Prevalence of antibody to Chlamydia in renal transplant recipients and other population groups.

The serologic response to Chlamydia was determined with three sequential serum specimens from 25 renal transplant recipients (RTR) and from 25 blood donors who were matched for age and sex with the study group. Antibodies to Chlamydia were also measured in serum specimens from several other populations. The geometric mean titers (GMT) were significantly higher (P less than 0.05) for infants with pneumonia (1:6927) and women attending a sexually transmitted disease (STD) clinic (1:35) compared with pregnant women (1:25), normal infants, less than 23 weeks of age (1:11), and RTR (1:13). Titer increases of greater than or equal to fourfold were detected in 4 of 25 (16%) RTR, but could not be correlated with clinical pneumonia. Because of the high background prevalence (20% in RTR, 80% in STD patients), combined with low GMT of chlamydial antibody in these groups, the serologic diagnosis of respiratory tract infections in immunosuppressed adults required serial serum specimens.