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Objective: To assess the frequency of MRSA: 1) colonization at sites other than the nares among patients (pts) on a BTU; 2) nasal colonization among BTU healthcare workers (HCW); 3) environmental contamination.
Methods: All pts admitted to the BTU had nares cultures (cxs) obtained on admission and weekly. Cxs of the throat, axillae, antecubital fossae, groins, and perianal area were obtained from 12 pts each month from 2/2009-1/2010. Nares cxs were obtained from HCWs every quarter, as were cxs of the environment. Samples were plated to CHROMagar MRSA (Becton-Dickinson). Species identification and susceptibility were done by standard microbiological methods.
Results: The mean age of the 144 pts who had cxs from multiple body sites was 52 years (range 21-87). 66% were men. 94% lived at home before they were admitted; 33.3% were admitted to the BTU from home and 41% were admitted to another unit and transferred to the BTU. The reasons for admission to the BTU included: trauma (26%), wound care (26%), and burns (22%). Of these pts, 20% had a prior history of MRSA and 17% had positive nares cxs on admission to the BTU. Age, devices, and prior operations were not associated with MRSA carriage on admission. A higher proportion of MRSA carriers than noncarriers had prior exposure to antimicrobials, but this difference did not reach statistical significance. By univariable analysis, prior history of MRSA (P < 0.0001) was associated with MRSA nasal carriage on admission. A multivariable model found male gender (odds ratio [OR] = 5.0; 95% confidence interval [95% CI] 1.4, 18.3) and admission for necrotizing fasciitis/wound care/other (OR = 4.9; 95% CI 1.7, 14.2) to be independent predictors of MRSA nasal carriage on admission. Most (11/15; 73%) pts who had MRSA at another site (1 antecubital fossa; 1 axilla; 1 groin; 1 perianal; 1 throat; 4 perianal/throat; 2 groin/perianal/throat) also carried MRSA in their nares. Only 3 (2.5%) of 119 pts who did not carry MRSA in their nares had MRSA at another site (1 groin/perianal; 1 perianal; 1 throat). The most common extra-nasal carriage sites were the throat (n = 9) and the perianal area (n = 9). Admission nares cxs were 86% (24/28) sensitive for identifying MRSA carriers and had a 96.5% (111/115) predictive value negative. Only 4/66 (6.1%) HCWs had positive nares cultures; 54 (including the 4 carriers) were screened during all 4 quarters. Of the 4 carriers, 2 carried MRSA for 1 quarter, 1 for 2 quarters, and 1 for 3 quarters. Only 4/163 (3%) environmental cxs were positive (all during the 2nd quarter). The positive sites were in the physical therapy room (mat, door handle inside the room, hand rail on steps) and the bed rail in one pt room.
Conclusions: In this BTU, pts were the major reservoir for MRSA. HCW carriage and environmental contamination were uncommon and intermittent. A single nares culture on admission identified most MRSA carriers.