Serological evidence for Chlamydia pneumoniae infection following diphtheria-tetanus-pertussis booster vaccination

Increased mortality and morbidity with intracellular pathogens has been reported in females with diphtheria-tetanus-pertussis (DTP) as their most recent vaccination. Within a randomised trial, we investigated the effect of DTP on Chlamydia pneumoniaeserology. Eighteen-month-old children were randomised to DTP booster and oral polio vaccine (OPV) or OPV only. Blood samples collected from 523 children at baseline and six months later were analysed for C. pneumoniae antibodies. The C. pneumoniae IgG seroprevalence was high, with 12% positive at 18 months of age. Loss of IgG positivity was common during follow-up (25/65 (38%)), and was associated with lower weight-for-age. DTP did not affect the incidence of IgG seroconversion or IgM positivity. Among normal-weight children, DTP vaccination was associated with an increase in C. pneumoniae infection for females, whereas the trend was the opposite among males (p = 0.05, test of interaction between sex and DTP). Among DTP-vaccinated children, the male-female risk ratio was 2.23 (95% CI = 0.88 - 5.66) for IgG seroconversion and 0.0 (95% CI = 0.0 - 0.77) for IgM positivity. The overall C. pneumoniae seroprevalence in young children was high even though loss of IgG positivity was common. We found sex differences in IgG seroconversion and in IgM positivity among DTP-vaccinated children.   Key words: Chlamydia pneumoniae, diphtheria-tetanus-pertussis, serology, child, low-income countries, prevalence, non-specific effects, vaccinations.