Does clinical diagnosis indicate ocular chlamydial infection in areas with a low prevalence of trachoma?

The WHO has initiated a global program to eliminate trachoma. This program includes mass antibiotic administrations to reduce the prevalence of Chlamydia trachomatis, the causative agent in trachoma. DNA amplification tests are the most sensitive methods to diagnose C. trachomatis infection, but are expensive and not typically performed in trachoma-endemic areas. Trachoma programs use clinical examination to determine which communities and which individuals within communities would benefit from antibiotic treatment, so understanding the relationship between clinical activity and chlamydial infection is important. In this study, we determine what percent of individuals with clinically active trachoma are infected with chlamydia in low prevalence communities of China and Nepal (with <10% clinical activity in children), and compare this against a high prevalence community of Nepal (with >30% clinical activity in children). In the low prevalence areas, only 8% clinically active cases had evidence of chlamydia. In the high prevalence community, 70% of clinically active cases harbored chlamydia. These results imply that clinical activity is less indicative of infection at a lower prevalence. In the context of a trachoma program, both clinically active cases and the community as a whole may stand to benefit less from antibiotic treatment in lower prevalence areas.