Which members of a community need antibiotics to control trachoma?: Conjunctival Chlamydia trachomatis infection load in Gambian villages

PURPOSE. Trachoma is the leading cause of infectious blindness worldwide. Control strategies target antibiotic therapy to individuals likely to be infected with Chlamydia trachomatis on the basis of clinical signs. However, many studies have found chlamydial infection in the absence of clinical disease. It has been unclear whether such individuals represent a significant reservoir of infection. In the current study, a quantitative polymerase chain reaction (PCR) assay was used to investigate the distribution and determinants of chlamydial infection load in an endemic community, and the findings were used to evaluate the potential effectiveness of different control strategies. METHODS. Members of a trachoma-endemic community (n = 1319) in a rural area of The Gambia were examined for signs of disease, and tarsal conjunctival swab samples were collected. C trachomatis was initially detected by qualitative PCR. The load of infection was then estimated by real-time quantitative PCR. RESULTS. Chlamydial infection was detected in 7.2% of the population. The distribution of infection load was skewed, with a few individuals having high loads. Only 24% of infected individuals had signs of active trachoma. Infection loads were higher in those with clinically active disease and were highest among those with severe inflammatory trachoma. High infection loads were associated with having no accessible latrine and living with a person with active disease. CONCLUSIONS. In this low-prevalence setting, infected individuals without signs of active trachoma constitute a significant reservoir of infection. Treatment of a defined unit of people who live with someone with clinically active trachoma would effectively target antibiotic treatment to infected people without signs of disease.