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J. D. Keenan, T. Lakew, W. Alemayehu, M. Melese, J. House, K. Hong, Z. Zhou, T. C. Porco, B. D. Gaynor, T. M. Lietman; The Importance of Coverage in Mass Antibiotic Distributions for Trachoma. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2405.
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The World Health Organization recommends repeated annual mass antibiotic distributions to control the ocular strains of chlamydia that cause trachoma. It is thought that the proportion of individuals in a village receiving treatment (i.e., antibiotic coverage) is an important predictor for the reduction of ocular chlamydia, though this has not been shown empirically. Here, we evaluate whether antibiotic coverage predicts chlamydial prevalence at 2 months and 6 months post-treatment.
As part of a clinical trial assessing the efficacy of mass antibiotic treatments for ocular chlamydia, all persons in 40 villages in the Gurage zone of Ethiopia were offered mass oral azithromycin at baseline. Antibiotic coverage was defined as the proportion of individuals from the baseline census who accepted a directly observed, single dose of oral azithromycin. Conjunctival swabbing was performed at baseline (pre-treatment), 2 months, and 6 months on all children ages 1-5; swabs were assayed for chlamydial DNA using Amplicor PCR. Multiple linear regression was conducted, using chlamydial infection at 2 months or 6 months as the response variable, and baseline infection, infection at 2 months, and antibiotic coverage as the explanatory variables. All prevalence figures were square-root transformed to optimize residual homoskedasticity and normality in regression analyses.
Mean baseline chlamydial infection in 1-5 year olds was 48.9% (95% confidence interval [CI] 42.8 to 55.0%), which was reduced to 5.4% (95% CI 3.9 to 7.0%) by 2 months post-treatment (p<0.01), and then rose to 7.9% (95% CI 5.4 to 10.4%) by six months post-treatment (p=0.03, compared to 2 months). Antibiotic coverage ranged from 73.9 to 100%, with a mean of 90.6% (95% CI 88.7 to 92.4%). Chlamydial infection at 2 months was predicted by baseline chlamydial infection (p<0.01) and antibiotic coverage (p<0.01), R2=0.53. Chlamydial infection at 6 months was predicted by baseline infection (p<0.01), but not by antibiotic coverage (p=0.29), R2=0.35.
Antibiotic coverage is an important short-term predictor of chlamydial infection, but does not appear to be a strong predictor of infection after many months have passed. A wider range of antibiotic coverage than found in this study might allow the assessment of a more subtle association.
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