Up to 50% of cattle in infected herds are MRSA positive.
Compared with the CNR controls, the cases were more likely to have lived or worked on farms with livestock (odds ratio (OR) 35.4; 95% CI 2.7-469.8) and have been admitted to hospital (OR 11.4; 95% CI 1.4-94.8). Compared with the MRSA control group, cases were more likely to have lived or worked on farms with livestock (OR 14.5; 95% CI 2.7-76.7). Thirteen (62%) cases and no controls had come into contact with swine. The owners of the farms which cases had been in contact with were contacted with a view to testing for MRSA in the current production animals. From the farms at which the owner agreed to participate, the nares of ten randomly selected animals were sampled. A total of 23 out of 50 swine from four out of five farms tested MRSA ST398 positive. The swine isolates were indistinguishable to those from the human cases. MRSA was not detected in two cattle herds examined. Samples from swine farms were taken months, and in some instances years, after MRSA ST398 had been detected in the cases. This indicates that swine remain colonised with MRSA ST398 for substantial periods of time and thus may constitute MRSA reservoirs.
Commentary
These results constitute epidemiological and microbiological evidence that humans living or working on livestock farms, particularly swine farms, are at increased risk of MRSA infection with ST398. The health care sector should therefore be aware that zoonotic MRSA occurs. MRSA introduced into the hospital setting by persons who come into contact with swine may spread further, as is the case with other staphylococci.
