Why Chlamydia pneumoniae is associated with asthma and other chronic conditions? Suggestions from a survey in unselected 9 yr old schoolchildren

Despite numerous studies demonstrating an association between asthma and many other chronic conditions and signs of Chlamydia pneumoniae (Cp) infection, the role of Cp in the pathogenesis of these illness remain still unclear. We investigated the prevalence of Cp antigen in the upper airways and the prevalence of detectable Cp serum antibodies in an unselected population of 207 9‐yr‐old schoolchildren. We also sought the presence of asthma, chronic or recurrent respiratory symptoms by means of questionnaire completed by the parents. Nasal aspirate, blood sampling and allergen skin prick tests were also performed. None of the children had obvious signs of acute infection at physical examination. Cp DNA was detected in nasal aspirates from 20 of the 207 children tested and serum IgG antibodies for Cp in 68 children. No association was found between atopy or history of atopic illness and the presence of Cp DNA or antibody production. This finding is explained by the fact that our study was conducted in an unselected childhood population, inherently including few children with asthma. A strong association between the status of antigen carrier and the presence of detectable Cp serum immunoglobulin (Ig)G or IgM suggests that subjects with detectable Cp antibodies have an impaired ability to eliminate this pathogen when infected. Because Cp eradication requires a strong Th1 lymphocyte response, the previously proven association between Cp and asthma, might reflect the known association of asthma with Th2‐oriented lymphocytic activity.