MRSA in the household: Longitudinal analyses from the Community-Onset Staphylococcus aureus Household Cohort (COSAHC) Study Australia
METHODS: 291 patients with community-onset S. aureus infections were identified via specimens from a community-based pathology service (Oct 2008-Dec 2010). All MRSA and a frequency-matched random subset of methicillin sensitive S. aureus(MSSA) were followed for up to two years. Patients and household (HH) contacts provided nose and axilla swabs (a subset of 92 also provided throat and groin) and detailed demographic information, medical history, exposure history including occupation, sporting activities, pets, and HH interactions. All isolates were characterised using PFGE, MLST, spa, and pvl.
RESULTS: 729 from 291 households participated (156 initial MSSA infections, 135 MRSA). S. aureus carriage was common (64% of index cases colonised in nose and/or axilla, and 46% of HH contacts). S. aureus nasal carriage for the total sample was 47% (10% MRSA, 37% MSSA). MRSA nasal colonisation rates diminish over the two year follow-up for most strains, however some persisted in the index and contacts (WA-MRSA1 [ST1], EMRSA15 [ST22]). Despite the high prevalence in clinical isolates, WSSP (ST30) and Queensland (ST93) clones were generally absent from nose swabs collected from these households.
CONCLUSIONS: We found high colonisation rates in the nose and/or axilla for S. aureus (53%) and for MRSA (12%) but the patterns of HH colonisation are complex and variable. Some strains persist in households for up to two years whilst others were not found to ever colonise the index or contacts over the follow-up period. As the strains that do not persist tend to be thepvl positive community MRSA strains, differences in persistence and penetration in the household can guide patient and contact management.