Staphylococcus aureus colonization among household contacts of patients with skin infections: risk factors, strain discordance, and complex ecology

Background The USA300 methicillin resistant Staphylococcus aureus (MRSA) genetic background has rapidly emerged as the predominant cause of community-associated S. aureus infections in the U.S. However, epidemiologic characteristics of S. aureus household transmission are poorly understood. Methods We performed a cross-sectional study of adults and children with S. aureus skin infections and their household contacts in Los Angeles and Chicago. Subjects were surveyed for S. aureus colonisation of the nares, oropharynx, and inguinal region and risk factors for S. aureus disease. All isolates underwent genetic typing. Results We enrolled 1162 persons (350 index patients and 812 household members). The most common infection isolate characteristic was ST8/SCCmec IV, PVL1 MRSA (USA300) (53%). S. aureus colonised 40% (137/350) of index patients and 50% (405/812) of household contacts. A nares-only survey would have missed 48% of S. aureus and 51% of MRSA colonised persons. Sixty-five percent of households had .1 S. aureus genetic background identified and 26% of MRSA isolates in household contacts were discordant with the index patients’ infecting MRSA strain type. Factors independently associated (P , .05) with the index strain type colonising household contacts were recent skin infection, recent cephalexin use, and USA300 genetic background. Conclusions In our study population, USA300 MRSA appeared more transmissible among household members compared with other S. aureus genetic backgrounds. Strain distribution was complex; .1 S. aureus genetic background was present in many households. S. aureus decolonisation strategies may need to address extra-nasal colonisation and the consequences of eradicating S. aureus genetic backgrounds infrequently associated with infection.