Risk factors associated with potentially antibiotic-resistant pathogens in community-acquired pneumonia.

RATIONALE: To identify pathogens that require different treatments in community-acquired pneumonia (CAP), we propose an acronym, "PES" (Pseudomonas aeruginosa, Enterobacteriaceae extended-spectrum β-lactamase-positive, and methicillin-resistant Staphylococcus aureus).

OBJECTIVES: To compare the clinical characteristics and outcomes between patients with CAP caused by PES versus other pathogens, and to identify the risk factors associated with infection caused by PES.

METHODS: We conducted an observational prospective study evaluating only immunocompetent patients with CAP and an established etiological diagnosis. We included patients from nursing homes. We computed a score to identify patients at risk of PES pathogens.

MEASUREMENT AND MAIN RESULTS: Of the 4,549 patients evaluated, we analyzed 1,597 who presented an etiological diagnosis. Pneumonia caused by PES was identified in 94 (6%) patients, with 108 PES pathogens isolated (n = 72 P. aeruginosa, n = 15 Enterobacteriaceae extended-spectrum β-lactamase positive, and n = 21 methicillin-resistant Staphylococcus aureus). These patients were older (P = 0.001), had received prior antibiotic treatment more frequently (P < 0.001), and frequently presented with acute renal failure (P = 0.004). PES pathogens were independently associated with increased risk of 30-day mortality (adjusted odds ratio = 2.51; 95% confidence interval = 1.20-5.25; P = 0.015). The area under the curve for the score we computed was 0.759 (95% confidence interval, 0.713-0.806; P < 0.001).

CONCLUSIONS: PES pathogens are responsible for a small proportion of CAP, resulting in high mortality. These pathogens require a different antibiotic treatment, and identification of specific risk factors could help to identify these microbial etiologies.