Abstract

Chlamydia pneumoniae TWAR is a newly recognized Chlamydia species that is a pathogen of respiratory tract infection. To clarify the endemic status of C. pneumoniae in Japan, we evaluated the incidence of C. pneumoniae antibody in 1,330 serum samples (660 from outpatients, 600 from normal individuals, and 70 from cord blood). The antibody titer was determined by a microimmunofluorescence test by using the elementary body of C. pneumoniae TW-183 as the antigen. Immunoglobulin G antibody titers of 1:32 or higher were regarded as evidence of past infection. The detection rate of C. pneumoniae antibody rapidly increased in subjects between the ages of 4 and 7 years, reached 44% in subjects between the ages of 8 and 11 years, and was about 50% in older subjects. The rate did not differ between healthy subjects and outpatients. These results suggest that C. pneumoniae infection is highly endemic in Japan as it is in Western countries. However, the antibody prevalence was high in the low age groups in Japan compared with that in Western countries.