Prevalence of Antibodies to Chlamydia pneumoniae(Strain TWAR) and other Chlamydia in Japan

Chlamydia pneumoniae (Strain TWAR), the new third species of genus Chlamydia, is emerging as an important human respiratory pathogen in Western countries. However, little is known about it in Japan. In this study, 1330 serum samples were tested for seroprevalence of three species of genus Chlamydia including C. pneumoniae in Hiroshima. Microimmunofluorescence test was used to measure serum IgG antibody, and formalinfixed elementary bodies of C. trachomatis, C. psittaci, and C. pneumoniae were used as antigen. Serum titer of 1: 32 or greater was considered positive. Seropositive rate of C. pneumoniae began to increase around the 6 month to 3 year old age group and reached 44% in the 8 to 11 year olds. A peak of seroprevalence according to age was around 20 year old, and about half of the adults were seropositive. Outpatients and healthy persons held almost the same seropositive rate. The positive rate in childhood was higher and the peak appeared earlier than some former studies in Western countries. The seropositive rate of C. trachomatis was noted 1-2% in the 6 month-7 year old age group, but no seropositive child was found in the 8-15 year olds. The rate was increased after adolescence and reached 10% in adults. The seroprevalence of C. psittaci was 1%. These data suggest C. pneumoniae is the most prevalent Chlamydia in Japan and as prevalent as in the Western countries.