Objective: To study the pathogens in community-acquired pneumonia (CAP), especially the prevalence of atypical pathogens.
Methods: A prospective study was performed on 103 consecutive adult patients with CAP between November 2001 and June 2002. Antibodies of the paired serum samples to Mycoplasma pneumoniae, Legionella pneumophilia, and Chlamydia pneumoniae were detected. The P1 adhesion gene of Mycoplasma pneumoniae and the 16S ribosome gene specific for Chlamydia pneumoniae were detected with polymerase chain reaction (PCR). Legionella antigen in urine was detected using enzyme immunoassay (EIA) method. Sputum samples were collected for culture, and bacteria were isolated and identified using conventional methods.
Results: The etiology of CAP was identified in 50 (48.5%) patients. The distribution of causal agents was as follows: Mycoplasma pneumoniae in 23 (22.3%) cases, Legionella pneumophilia 3 (2.9%), Chlamydia pneumoniae 2 (1.9%), streptococcus pneumoniae 12 (11.7%), Haemophilus influenzae 9 (8.7%), and Klebsiella pneumoniae 7(6.8%). In 6 patients (5.8%) more than one causal agent were found, among them Mycoplasma pneumoniae was found in 5 cases with mixed infections.
Conclusions: Atypical pathogens especially Mycoplasma pneumoniae have an important role in CAP. Streptococcus pneumoniae and Haemophilus influenzae remain the most common bacteria, and mixed infection should not be ignored.