Article Vol. 16, No. 5 351 Eur. J. Clin. Microbiol. Infect. Dis., 1997, 16:351-357 Staphylococcus aureus Nasal Carriage as a Marker for Subsequent Staphylococcal Infections in Intensive Care Unit Patients X. Corbella 1. , M.A. Dom/nguez 2, M. Pujol 1, J. Ayats 2, M. Sendra I , R. Pallares 1, J. Ariza 1, E Gudiol 1 From January to December 1994, 752 consecutive patients admitted to intensive care units (ICU) for more than two days were studied prospectively for Staphylococcus au- reus colonization and infection. Nasal swabs were obtained at admission and weekly during the ICU stay. At ICU admission 166 patients (22.1%) were Staphylococcus au- reus nasal carriers, while 586 were free of nasal colonization. Of the 166 nasal carriers, 163 harbored methicillin-sensitive Staphylococcus aureus (MSSA) and three methicillin- resistant Staphylococcus aureus (MRSA). During the ICU stay 24 of the 586 noncolo- nized patients became nasal carriers (11 MSSA and 13 MRSA), and one nasal carrier initially colonized by MSSA was recolonized by MRSA. Staphylococcal infections were documented in 51 (6.8%) of the total 752 patients. After 14 days of ICU stay, the prob- ability of developing staphylococcal infections was significantly higher for those patients who were nasal carriers at ICU admission than for those found to be initially negative (relative risk 59.6, 95% CI 20.37-184.32; p < 0.0001). In patients with ICU-acquired na- sal colonization, most infections were documented prior to or at the time of the detec- tion of the nasal colonization; thus, in this group of patients nasal carriage showed a lower predictive value for subsequent Staphylococcus aureus infections than that de- scribed classically. Paired isolates of nasal colonizing and clinical strains were studied by pulsed-field gel electrophoresis (PFGE) and mecA polymorphism analysis in 30 pa- tients; identity was demonstrated in all but two patients. The results suggest that, out- side the setting of an outbreak of MRSA, the detection of Staphylococcus aureus na- sal carriers on admission may be particularly useful in identifying those patients who are at high risk for developing staphylococcal infections during their ICU stay. For more than 30 years, the role of nasal carriage has been recognized in the pathogenesis of staphy- lococcal infections among patients undergoing surgery or hemodialysis (1-5). Although it seems logical to surmise the same link between staphy- lococcal nasal carriage and the development of Staphylococcus aureus infections among inten- sive care unit (ICU) patients, the epidemiology of these infections in this population has not yet been lInfectiousDiseaseService,and 2Microbiology Service,Hos- pital de Bellvitge, University of Barcelona, 08907 L'Hospitaletde Llobregat, Barcelona,Spain. well established. In a previous experience, in the setting of an outbreak of methicillin-resistant Staphylococcus aureus (MRSA), we observed that ICU patients who were nasal carriers of ei- ther methicillin-sensitive Staphylococcus aureus (MSSA) or MRSA were at high risk for the de- velopment of nosocomial staphylococcal bactere- mia (6). However, this relationship may be ques- tioned in part by the results obtained by Brun- Buisson et al. (7), in whose study the treatment with mupirocin of those ICU patients with staphy- lococcal nasal colonization did not significantly re- duce Staphylococcus aureus nosocomial infec- tions.