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J.D. Chidambaram, W. Alemayehu, M. Melese, K. Maxey, E. Yi, J. House, V. Cevallos, J.P. Whitcher, B.D. Gaynor, T.M. Lietman; Is There A Herd Protective Effect Associated With Annual Mass Antibiotic Distributions For Trachoma? . Invest. Ophthalmol. Vis. Sci. 2006;47(13):290.
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To control the ocular chlamydia that causes trachoma, a major cause of blindness worldwide, the WHO recommends annual mass antibiotic distribution with ≥80% coverage of the community. Achieving perfect coverage is difficult. Trachoma programs often are unable to treat children aged <1 year, for drug approval reasons. Many believe this age group may harbor a high prevalence of ocular chlamydial infection. Previously, we found that up to 6 months after mass treatment with >80% coverage, there may be an indirect protective effect for untreated babies aged <1 year. Here we evaluate whether this indirect effect lasts for 1 year, by comparing the prevalence of infection in untreated children, 1 year after high coverage mass treatment of their community, versus untreated children in villages which have not been treated.
In March 2003, 8 villages were randomly chosen from Gurage Zone, Ethiopia. All village residents aged ≥1 year were offered single dose azithromycin. Children aged <1 year remained untreated as azithromycin was not yet approved in this age group. In March 2004, 15 villages that had not yet been offered antibiotic were randomly chosen from the same original pool of villages. All children aged <2 years in all 23 villages were assessed for ocular chlamydial infection; right upper conjunctival swabs were obtained and assayed with the Amplicor PCR test to detect chlamydial DNA. In our larger study, 1–5 year olds in all 23 villages were monitored for ocular chlamydial infection. A logistic regression model used study arm, no. of children, and baseline prevalence of infection in 1–5 year olds as covariates.
Pre–treatment, the mean prevalence of infection in 1–5 year olds was 43.5% (n=516), and in <1 year olds was 3.8% (n=132). Mean antibiotic coverage was 91.3%. In March 2004, the mean prevalence of infection fell to 4.8% in untreated <2 year olds residing in treated villages (n=160). In the 15 newly enrolled villages, the mean prevalence of infection in <2 year olds was 8.6% (n=216), and in 1–5 year olds was 17.6% (n=805). The logistic model showed a significant protective effect for untreated babies residing in a treated village (OR 0.018, p<0.03).
There may be an indirect protective effect lasting up to 1 year for untreated individuals residing in a high–coverage village. The WHO recommends annually repeated mass treatments, and although high coverage remains important, perfect coverage may not be essential to eliminate infection from a community.
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