MRSA in meat in Louisiana: pig meat, human strain

On Nov. 3, I posted on an enterprising group of TV stations in the Pacific Northwest who had retail meat in four states tested for MRSA. I said at the time that it was the first finding of MRSA in meat in the US that I knew of.

Turns out that I was wrong by three days. On Oct. 31, the journal Applied and Environmental Microbiology published an electronic version of a study that they will be printing in the paper journal on some future date. Journals do this when a finding is so important or timely that it should see the light immediately, rather than wait through the additional weeks or months of print production.

And this finding is certainly timely. Shuaihua Pu, Feifei Han, and Beilei Ge of the Louisiana State University Agricultural Center have made what appears to be the first scientifically valid identification of MRSA in retail meat in the United States. But — and this is an important point — it is not the swine strain, ST 398, that has been found in meat in Canada and Europe, and in hospital patients in Scotland and the Netherlands, and in pigs in Iowa; and in humans in New York, though that strain was drug-sensitive.

Instead, what the researchers found (in 5 pork and 1 beef samples, out of 120 bought in 30 grocery stores in Baton Rouge, La. over 6 weeks in February-March 2008) was USA300, the dominant community MRSA strain, and USA100, the main hospital-infection strain. In other words, they found meat that had been contaminated during production by an infected or colonized human, not by a pig. As they say:

...the presence of MRSA in meats may pose a potential threat of infection to individuals who handle the food. ... (G)reat attention needs to be taken to prevent the introduction of MRSA from human carriers onto the meats they handle and thereby spreading the pathogen.

As we've discussed before, the primary danger from MRSA in meat is not that people will take the bug in by mouth (though that is a danger, since S. aureus because of its toxin production can cause severe foodborne illness — and these researchers found, overall, an S. aureus contamination rate of 46% of their pork samples and 20% of their beef samples). Rather, the danger is that people handling the raw meat will be careless in preparing it, and will colonize themselves by touching the meat and then touching their own noses or mucous membranes, leading to a possible future infection. As reader Rhoda pointed out in a comment last week, people could also infect themselves directly, by getting MRSA-laden juice or blood into an abrasion or cut.

So: Be careful in the kitchen, keep meat separate from other foods, wash cutting boards and knives, and (say it with me, now) wash your hands, wash your hands, wash your hands.

The cite for the new paper: Pu, S. et al. Isolation and Characterization of Methicillin-Resistant Staphylococcus aureus from Louisiana Retail Meats. Appl. Environ. Microbiol. doi:10.1128/AEM.01110-08. Epub ahead of print 31 Oct 08.

Housekeeping note: This is the 16th post I've written on MRSA in food animals and/or meat. Providing all the links to the previous posts is starting to obstruct the new news. So if you are looking for all those past posts, go to the labels at the end of this post, below the time-stamp, and click on "food." You should get something that looks like this.