Transmission of methicillin-resistant Staphylococcus aureus in an acute care hospital in Japan.

Background: Asymptomatic carriers of methicillin-resistant Staphylococcus aureus (MRSA) are important sources of nosocomial transmission. However, the route of transmission of MRSA is not completely understood. The purpose of this study was to calculate MRSA transmission rates in a hospital with a high MRSA infection/colonization density and inadequate hand hygiene compliance.
Methods: The prevalence of MRSA colonization among 157 patients at the time of admission to and discharge from a medical school hospital in Japan was determined by performing surveillance cultures. All MRSA isolates were evaluated using multilocus sequence typing (MLST) to identify the transmission routes.
Results: Methicillin-resistant S. aureus was prevalent in 1.9% of our study population. MRSA was acquired during hospitalization at a rate of 4.0/1000 patient-days. At discharge, 5.1% of the patients exhibited MRSA colonization; this was significantly higher than the prevalence noted upon admission ( P  < 0.001). MLST documented three possible nosocomial transmission events. MRSA colonization was detected using surveillance cultures prior to being identified by conventional, clinically oriented examinations.
Conclusions: Multilocus sequence typing results suggested that patients who were colonized with MRSA acquired it during hospitalization. These results reinforce the importance of infection control for preventing nosocomial MRSA transmission in hospitalized patients.