Diversity of Chlamydia trachomatis in Trachoma-Hyperendemic Communities Treated With Azithromycin

Abstract

Prior studies have theorized that low chlamydial genetic diversity following mass azithromycin treatments for trachoma may create a population bottleneck that prevents the return of infection, but little empirical evidence exists to support this hypothesis. In this study, a single mass azithromycin distribution was administered to 21 communities in the Gurage Zone of Ethiopia in 2003. All children aged 1-5 years had conjunctival swabs performed before treatment and 2 and 6 months after treatment. All swabs positive for Chlamydia trachomatis at 2 months underwent typing of the gene encoding the major outer membrane protein (ompA) of C. trachomatis, as did the same number of swabs per community from the pretreatment and 6-month visits. Diversity of ompA types, expressed as the reciprocal of Simpson's index, was calculated for each community. In total, 15 ompA types belonging to the A and B genovars were identified. The mean diversity was 2.11 (95% confidence interval: 1.79, 2.43) before treatment and 2.16 (95% confidence interval: 1.76, 2.55) 2 months after treatment (P = 0.78, paired t test). Diversity of ompA was not associated with the prevalence of ocular chlamydia (P = 0.76) and did not predict subsequent changes in the prevalence of ocular chlamydia (P = 0.32). This study found no evidence to support the theory that ompA diversity is associated with transmission of ocular chlamydia.

Figure 1.

Community diversity of genotypes for the gene encoding the major outer membrane protein (ompA) of Chlamydia trachomatis was not associated with the prevalence of ocular chlamydia in the Gurage Zone of Ethiopia in 2003. Each point represents a community in the Gurage Zone of Ethiopia. A) Cross-sectional relationship between diversity and prevalence of ocular chlamydia infection at 3 different time points: before mass azithromycin treatment (black), 2 months after the mass treatment (white), and 6 months after the mass treatment (gray). B) Relationship between posttreatment diversity and the prevalence of ocular chlamydia 4 months later. Diversity is expressed as 1 ÷ Simpson’s index, and prevalence was assessed in a random sample of children aged 1–5 years in each community.