PURPOSE:Methicillin-resistant Staphylococcus aureus (S. aureus [SA]) (MRSA) is a major cause of nosocomial pneumonia. However, the burden of MRSA in non-nosocomial pneumonia (e.g., healthcare-associated pneumonia [HCAP], community-acquired pneumonia [CAP]) remains unclear.
METHODS:We retrospectively identified all patients admitted to a large, urban teaching hospital over a 3-year period with non-nosocomial SA pneumonia. Study subjects were identified based on a discharge diagnosis of pneumonia and (within 48h of admission): (1) culture (blood or sputum) evidence of SA; (2) compatible pulmonary imaging study; and (3) signs/symptoms of pneumonia. Subjects with HCAP were identified using established critieria (eg, prior hospitalization within 90d of admission, intravenous antibiotic therapy in preceding 30d, nursing home residency, hemodialysis, etc.); all remaining subjects were designated as CAP.
RESULTS:A total of 244 study subjects were identified (HCAP, n=128; CAP, n=116). MRSA accounted for 45% of all SA pneumonia in CAP vs 61% in HCAP (p=0.015). Although the appropriateness of initial antibiotic therapy was high for both groups, it was higher for HCAP patients (89% vs 70% for CAP, p<0.001). Need for mechanical ventilation and crude mortality were similar for CAP and HCAP. Fewer than 13 % of all MRSA had MIC values to vancomycin (VAN) <1 mcg/ml, and VAN MICs >2 mcg/ml were seen in 15% of those with HCAP vs. 8% of CAP subjects. USA-300 CA-MRSA strain accounted for 42% of MRSA in CAP vs 15% in HCAP (p<0.001).
CONCLUSION:MRSA is prevalent in patients with non-nosocomial pneumonia due to SA, including CAP. Few MRSA pneumonia strains have low MICs to VAN. CA-MRSA represents an emerging pathogen in both CAP and HCAP due to SA.
CLINICAL IMPLICATIONS:Physicians must consider MRSA when evaluating patients with non-nosocomial pneumonia. The changing MICs of MRSA to VAN and the prevalence of CA-MRSA in both CAP and HCAP suggest the need to examine the role for alternatives to VAN.
DISCLOSURE:Andrew Shorr, Grant monies (from industry related sources) Astellas Pharma US, Ortho-MacNeil-Jansen, Pfizer; Consultant fee, speaker bureau, advisory committee, etc. Astellas Pharma US, Ortho-MacNeil-Jansen, Pfizer; No Product/Research Disclosure Information