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19-06-2012 | General practice | Article

Pets could pass on MRSA

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MedWire News: Pet dogs and cats can harbor pandemic strains of methicillin-resistant Staphylococcus aureus (MRSA) while living in houses with an infected human, creating the potential for cross-transmission, say researchers.

In a study of 66 households with a human MRSA-infected patient, 11.5% of the 99 cohabiting pets were MRSA-positive. Furthermore, six of these nine households contained genetically concordant human and animal strains of the infection.

"As the factors that promote person-pet cross-transmission are not yet clearly elucidated, pet owners should be educated regarding common sense practices to help mitigate risk," suggest Daniel Morris and Shelley Rankin from the University of Pennsylvania in Philadelphia, USA, and colleagues.

The team also report in Zoonoses and Public Health that any MRSA carriage in these animals may be fleeting, since each day of delay in sampling after the cohabiting human's positive culture resulted in a 13.9% decrease in the odds of isolating MRSA.

Almost half (48.5%) of the study participants were children aged 18 years or younger, and the majority of all human participants (74.2%) had MRSA strain type USA 300.

Conversely, the most common strain isolated in the seven (of 47) dog- and four (of 52) cat-carriers was USA 100, currently the top-ranking source of human nasal colonization of MRSA in the USA.

The research team acknowledges that this finding of nonidentical isolates in human-pet pairings could mean the pet acquired MRSA from a source other than the cohabiting human participant in the study.

Regardless of this, however, the current findings illustrate that dogs and cats harbor strains of MRSA that cause skin and soft tissue infections in humans, say Morris et al.

Multivariate analysis revealed that human infection with strain USA 100 increased the chances of pet carriage by a significant 11.4 times, while human exposure to amoxicillin-clavulanic acid (amoxi-clav) within the month prior to MRSA diagnosis increased the risk by a significant 16.6 times.

While it is unexpected to find that a patient's exposure to the antibiotic appeared to increase the risk for transmission to a pet, the researchers remark on the possibility that human exposure to amoxi-clav could be a surrogate for some unevaluated risk factor.

The team recommends that "social distancing" and hygiene practices such as preventing pets from licking infected persons, and daily washing of the pet's food and water dishes could mitigate some of the risk for cross transmission.

By Sarah Guy

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