Staphylococcus AureusColonization and the Risk of Infection in Critically Ill Patients

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Abstract
Objective: To evaluate the relationship betweenStaphylococcus aureusnasal and tracheal colonization and infection in medical intensive care unit (MICU) patients. The primary outcome was the incidence ofS. aureusinfection in colonized versus non-colonized patients.Design: Prospective, observational cohort study. Patients admitted to the MICU during the study period were screened forS. aureusnasal and tracheal colonization by culture and a PCR assay twice weekly. Demographic, clinical, and microbiologic data were collected in the MICU and for 30 days after discharge. PFGE and antibiotic susceptibility testing were performed on allS. aureusnasal, tracheal, and clinical isolates.Results: Twenty-three percent of patients (47 of 208) were nasally colonized withS. aureus. Twenty-four percent of these patients developedS. aureusinfections versus 2% of noncolonized patients (P< .01). Nine of 11 patients with both nasal colonization and infection were infected by their colonizing strain. Two of 47 nasally colonized patients developed an infection with a different strain ofS. aureus. Fifty-three percent of intubated patients with nasal colonization (10 of 19) had tracheal colonization withS. aureusas opposed to 4.9% of intubated, non-colonized patients (3 of 61) (P< .01). Parenteral antibiotics were ineffective at clearing nasal colonization. PCR detectedS. aureuscolonization (nasal and tracheal) within 6.5 hours with a sensitivity of 83% and a specificity of 99%.Conclusions: The incidence ofS. aureusinfection was significantly elevated in nasally colonized MICU patients. Techniques to rapidly detect colonization in this population may make targeted topical prevention strategies feasible. (Infect Control Hosp Epidemiol 2005;26:622-628)

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