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David Wallinga, M.D.

Last spring, Nicholas Kristof opened eyes about the link between pigs, health and MRSA (Methicillin-resistant Staphylococcus aureus).

The piece reported on science, stronger in Europe and less well-developed in the U.S., that farms are important reservoirs for MRSA, the staph superbug that is wreaking havoc in hospitals and healthcare budgets.

We now know there is MRSA in North American pigs and on farms. What's less clear is how much this is impacting the human population now and will into the future. The big worry is that farm-associated MRSA will open another pathway for this serious infection—which is resistant to treatment from multiple antibiotics—to pop up in communities. The more farmers, farmworkers and vets carrying MRSA (or, in technical parlance, are "colonized" with MRSA), the greater the risk that its appearance in communities will occur—if not now, then eventually.

In one European study, veterinarians were found to carry farm-associated MRSA at rates several hundred times greater than the general population. Until recently, though, we had no idea whether the same problem existed in U.S. vets.

Last year, though, U.S. swine vets used the occasion of one of their own conferences to swab the nostrils of 150 volunteers. Nostrils are one place where MRSA in particular likes to hang out in humans.

The results are as follows:

Results from 37 volunteers who were not veterinary graduates (mostly students) tested negative, leaving 113 actual working vets sampled: 26 from abroad and 87 from the U.S. Of those, 7 percent of the U.S. swine vets (and a comparable percent of the foreign vets) tested positive for MRSA. This rate is about seven times greater than the rate at which we find MRSA colonized in the average American.

The particular clone, or kind, of MRSA found is important, too. In five of the vets, the MRSA found was closely related to the "livestock-associated" MRSA that we now know is widespread in Dutch and Canadian hogs and, in some cases, on pork meat.

Since this farm-associated MRSA was found on vets working in three different states, it raises concerns that this MRSA clone is widespread across U.S. hog farms. Earlier this year, a limited study in Iowa found MRSA in 45 percent of hogs sampled from two swine facilities.

Researchers from Ohio, Iowa and Minnesota are now doing more comprehensive testing to see how widespread the problem is across the country. Expect to hear more this Fall as they start reporting their results.