Methicillin-resistant Staphylococcus aureus transmission: The possible importance of unrecognized health care worker carriage

Background: This study was conducted to evaluate the ongoing transmission of methicillin-resistant Staphylococcus aureus (MRSA) in a 10-bed trauma intensive care unit (TICU) in a large teaching hospital. Methods: Surveillance cultures for MRSA were obtained on admission to the TICU. Colonized or infected patients were placed on contact precautions. On February 21, 2003, 19 burn patients were admitted to the TICU after a local mass casualty event. Universal barrier precautions were implemented for all patients, and point-prevalence surveys (nares cultures) were used to detect MRSA acquisition. Results: During March 2003, 58% of the burn patients developed MRSA infection or colonization. Six of 133 health care workers (HCWs) had positive MRSA screening cultures. Seven patients and 4 HCWs harbored the pulsed-field gel electrophoresis clone A. Two patients and 1 HCW harbored clone B. Once the colonized HCWs were successfully decolonized, a sustained reduction in MRSA infections occurred. Conclusion: Transmission of MRSA in an ICU was observed despite various infection control precautions. Identifying and treating colonized HCWs was followed by a significant reduction in the incidence of MRSA. Unrecognized MRSA-colonized HCWs may be an important reservoir in endemic institutions that could impair other control measures.