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

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).

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.

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.

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).

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.