High prevalence of antibodies to Chlamydia pneumoniae; determinants of IgG and IgA seropositivity among Jerusalem residents.

The prevalence of antibodies to Chlamydia pneumoniae was examined in a stratified random sample of 581 Jerusalem adult residents between August 1987 and March 1989. IgG and IgA titres were measured by microimmunofluorescence, and associations with smoking and socio-demographic variables were assessed. IgG antibodies were found in 84.5% (95% confidence interval (CI): 80.4-87.9) of men and 68.7% (95% CI: 61.6-75.0) of women (P < 0.0001 for sex difference), indicating a very high rate of exposure in this population. IgA antibodies, postulated to represent persistent infection, were present in 45.1% (95% CI: 40.1-50.2) of men and 23% (95% CI: 17.4-29.7) of women (P < 0.0001 for sex difference). Factors associated with IgG seropositivity included family size, education and social class. On the other hand age (in men) and smoking were associated with IgA seropositivity. These findings support the hypothesis that low socioeconomic status and household crowding may be predictive of exposure to or infection with this organism (IgG seropositivity), whereas they do not explain persistence of the infection putatively expressed as IgA seropositivity.