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J.D. Chidambaram, M. Melese, W. Alemayehu, V. Cevallos, C. Donnellan, Z.X. Zhou, E.H. Yi, J.P. Whitcher, B.D. Gaynor, T.M. Lietman; Do untreated children receive an indirect, protective effect following mass antibiotic treatment for trachoma? . Invest. Ophthalmol. Vis. Sci. 2004;45(13):3744.
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Purpose: The WHO and its partners have initiated a program to eliminate blinding trachoma by the year 2020. A major strategy of this program is the mass distribution of antibiotics targeting the ocular Chlamydia that cause trachoma. In practice it is not possible to treat everyone in a population. However, mathematical models imply that untreated individuals receive an indirect, protective effect by residing in a community where most others have been treated, as those left untreated will then be less likely to be infected. Here we compare the prevalence of infection in untreated children residing in treated versus untreated villages to estimate this indirect, protective effect. Methods: 8 villages were randomly chosen from a district of Gurage Zone, Ethiopia. In Spring 2003, all individuals ≥1 year of age in these villages were offered single–dose oral azithromycin. Children <1 year of age were not treated as azithromycin is not approved in this age group. In Fall 2003, 8 additional villages were randomly chosen, and monitored prior to their future antibiotic treatments. Right upper conjunctival swabs were obtained from all children ≤18 months in all 16 villages in the Fall (children in this age group had not received treatment 6 months earlier, whether or not they resided in a treated village). All samples were assayed for chlamydial DNA using the Amplicor test. Results were analyzed with a logistic regression model, accounting for clustering within villages. Results: In Gurage Zone, prevalence of chlamydial infection in children aged 1–5 years was 48% (95% CI 43–53%) pre–treatment. In treated villages, 87% of individuals ≥1 year of age received azithromycin. Six months later, the chlamydial infection rate was 3.8% in untreated younger children (≤18 months) in treated villages (N=132). Concurrently, the infection rate was 10.3% among this age group in untreated villages (N=87). There was a significant 2.9–fold increased risk of chlamydial infection in untreated villages (P=0.025). Conclusions: Children not treated for trachoma apparently receive some protection from infection by residing in a treated village. This indirect effect of repeat mass antibiotic distributions may be analogous to the herd immunity provided by vaccination programs with incomplete coverage, supporting the concept that repeat mass antibiotic administrations can theoretically eradicate infection locally, even without complete coverage.
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