How frequently do we need to repeat mass antibiotic distributions to eliminate trachoma in Ethiopia?

Abstract

Abstract: : Purpose: The WHO and their partners are attempting to eliminate blinding trachoma, in large part by the use of mass azithromycin administrations. While annual treatments have had success in areas with modest disease such as Morocco and Nepal, preliminary results in hyper–endemic regions have been less encouraging. Mathematical models have demonstrated that it is theoretically possible to eliminate infection with repeat mass treatments, given sufficient coverage of the population and given a slow enough return of infection back into the population after treatment (which can be expressed as an initial doubling time). This doubling time has not previously been calculated. Here we determine the doubling time of chlamydial infection returning into a hyper–endemic population in Ethiopia and estimate the treatment frequency (i.e. biannual, annual, etc.) required to eliminate infection. Methods: 40 villages in the Gurage Zone of Ethiopia were monitored for infection at baseline, 2 months after treatment, and 6 months after treatment, using the Amplicor PCR test on conjunctival swabs from all children aged 1–5 years. Doubling times were calculated based on 2 and 6 month data. Inter–village variance was estimated, and confidence intervals were used to express uncertainty due to sampling error. A sensitivity analysis was also performed. Results: 2714 individuals were monitored. Baseline prevalence of infection was 48% (95% CI 43–53%), 2 months post–treatment prevalence was 4.8% (3.0–6.6%) and 6 months post–treatment 12.0% (8.2%–15.8%). The prevalence of infection doubled every 3.0 months (2.0 to 6.4 months). The treatment frequency necessary for elimination was estimated as every 7.6 months (5.0 to 16.2 months). In estimating the necessary treatment frequency, uncertainty of the doubling time is far more important than uncertainty of the coverage level. Conclusions: Results in Ethiopia imply that biannual mass antibiotic administrations with attainable coverage levels may be sufficient to eventually eliminate infection. Annual distributions may not be enough. The necessary treatment frequency calculation is very sensitive to the estimation of the doubling time, and inter–village variance is sufficiently high that multiple villages need to be monitored to make a reasonable estimate of this parameter.

Keywords: trachoma • antibiotics/antifungals/antiparasitics • clinical (human) or epidemiologic studies: treatment/prevention assessment/controlled clinical trials