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A.T. Broman, K. Shum, B. Munoz, D. Duncan, A. Foster, D.C. W. Mabey, S.K. West; Spatial Clustering of Ocular Chlamydial Infection Over Time Following Mass Treatment, Among Households in Maindi, Tanzania . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5016.
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Purpose: To determine if there exists spatial clustering of households occupied by children with high levels of ocular chlamydial infection, over time, following treatment. Methods: The population of Maindi consists of 1029 residents, and all were invited to participate in the study. Right eyes were examined for signs of trachoma, and a swab of the conjunctiva was taken with attention paid to avoid contamination. A global positioning system unit recorded the location of each house. Mass treatment with Azithromycin was offered, with participation above 80%. Active trachoma was assessed and swab samples were taken at 2, 6, 12, and 18 months after mass treatment. Swabs were analyzed using the Amplicor qualitative PCR assay, testing for presence or absence of C. trachomatis; in swabs that tested positive, an additional quantitative test was used to determine number of infectious particles per swab. This analysis focuses on households with children younger than 8 years, since pre–school children are the main reservoir of infection. Household load of chlamydia infection in children was averaged, and a k–function analysis was performed to detect clustering of households with average infection higher than the median household loading at baseline. Results: A total of 873 Maindi villagers participated in this study at baseline; of these, 271 (31.0 %) were children younger than 8 years. The total number of households participating was 215, with 182 (84.6 %) households having at least one child; of these, 112 (61.2 %) households had at least one infected child. Among households with infected children, average household loading of infection in children had a median of 32.4 copies/swab at baseline (IQR=[5.7, 1336.2]). K–function analysis showed clustering of high–infection households at distances up to a mile at baseline; at two months following treatment clustering was not significant; and at six months slight clustering existed within 0.3 miles. At 12 and 18 months there was significant clustering of high–infection households, for distances less than 0.7 miles. Conclusions: Households with high loading of ocular chlamydia appeared to cluster at distances less than a mile. Although mass treatment effectively eliminates this clustering in the short term, at 6 to 12 months we detect clustering of high infection households at almost the same distance found in the community prior to treatment.
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