Nasal carriage of Staphylococcus aureus and cross-contamination in a surgical intensive care unit: efficacy of mupirocin ointment

Abstract

A six month prospective study was carried out in a surgical intensive care unit (SICU) of a university hospital to assess the incidence and routes of exogenous colonization by Staphylococcus aureus. A total of 157 patients were included in the study. One thousand one hundred and eleven specimens (nasal, surgical wound swabs, tracheal secretions obtained on admission and once a week thereafter, and all clinical specimens) were collected over a four month period from patients without nasal decontamination (A). They were compared with 729 specimens collected over a two month period from patients treated with nasal mupirocin ointment (B). All S. aureus strains were typed by restriction fragment length polymorphism (RFLP) pulsed-field gel electrophoresis after SmaI macrorestriction. The nasal colonization rates on admission were 25·5 and 32·7% in groups A and B, respectively. Thirty-one untreated patients (31·3%) and three patients (5·1%) treated with nasal ointment, acquired the nasal S. aureus in the SICU ( P = 0·00027). Nasal carriers were more frequently colonized in the bronchopulmonary tract (Bp) and surgical wound (Sw) (62%) than patients who were not nasal carriers (14%) ( P < 0·00001). The patterns were identical for nasal, Bp and Sw strains from the same patient. RFLP analysis characterized seven epidemic strains of methicillin-resistant S. aureus (MRSA) which colonized 60% of group A and 9% of group B patients ( P < 0·00001). The bronchopulmonary tract infection rate was reduced in group B ( P = 0 · 032). In conclusion, in an SICU, nasal carriage of S. aureus appeared to be the source of endogenous and cross-colonization. The use of nasal mupirocin ointment reduced the incidence of Bp and Sw colonization, as well as the MRSA infection rate.