We previously assessed MRSA transmission dynamics among close household contacts (HC) in households with a colonized MRSA index case (IC). Body sites and environmental samples were routinely cultured for MRSA and MSSA. The MSSA results are reported here.
Households were selected based on having a MRSA colonized IC and ≥one consenting close HC. Baseline surveys were completed and surveillance cultures collected from nose, rectum, throat, and skin monthly for 3 months. Environmental samples were taken in 8 pre-specified high use locations and pets were swabbed if identified. Cultures were performed using broth enrichment and both Chromogenic Staph and Denim Blue agar.
MSSA colonized 36% (65/183) of enrolled HC sometime over the 3 months, which was significantly greater than the rate for enrolled IC (10%, 10/99, P<0.001). At baseline, 51/182 (28%) HC were MSSA colonized. Among the 90 HC not colonized at baseline and had ≥1 subsequent visit(s), 13 (14%) converted to positive during follow-up visits. Of the 90 HC who were visited all 4 times, 29 (32%) were intermittent (1-3 positive visits) MSSA carriers, while 14 (15%) were persistently MSSA positive at all 4 visits. MSSA colonization among HC was greater (32% vs. 19%, P=0.004) in HC visit episodes where the HC was not MRSA colonized than in episodes where the HC was colonized (simultaneously or within 3 months) with MRSA. Among MSSA colonized HC, the sensitivity of throat (66%), or nasal swabs (51%) was significantly greater than rectal (20%) or axilla (8%). Screening at multiple sites improved detection: nasal+rectal+throat: 92%, nasal+throat: 88%, nasal+rectal+forearm: 71%, nasal+rectal: 62%. One-third of HC with MSSA were also colonized with MRSA over the 3 months. MSSA colonized 3/46 (7%) pets. Less than 1% of environmental swabs were MSSA positive.
MSSA colonization disproportionately affects MRSA negative household members, suggesting MSSA carriage may protect against MRSA acquisition. Pets may also be colonized. Screening at multiple body sites improves MSSA detection, especially when throat is included. Throat swabs better detected MSSA than any other site. A limitation of this study is the lack of MSSA strain subtyping, which could provide further insights on their transmission patterns.
A. Faheem, None
A. Mcgeer, None
M. P. Muller, None
K. Ostrowska, None
V. Porter, None
D. Richardson, None
A. E. Simor, None
K. Katz, None