STAPHYLOCOCCUS-AUREUS NASAL CARRIAGE AS A MARKER FOR SUBSEQUENT STAPHYLOCOCCAL INFECTIONS IN INTENSIVE-CARE UNIT PATIENTS

From January to December 1994, 752 consecutive patients admitted to in tensive care units (ICU) for more than two days were studied prospecti vely for Staphylococcus aureus colonization and infection. Nasal swabs were obtained at admission and weekly during the ICU stay. At ICU adm ission 166 patients (22.1%) were Staphylococcus aureus nasal carriers, while 586 were free of nasal colonization. Of the 166 nasal carriers, 163 harbored methicillin-sensitive Staphylococcus aureus (MSSA) and t hree methicillin-resistant Staphylococcus aureus (MRSA). During the IC U stay 24 of the 586 noncolonized patients became nasal carriers (11 M SSA and 13 MRSA), and one nasal carrier initially colonized by MSSA wa s 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 high er for those patients who were nasal carriers at ICU admission than fo r those found to be initially negative (relative risk 59.6, 95% Cl 20. 37-184.32; p < 0.0001). In patients with ICU-acquired nasal colonizati on, most infections were documented prior to or at the time of the det ection of the nasal colonization; thus, in this group of patients nasa l carriage showed a Tower predictive value for subsequent Staphylococc us aureus infections than that described classically Paired isolates o f nasal colonizing and clinical strains were studied by pulsed-field g el electrophoresis (PFGE) and mecA polymorphism analysis in 30 patient s; identity was demonstrated in all but two patients. The results sugg est that, outside the setting of an outbreak of MRSA, the detection of Staphylococcus aureus nasal carriers on admission may be particularly useful in identifying those patients who are at high risk for develop ing staphylococcal infections during their ICU stay.