A Study on Modes of Transmission and Role of Nasal Carriage to Subsequent Infection with Methicillin-Resistant Staphylococcus aureus in Medical ICU Using PFGE / 병원감염관리

ABSTRACT

BACKGROUND: In Korea, methicillin-resistant Staphylococcus aureus (MRSA) is the most common nosocomial pathogen, which is particularly prevalent in ICU. We performed this study to investigate the modes of transmission of MRSA and the role of nasal carriage of11RSA to subsequent MRSA infections in medical ICU. METHODS: All patients admitted to the medical lCU during 10 months were studied prospectively. Nasal swabs were done in all patients within 24 hours of admission and weekly thereafter. For patients who developed MRSA infections, additional cultures were done before start of antibiotics. Surveillance cultures of nostril, hands of health care workers and environment were done once at the end of the study. Bacterial typing was performed with pulsed-field gel electrophoresis (PFGE) using Smal. RESULTS: Among 138 patients enrolled, 24 patients (17.4 %) were nasal colonizers, and 9 patients (6.5%) were already infected with MRSA prior to admission. New nasal colonization among patients, in whom follow up nasal cultures were done at the interval of 3 days or more, developed at 36.2 % (21/58 patients). New infections of MRSA in patients who were admitted for more than 3 days, developed at 11.7 % (13/111 patients). Patients in isolation room were infected with MRSA less frequently (P <0.05). No other risk factors for nasal colonization of MRSA or MRSA infections were found. There were no significant differences between nasal colonizers and non-colonizers in the incidence of MRSA infections. PFGE analysis of MRSA isolates from patients showed several major patterns, which were similar in both MRSA isolates obtained prior to admission and those acquired after admission. PFGE patterns of MRSA isolates from health care workers and environment were different from those of patients. CONCLUSION: Patients who were infected or colonized with MRSA seemed to be a major source for transmission of MRSA in medical ICU. In medical lCU, where MRSA were prevalent, nasal colonization was not related to the increased incidence of MRSA infections.