Clinical and Economic Outcomes for Patients with Health Care-Associated Staphylococcus aureus Pneumonia

While the increasing importance of methicillin-resistant Staphylococcus aureus (MRSA) as a pathogen in health care-associated S. aureus pneumonia has been documented widely, information on the clinical and economic consequences of such infections is limited. We retrospectively identified all patients admitted to a large U.S. urban teaching hospital between January 2005 and May 2008 with pneumonia and positive blood or respiratory cultures for S. aureus within 48 h of admission. Among these patients, those with suspected health care-associated pneumonia (HCAP) were identified using established criteria (e.g., recent hospitalization, admission from nursing home, or hemodialysis). Subjects were designated as having methicillin-resistant (MRSA) or methicillin-susceptible (MSSA) HCAP, based on initial S. aureus isolates. Initial therapy was designated “appropriate” versus “inappropriate” based on the expected susceptibility of the organism to the regimen received. We identified 142 patients with evidence of S. aureus HCAP. Their mean (standard deviation [SD]) age was 64.5 (17) years. Eighty-seven patients (61%) had initial cultures that were positive for MRSA. Most (∼90%) patients received appropriate initial antibiotic therapy (86% for MRSA versus 91% for MSSA; P = 0.783). There were no significant differences between MRSA and MSSA HCAP patients in mortality (29% versus 20%, respectively), surgery for pneumonia (22% versus 20%), receipt of mechanical ventilation (60% versus 58%), or admission to the intensive care unit (79% versus 76%). Mean (SD) total charges per admission were universally high ($98,170 [$94,707] for MRSA versus $104,121 [$91,314]) for MSSA [P = 0.712]). Almost two-thirds of patients admitted to hospital with S. aureus HCAP have evidence of MRSA infection. S. aureus HCAP, irrespective of MRSA versus MSSA status, is associated with significant mortality and high health care costs, despite appropriate initial antibiotic therapy.Traditionally, infections have been categorized as either community associated or nosocomial in origin. The theory supporting this dichotomy arose from observations that pathogens causing these two types of infections were distinct. However, with the spread of health care delivery beyond the confines of acute-care hospitals, patients increasingly may present to emergency departments (ED) with infections caused by organisms such as methicillin-resistant Staphylococcus aureus (MRSA). This trend has led to the evolution of the concept of health care-associated infection (HCAI). Recent studies have validated the concept of HCAI for a number of types of infection, ranging from endocarditis to pneumonia (1, 4, 10, 12). Many such reports, however, have provided scant microbiologic information and have focused more on distinctions in patient types and risk factors for resistant infection. The situation regarding limited microbiologic data is particularly acute with respect to S. aureus. Although Fridkin and colleagues, in an assessment of the national burden of MRSA, underscored the growing prevalence of this pathogen in health care-associated pneumonia (HCAP) (3), they presented little information regarding outcomes of such infections.S. aureus in general—and MRSA in particular—remains a growing challenge for both hospitals and physicians. Good infection prevention practices necessitate isolation precautions for patients with MRSA, which has made early identification of these persons a time-sensitive endeavor. Beyond infection prevention issues, which may complicate the care of patients at risk for MRSA HCAP, patients with HCAP due to either methicillin-sensitive S. aureus (MSSA) or MRSA may consume substantial resources. Further complicating management of HCAP due to S. aureus is the shift in strain types and antimicrobial resistance implicated in pneumonia (3). The USA300 strain of MRSA, for example, may produce significant toxins and may not respond well to anti-MRSA antimicrobials that are routinely employed (11). Because of these issues, physicians require data regarding the microbiology, epidemiology, and outcomes associated with HCAP due to S. aureus (both MSSA and MRSA).To address these issues, we conducted a retrospective observational study of patients in a large urban hospital with HCAP due to culture-proven S. aureus. Our aims were to describe outcomes and resource utilization among patients with S. aureus HCAP and to understand possible differences between patients with MSSA versus MRSA pneumonia. We also sought to examine differences in outcomes and resource utilization as a function of pathogen susceptibility to vancomycin and the specific strain type involved.(Preliminary findings from this study were presented at the 48th Annual Interscience Conference on Antimicrobial Agents and Chemotherapy [ICAAC]-Infectious Diseases Society of America [IDSA] 46th Annual Meeting and the 2008 annual meeting of the American College of Chest Physicians [ACCP] [1a, 10a, 11a].)