Polymerase chain reaction-based active surveillance of MRSA in emergency department patients Masafumi Seki,1,2,* Hiroki Takahashi,3,* Norihisa Yamamoto,1 Shigeto Hamaguchi,1 Masahiro Ojima,3 Tomoya Hirose,3 Kazuhisa Yoshiya,3 Hiroshi Ogura,3 Takeshi Shimazu,3 Kazunori Tomono1 1Division of Infection Control and Prevention, Osaka University Hospital, Suita, Osaka, Japan; 2Division of Infection Control and Prevention, Tohoku Pharmaceutical University Hospital, Sendai, Japan; 3Department of Traumatology and Acute Critical Medicine, Osaka University Hospital, Suita, Osaka, Japan  *These authors contributed equally to this work Abstract: Conventional culture methods to detect methicillin-resistant Staphylococcus aureus (MRSA) take a few days, and their sensitivity and usefulness also need to be improved. In this study, active screening was performed using the polymerase chain reaction (PCR) for colonization with MRSA on admission and follow-up surveillance after admission to an emergency department between June 2012 and August 2012, and the backgrounds of PCR and/or culture-method-positive patients were compared. Among 95 patients, 15 (15.8%) patients were positive for MRSA on PCR and/or culture; 6.3% (6/95) of patients were positive on admission, and 9.5% (9/95) became positive during the stay after admission. The major primary diagnoses in MRSA-positive patients were trauma and cerebrovascular diseases. Nine (60%) of 15 patients were MRSA-positive on both PCR and culture, compared with three (20%) of 15 who were PCR-positive but culture-negative. The other three (20%) of 15 patients were PCR-negative but culture-positive. Furthermore, there was a tendency for younger age and shorter stay to be associated with PCR-positive but culture-negative results. These findings suggest that active surveillance with PCR may be highly sensitive and useful for the early diagnosis of MRSA colonization to prevent nosocomial transmission from the emergency department to the regular inpatient wards of the hospital. Keywords: active surveillance, length of stay, nosocomial transmission, BD GeneOhm MRSA assay, sensitivity, specificity