Clinical aspects of Chlamydia pneumoniae infection

This recently recognised member of the genus Chlamydia is one of the most widespread pathogens of man, though up to 90% of infected people have few or no symptoms. Several studies have estimated the population prevalence of antibodies to C. pneumoniae at 40-55% in the northern hemisphere, and over 60% in under-developed countries. The incidence of infections follows a cyclical pattern, with peaks at regular intervals of 2-10 years, but no apparent seasonal periodicity. Nosocomial transmission may be mediated by environmental surfaces as well as aerosols, and immunosuppression, for example by the human immunodeficiency virus, predisposes to infection. Chlamydia pneumoniae causes predominantly atypical pneumonia, often severe in adults, especially the elderly; including 5-10% of community-acquired pneumonia in Scandinavian countries. Serological evidence indicates associations with asthma, bronchitis, exacerbations of chronic airflow obstruction, otitis media and bronchiolitis. Several studies, using both serological and morbid anatomical techniques, also indicate associations with vascular atheroma and ischaemic heart disease, and with acute myocardial infarction. Chronic, latent and recurrent infections have been documented, and it is postulated that, like chronic or recurrent C. trachomatis infections, these may produce disease as a consequence of the host's immunological hypersensitivity. Several techniques are available for serological diagnosis: the technique of choice is micro-immunofluorescence, using fixed whole elementary or reticulate bodies as antigen, but antibody responses are highly variable. Traditional alternatives, antigen detection (by direct immunofluorescence or enzyme immunoassay) and cell culture, have major disadvantages. Polymerase chain reactions have not yet been widely applied to the clinical setting. tetracycline antibiotics, erythromycin and quinolones are not very efficacious in the treatment of C. pneumoniae infection. The azalide antibiotic, azithromycin, and the macrolide, clarithromycin, are active in vitro against C. pneumoniae, and may become treatments of choice. The development of anti-chlamydial vaccines remains an important research goal.