Eli Perencevich and colleagues at the University of Iowa continue to publish interesting work on the epidemiology of MRSA, using data their patients in the VA and their farm-state location near many animals.
In a previous study, they found that living within 1 mile of a high-density pig farm nearly doubled the risk of colonization with MRSA upon admission (ICHE, 2014 Feb;35(2):190-3). Building on that work, they now report (in Antimicrobial Resistance & Infection Control) the links between nasal colonization and MRSA clinical infections (many are colonized, but fewer are clinically sick at the moment), by genetic testing of both samples from the same patients. Paired samples like this are rarely tested.
They found that paired samples were genetically and phenotypically indistinguishable, suggesting that colonization was the source for clinical infection. The more surprising result was that classic “livestock-associated MRSA” or LA-MRSA spa types were not identified in these patients:
Livestock-associated MRSA does not appear to contribute significantly to the prevalence of MRSA colonization or the burden of MRSA infections in ICVAHCS, despite the high density of livestock in the region.
Before you (rashly) conclude that high-density pig farms are not a threat to human health, consider the alternative:
Taken together, these results suggest that swine may be a source of non-LA-MRSA colonization and infections in humans.
An excellent research question, indeed.