Background: Information is limited on the descriptive epidemiology of community-acquired pneumonia (CAP) and health care-associated pneumonia (HCAP) due to Staphylococcus aureus.
Methods: We retrospectively identified all patients admitted to a large urban US hospital between January 2005 and May 2008 with pneumonia and positive blood or respiratory cultures for S. aureus within 48 hours of admission. Patients were designated as having CAP or HCAP based on established criteria, and methicillin-resistant S. aureus (MRSA) or methicillin-susceptible S. aureus (MSSA) pneumonia based on results of initial cultures. Appropriateness of initial therapy was based on whether antibiotic coverage was provided for MRSA or MSSA.
Results: The study sample consisted of 270 patients hospitalized for S. aureus pneumonia: 142 (53%) with HCAP and 128 (47%) with CAP. Sixty-one percent of HCAP patients and 43% of CAP patients had MRSA. Demographic and clinical characteristics of MRSA and MSSA patients were similar in both CAP and HCAP. Most HCAP patients received appropriate initial antibiotic therapy (78% for MRSA and 75% for MSSA; P = 0.69); MRSA CAP patients, however, were much less likely to receive appropriate initial therapy (40% vs 59% for MSSA CAP; P = 0.05). USA100 and USA300 strains were present in 55% and 16% of all patients with MRSA HCAP; corresponding percentages for MRSA CAP were 42% and 45%, respectively.
Conclusions: Methicillin-resistant S. aureus is an important pathogen in both HCAP and CAP, and simple clinical criteria do not permit early identification of patients with MRSA versus MSSA pneumonia. Fewer than one half of patients with MRSA CAP receive appropriate initial antibiotic therapy.