Understanding the introduction and circulation of environmental methicillin-resistant Staphylococcus aureus in a large academic medical center during a nonoutbreak, year-long period.

Background: Methicillin-resistant Staphylococcus aureus (MRSA) is a leading cause of health care-associated infections, and the role that the hospital environment might play in the transmission cycle remains undefined. We determined the distribution of environmental MRSA isolates, studied contamination patterns of MRSA clones, and evaluated the association between MRSA patient load and environmental contamination.

Methods: High-contact surfaces were sampled for 12 consecutive months in 2 inpatient wards. Concurrently, aggregated data of MRSA patient infection burden were analyzed. Antimicrobial susceptibility testing and molecular epidemiologic tools were used to characterize and analyze all isolates.

Results: Overall, 23.7% of the surfaces were MRSA positive. Handrails (58.3%), the medicine room (50.0%), chart holders (41.7%), and access doors (33.3%) were the most contaminated surfaces. Thirty-four different MRSA pulsotypes were identified. Forty-six percent of the isolates were SCCmecII/USA100. Recurrent introduction and reintroduction of clones and hot spot surfaces frequently contaminated with different MRSA strains were observed. However, long-term contamination (maintenance) was not observed. The burden of clinical MRSA cases was not an indicator of the level of environmental contamination.

Conclusions: MRSA frequently contaminates hospital surfaces during nonoutbreak periods and is not associated with the number of clinical MRSA cases. Monitoring and thorough cleaning and disinfection of hot spot surfaces are necessary to minimize the presence of MRSA in the hospital.