Context Mass antibiotic administrations for ocular chlamydial infection play
a key role in the World Health Organization's trachoma control program. Mathematical
models suggest that it is possible to eliminate trachoma locally with repeat
mass treatment, depending on the coverage level of the population, frequency
of mass treatments, and rate that infection returns into a community after
each mass treatment. Precise estimates of this latter parameter have never
Objective To determine the rate at which chlamydial infection returns to a population
after mass treatment and to estimate the treatment frequency required for
elimination of ocular chlamydia from a community.
Design, Setting, and Participants Longitudinal cohort study of 24 randomly selected villages from the
Gurage Zone in Ethiopia conducted February 2003 to October 2003. A total of
1332 children aged 1 to 5 years were monitored for prevalence of ocular chlamydial
infection pretreatment and 2 and 6 months posttreatment.
Interventions All individuals older than 1 year were eligible for single-dose oral
azithromycin treatment. Pregnant women were offered tetracycline eye ointment.
Main Outcome Measures Prevalence of ocular chlamydial infection, measured by polymerase chain
reaction, in children aged 1 to 5 years, in each of 24 villages at each time
point was used to estimate the rate of return of infection and the treatment
frequency necessary for elimination.
Results The prevalence of infection was 56.3% pretreatment (95% confidence interval
[CI], 47.5%-65.1%), 6.7% 2 months posttreatment (95% CI, 4.2%-9.2%), and 11.0%
6 months posttreatment (95% CI, 7.3%-14.7%). Infection returned after treatment
at an exponential rate of 12.3% per month (95% CI, 4.6%-19.9% per month).
The minimum treatment frequency necessary for elimination was calculated to
be once every 11.6 months (95% CI, 7.2-30.9 months), given a coverage level
of 80%. Thus, biannual treatment, already being performed in some areas, was
estimated to be more than frequent enough to eventually eliminate infection.
Conclusion The rate at which ocular chlamydial infection returns to a community
after mass treatment suggests that elimination of infection in a hyperendemic
area is feasible with biannual mass antibiotic administrations and attainable