ETIOLOGY OF COMMUNITY-ACQUIRED PNEUMONIA - A PROSPECTIVE-STUDY AMONG ADULTS REQUIRING ADMISSION TO HOSPITAL

Background - The prevalence of microorganisms causing community-acquir ed pneumonia in patients who required admission to hospital was invest igated and the percentage of cases whose aetiology remained unknown du e to the study design and logistical problems estimated. Methods - Bet ween January 1998 and April 1993 all patients with community-acquired pneumonia admitted to six hospitals were included in the study. Aetiol ogical diagnosis, categorised as definite, probable and possible, was based on the results of routine microbiological and serological tests. Results - Three hundred and thirty four patients with a median age of 65 (range 17-92) years were enrolled in the study. The diagnosis of c ommunity-acquired pneumonia was definite in 108 cases, and probable or possible in 73 and 27 cases, respectively, including dual infections. Streptococcus pneumoniae was the predominant pathogen (27%) followed by viruses and Haemophilus influenzae (both about 8%) and Mycoplasma p neumoniae (6%). Chlamydia spp (3%) and Legionella pneumophila (2%) wer e less frequently detected. No diagnosis was made in 45% of the cases. With adjustment for antimicrobial therapy before admission and for ot her logistical considerations, it is estimated that the aetiology coul d have been ascertained in 65% of the cases. Conclusions - Streptococc us pneumoniae is the most frequently detected cause of community-acqui red pneumonia. The inability to detect a micro-organism results mainly from the use of routine diagnostic tests and, to a lesser extent, fro m logistical problems or the use of antibiotics before admission.