Chlamydia pneumoniae seroprevalence in immunocompetent and immunocompromised populations in Milan

Chlamydia pneumoniae is drawing increasing attention as an agent of respiratory tract infection. Specific antibody prevalence in western countries is low in preschool children and reaches more than 50% in adults. However, little is known about the prevalence of this infection in immunocompromised subjects such as HIV-I infected patients. The aim of this study was to evaluate the seroprevalence of Chl pneumoniae in immunocompetent and immunocompromised (HIV-1 infected) paediatric and adult populations.

Between March 1991 and September 1992 764 healthy subjects (421 men and 343 women, age range six months-81 years), 96 HIV-I infected (73 men and 23 women, age range 18-35 years) and 126 HIV-I negative intravenous drug users (92 men and 34 women, age range 18-37 years), and 50 children (23 boys and 27 girls, age range 8-123 months) with vertically transmitted HIV-I infection were studied. For each subject an HIV-I test (ELISA and Western blot) was performed, together with a microimmunofluorescence test for IgG and IgM antibodies to Chl pneumoniae specific antigen (TW-183).

In the healthy population a low prevalence (11%) was observed in children under 10 years of age, which increased progressively to 58% in adults over 70 years. In the HIV-I infected population Chl pneumoniae seroprevalence was higher than in immunocompetent controls (children, 26% v 11%; drug users, 60% v 40%). Moreover, in drug users this difference was also observed in comparison with HIV-1 negative intravenous drug users (60% v 33%).

Our data on Chl pneumoniae seroprevalence in a healthy population are consistent with those reported by others in western countries. Moreover, HIV-I infected subjects seem to be at higher risk of developing Chl pneumoniae infections.