been hospitalized or live with someone who had been hospitalized in the previous 12 months, both factors that increase the risk for MRSA colonization, write the researchers in Zoonoses and Public Health.

"All participants wore the basic clothing: cloth gloves, rubber boots and designated farm shoes," they note; however, in general, they were "more worried about pig bites than acquiring infection."

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