Risk factors for methicillin-resistant Staphylococcus aureus hospital-acquired pneumonia among surgical intensive care unit patients at an urban, level I trauma, academic medical center

Introduction: Reported prevalence of MRSA HAP and associated risk factors identified by the Infectious Disease Society of America may not apply to the previously healthy adults admitted to the SICU. Approximately 60% of our institutions SICU HAPs receive anti-MRSA therapy however MRSA comprises only 6% of SICU isolates and 15% all S. aureus isolates. Identifying risk factors for MRSA HAP among SICU patients may help define subpopulations of SICU patients with HAP who require empiric MRSA coverage.

Objectives:   Identify risk factors for methicillin-resistant Staphylococcus aureus (MRSA) among adult surgical intensive care unit (SICU) patients with culture-positive S. aureus hospital-acquired pneumonia (HAP).

Study Design: An institutional review board approved retrospective cohort study of adult patients admitted to Froedtert Hospital's 21-bed SICU from July 2007 to August 2012 was evaluated.

Methods: Eligible patients were hospitalized for ≥48 hours in the SICU with broncho-alveolar lavage (blinded or unblinded) culture-positive MRSA or methicillin-susceptible S. aureus (MSSA) HAP. Logistic regression analysis was performed to identify risk factors for MRSA HAP. Potential risk factors included age, sex, MRSA nasal colonization, ICU and hospital length of stay (LOS) prior to culture, hemodialysis, steroid administration, and receipt of antibiotics within the previous 90 days.

Results:  A total of 67 S. aureus HAPs were evaluated (MSSA, n=49; MRSA, n=18). Three risk factors were associated with isolation of MRSA: MRSA nasal colonization, LOS prior to culture, and age. MRSA nasal colonization was the most significant risk factor (OR 11.75, 95%CI 2.1-65.7, positive predictive 77%, negative predictive 79%). The risk for MRSA HAP increased by 1.27-fold for each day of hospitalization (95%CI 1.00-1.60) and 1.05-fold for each year of life (95%CI 1.00-1.10).

Conclusions: In adult SICU patients with culture-positive S. aureus HAP, MRSA nasal colonization, LOS prior to culture, and age are associated with the isolation of MRSA compared to MSSA.