RESUMO
BACKGROUND: Methicillin-resistant Staphylococcus aureus (MRSA) is the most common nosocomial pathogen, which is particularly prevalent in intensive care units (ICUs). We performed this study to investigate the modes of transmission of MRSA and the role of nasal carriage of MRSA to subsequent MRSA infection in ICU. METHODS: From September to November 1997, all patients admitted for more than two days to the ICU were studied prospectively. Nasal swabs were obtained at admission and weekly during the ICU stay. Surveillance cultures of nares of the ICU personnels were done. Molecular typing was performed with repetitive sequence-based PCR (rep-PCR). RESULTS: At ICU admission 34 patients (21.0%: 19 MSSA, 15 MRSA) were MRSA nasal carrier, while 126 patients were free of nasal colonization. During the ICU stay 12 (9.5%: 3 MSSA, 9 MRSA) of the 126 noncolonized patients became nasal carriers (P <0.05). S. aureus infections (all MRSA) were documented in 14 (15 isolates, 8.6%) of the total 162 patients. S. aureus infections were significantly higher for those patients who were nasal carriers at ICU admission than for those found to be initially negative (P <0.05). Two different type (A, 7 isolate; B, 8 isolates) of rep-PCR patterns were identified. All four nasal and seven clinical isolates from the patients, and four nasal isolates from the ICU personnels were mixed with A and B patterns, respectively. CONCLUSION: Nasal colonization was related to the increased incidence of MRSA infections. Patients or ICU personnels who were nasal colonized with MRSA seemed to be a major source for transmission of MRSA in the ICU.