Etiology of community-acquired pneumonia in hospitalized patients: a 3-year prospective study in Japan.

STUDY OBJECTIVE To compare the etiology of community-acquired pneumonia in Japan and Western countries, the causative pathogens were prospectively investigated in patients requiring hospitalization. DESIGN Prospective study over a 3-year period. SETTING A community general hospital in Japan. PATIENTS Three hundred twenty-six episodes of community-acquired pneumonia in 318 patients admitted to the hospital between July 1994 and June 1997. METHODS The microbiological diagnosis was based on the results of quantitative sputum culture, blood culture, and other invasive procedures, including transthoracic needle aspiration or bronchoscopic examination. Serologic tests for Mycoplasma pneumoniae, Chlamydia spp, Legionella spp, and viruses were also routinely performed. RESULTS Causative pathogens were identified in 199 episodes (61%). Streptococcus pneumoniae was the most common pathogen (23%), followed by Haemophilus influenzae (7.4%), M pneumoniae (4.9%), and Klebsiella pneumoniae (4.3%). The Streptococcus milleri group and Chlamydia pneumoniae were detected in 3.7 and 3.4% of the episodes, respectively. Pneumonia due to Legionella spp was recognized in only two patients. CONCLUSIONS The etiology of community-acquired pneumonia in Japan did not differ markedly when compared with that of Western countries except for the low incidence of Legionella pneumonia. C pneumoniae and the S milleri group, which are emerging or newly recognized pathogens, were also significant causative microorganisms.