Risk Factors for Community-Acquired Pneumonia in Adults: A Systematic Review of Observational Studies

We performed a systematic review of the literature to establish conclusive evidence of risk factors for community-acquired pneumonia (CAP). Observational studies (cross-sectional, case-control, and cohort studies) the primary outcome of which was to assess risk factors for CAP in both hospitalized and ambulatory adult patients with radiologically confirmed pneumonia were selected. The Newcastle-Ottawa Scale specific for cohort and case-control designs was used for quality assessment. Twenty-nine studies (20 case-control, 8 cohort, and 1 cross-sectional) were selected, with 44.8% of them focused on elderly subjects ≥65 years of age and 34.5% on mixed populations (participants' age >14 years). The median quality score was 7.44 (range 5-9). Age, smoking, environmental exposures, malnutrition, previous CAP, chronic bronchitis/chronic obstructive pulmonary disease, asthma, functional impairment, poor dental health, immunosuppressive therapy, oral steroids, and treatment with gastric acid-suppressive drugs were definitive risk factors for CAP. Some of these factors are modifiable. Regarding other factors (e.g., gender, overweight, alcohol use, recent respiratory tract infections, pneumococcal and influenza vaccination, inhalation therapy, swallowing disorders, renal and liver dysfunction, diabetes, and cancer) no definitive conclusion could be established. Prompt assessment and correction of modifiable risk factors could reduce morbidity and mortality among adult CAP patients, particularly among the elderly.