Chlamydia pneumoniae in community-acquired pneumonia.

Chlamydia pneumoniae has been established recently as an important human respiratory pathogen. The aim of this study was to define the prevalence of C. pneumoniae in community-acquired pneumonia. We prospectively investigated adult patients who were treated as inpatients and outpatients. Acute and convalescent serum samples were obtained from each patient. Serological diagnosis of C. pneumoniae infection was determined by enzyme-linked immunosorbent assay (ELISA). Eighty paired sera were tested for C. pneumoniae-specific IgM, IgG and IgA. Twenty-one patients (26.2%) had serological results compatible with acute C. pneumoniae infection. Eighteen (85.7%) of these infected patients were C. pneumoniae-specific IgM positive, three had a seroconversion of IgA and two had a four-fold or greater increase in C. pneumoniae-specific IgG antibody titer. The most common clinical manifestations of community-acquired pneumonia due to C. pneumoniae were fever (100%), cough (100%), chest pain (47.6%) and shortness of breath (42.9%). Physical examination revealed crackle in 85.7 per cent of the cases. These findings suggest that C. pneumoniae is a common cause of community-acquired pneumonia in Thailand.