High prevalence of carriage of methicillin-resistant Staphylococcus aureus at hospital admission in elderly patients: implications for infection control strategies.

Background: Despite contact isolation precautions for patients with methicillin-resistant Staphylococcus aureus (MRSA), MRSA infections are increasing in many countries.
Objective: To evaluate the role of a potential unrecognized reservoir of MRSA carried by patients in acute care wards, we determined the prevalence of MRSA at hospital admission, with special emphasis on screening-specimen yields.
Setting: A 1100-bed teaching hospital in Paris, France.
Methods: Nasal screening cultures were performed at admission to a tertiary-care teaching hospital for patients older than 75 years.
Results: MRSA was isolated from 63 (7.9%) of 797 patients. On the multivariate analysis, variables significantly associated with MRSA carriage were presence of chronic skin lesions (adjusted odds ratio [AOR], 5.10; 95% confidence interval [CI95], 2.52-10.33); transfer from a nursing home, rehabilitation unit, or long-term-care unit (AOR, 4.52; CI95, 2.23-9.18); and poor chronic health status (AOR, 1.80; CI95, 1.02-3.18). Without admission screening, 84.1% of MRSA carriers would have been missed at hospital admission and 76.2% during their hospital stay. Furthermore, 81.1% of days at risk for MRSA dissemination would have been spent without contact isolation precautions had admission screening not been performed.
Conclusions: MRSA carriage at hospital admission is far more prevalent than MRSA-positive clinical specimens. This may contribute to failure of contact isolation programs. Screening cultures at admission help to identify the reservoir of unknown MRSA patients.