Impact of age and comorbidity on cause and outcome in community-acquired pneumonia

Abstract

Background: Prolonged life expectancy has currently increased the proportion of the very elderly among patients with community-acquired pneumonia (CAP). The aim of this study was to determine the influence of age and comorbidity on microbial patterns in patients over 65 years of age with CAP.

Methods: This study was a prospective observational study of adult patients with CAP (excluding those in nursing homes) over a 12-year period. We compared patients aged 65 to 74 years, 75 to 84 years, and > 85 years for potential differences in clinical presentation, comorbidities, severity on admission, microbial investigations, causes, antimicrobial treatment, and outcomes.

Results: We studied a total of 2,149 patients: 759 patients (35.3%) aged 65 to 74 years, 941 patients (43.7%) aged 75 to 84 years, and 449 patients (20.8%) aged > 85 years. At least one comorbidity was present in 1,710 patients (79.6%). Streptococcus pneumoniae was the most frequent pathogen in all age groups, regardless of comorbidity. Staphylococcus aureus, Enterobacteriaceae, and Pseudomonas aeruginosa accounted for 9.1% of isolates, and Haemophilus influenzae, 6.4%. All these pathogens were isolated only in patients with at least one comorbidity. Mortality increased with age (65-74 years, 6.9%; 75-84 years, 8.9%; > 85 years, 17.1%; P < .001) and was associated with increased comorbidities (neurologic; OR, 2.1; 95% CI, 1.5-2.1), Pneumonia Severity Index IV or V (OR, 3.2; 95% CI, 1.8-6.0), bacteremia (OR, 1.7; 95% CI, 1.1-2.7), the presence of a potential multidrug-resistant (MDR) pathogen (S. aureus, P. aeruginosa, Enterobacteriaceae; OR, 2.4; 95% CI, 1.3-4.3), and ICU admission (OR, 4.2; 95% CI, 2.9-6.1) on multivariate analysis.

Conclusions: Age does not influence microbial cause itself, whereas comorbidities are associated with specific causes such as H. influenzae and potential MDR pathogens. Mortality in the elderly is mainly driven by the presence of comorbidities and potential MDR pathogens.