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J.D. Chidambaram, M. Melese, W. Alemayehu, V. Cevallos, E. Yi, C. Donnellan, Z. Zhou, B.D. Gaynor, J.P. Whitcher, T.M. Lietman; Monitoring Trachoma Infection After Mass Antibiotic Treatment: The Long Lag Time of the Clinical Examination . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5019.
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Purpose: Trachoma remains the leading infectious cause of blindness worldwide. The WHO and its partners currently recommend mass antibiotic distribution as part of their program to control the ocular chlamydia that causes the disease. Clinical examination is the most widely used method to monitor efficacy of these treatments. However, there is some debate over its correlation with the presence of ocular chlamydial infection in an individual, particularly following antibiotic treatment. There has been little work on this correlation at the village level, because this requires monitoring multiple villages. Here we examine the relationship between prevalence of clinical activity and ocular chlamydial infection in Ethiopian villages before and after antibiotic treatment. Methods: 40 villages were randomly chosen from Gurage Zone, Ethiopia in Spring 2003. Before treatment, children were examined using the WHO simplified trachoma grading system to identify presence of active trachoma. Right upper conjunctival swabs were taken to determine the prevalence of ocular chlamydial infection. Swabs were tested for chlamydial DNA using Amplicor. All villagers aged ≥1 year were offered single dose oral azithromycin. Clinical exam and PCR testing was repeated at 2–, 6–, and 12– months post–treatment. Results: At baseline in 1–5 year olds, mean village PCR prevalence of infection was 48.9% and in 1–9 year olds prevalence of clinically active trachoma was 85.3% (n=2089). Two months post–treatment of 92% of the population, the prevalence of infection was 5.8% and clinical activity was 72.3% (n=2181). Pre–treatment PCR and clinical exam prevalence are well correlated (r=0.74, p<0.0001). Two months post–treatment, the correlation falls (r=0.35, p=0.31). A multivariate model indicates that the clinical exam at 12 months is the best predictor of infection at 2 months (p=0.03), followed by the clinical exam at 6 months (p=0.08) and then 2 months post–treatment (p=0.48), suggesting a long lag–time in the clinical exam. Conclusions: If the clinical exam is used to monitor ocular chlamydial infection, two things should be kept in mind: 1) The clinical exam may overestimate the level of infection in a community, and this discrepancy is most marked soon after treatment. 2) The prevalence of clinical activity does correlate with the level of infection after mass treatment, but there appears to be a lag time in the clinical exam of at least 10 months.
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