Potential for Pet Animals to Harbour Methicillin‐Resistant Staphylococcus aureus When Residing with Human MRSA Patients

Colonization by methicillin‐resistant Staphylococcus aureus (MRSA) may be persistent in people and is horizontally transmissible. The scientific literature suggests that domestic pets may also participate in cross‐transmission of MRSA within households. The objectives of this study were to evaluate the prevalence of and risk factors for MRSA carriage by pets residing in households with an MRSA‐infected person. From 66 households in which an MRSA‐infected patient resided, we screened 47 dogs and 52 cats using a swab protocol. Isolates from pets and humans were genotyped using two techniques and compared for concordance. Human participants completed a 22‐question survey of demographic and epidemiologic data relevant to staphylococcal transmission. Eleven of 99 pets (11.5%) representing 9 (13.6%) of households were MRSA‐positive, but in only six of these households were the human and animal‐source strains genetically concordant. Human infection by strain USA 100 was significantly associated with pet carriage [OR = 11.4 (95% CI 1.7, 76.9); P = 0.013]. Yet, for each day of delay in sampling the pet after the person’s MRSA diagnosis, the odds of isolating any type of MRSA from the pet decreased by 13.9% [(95% CI 2.6, 23.8); P = 0.017)]. It may be concluded that pets can harbour pandemic strains of MRSA while residing in a household with an infected person. However, the source of MRSA to the pet cannot always be attributed to the human patient. Moreover, the rapid attrition of the odds of obtaining a positive culture from pets over time suggests that MRSA carriage may be fleeting.