Etiology of community-acquired pneumonia: Impact of age, comorbidity, and severity

The aim of this study was to determine the etiology of community-acquired p neumonia (CAP) and the impact of age, comorbidity, and severity on microbia l etiologies of such pneumonia. Overall, 395 consecutive patients with CAP were studied prospectively during a 15-mo period. Regular microbial investi gation included examination of sputum, blood culture, and serology. Samplin g of pleural fluid, transthoracic puncture, tracheobronchial aspiration, an d protected specimen brush (PSB) sampling were performed in selected patien ts. The microbial etiology was determined in 182 of 395 (46%) cases, and 22 7 pathogens were detected. The five most frequent pathogens were Streptococ cus pneumoniae (65 patients [29%]), Haemophilus influenzae (25 patients [11 %]), Influenza virus A and B (23 patients [10%]), Legionella sp. (17 patien ts [8%]), and Chlamydia pneumoniae (15 patients [7%]). Gram-negative enteri c bacilli (GNEB) accounted for 13 cases (6%) and Pseudomonas aeruginosa for 12 cases of pneumonia (5%). Patients aged < 60 yr were at risk for an "aty pical" bacterial etiology (odds ratio [OR]: 2.3; 95% confidence interval [C I]: 1.2 to 4.5), especially Mycoplasma pneumoniae (OR: 5.3; 95% CI: 1.7 to 16.8). Comorbid pulmonary, hepatic, and central nervous illnesses, as well as current cigarette smoking and alcohol abuse, were all associated with di stinct etiologic patterns. Pneumonia requiring admission to the intensive c are unit was independently associated with the pathogens S. pneumoniae (OR: 2.5; 95% CI: 1.3 to 4.7), gram-negative enteric bacilli, and P. aeruginosa (OR: 2.5; 95% CI: 0.99 to 6.5). Clinical and radiographic features of "typ ical" pneumonia were neither sensitive nor specific for the differentiation of pneumococcal and nonpneumococcal etiologies. These results support a ma nagement approach based on the associations between etiology and age, comor bidity, and severity, instead of the traditional syndromic approach to CAP.