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ASTRA is a modification of lot quality assurance sampling (LQAS) billed as a cost-effective means of classifying communities as having low or high prevalence of active trachoma. Although this can be a reliable and cost effective means of community stratification for decision-making purposes, it may not provide sufficiently precise estimates of prevalence to be useful for securing a donation of azithromycin, or for determining the impact of interventions at follow-up |
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a non-overlapping subpopulation (often census enumeration areas) used as the sampling unit for trachoma prevalence surveys within a district |
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A commonly used method of selecting clusters for inclusion in population-based surveys of trachoma prevalence estimation at the district level. Clusters are randomly selected from a list of all the clusters within a defined area (e.g. a district). |
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| CO | Corneal Opacity |
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community |
A defined group of households, a village, or a group of neighboring villages, for which mass trachoma control activities can be implemented. A community may be as large as a sub district or may be smaller than a village |
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the usual administrative unit for health services |
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present in a population or area at all times (said of a disease or infectious agent) |
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a sensitive nucleic acid amplification technique to detect the presence of DNA from C trachomatis |
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population based prevalence survey (PBPS)
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considered the “gold standard” for estimating the prevalence of trachoma, PBPS typically use a two stage sampling process: 1) selection of clusters within a district (using cluster random sampling or probability proportionate to size sampling) 2)selection of households within clusters (e.g. through random selection). Children in selected households are examined for clinical signs of trachoma and adults may be examined for TT. The number of people to include in the survey (the sample size) is determined before the survey using standard sample size calculations |
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the proportion of individuals diagnosed with a specific disease or infection in a population at a particular time |
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administrative unit one level higher than the district |
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Surgery, Antibiotics, Facial cleanliness, Environmental improvement |
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Trachomatous inflammation - Follicular |
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TI |
Trachomatous inflammation - Intense |
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an operational tool that employs a convenience sample to identify high-risk communities and rank them to facilitate prioritization of control in worst affected areas. TRA cannot provide estimates of prevalence. WHO Guidelines for Rapid Assessment for Blinding Trachoma available here |
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Trachomatous Scarring |
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Trachomatous Trichiasis |