2.4.3 Potential impact on prevalence and transmission

The potential of screening to affect transmission is theoretically highest in congregate settings, such as prisons or overcrowded urban slums, where there is a high rate of transmission and where there is also substantial in-migration and out-migration. In a study in Viet Nam, 3 years of community-wide screening decreased the prevalence of pulmonary TB (26). In principle, the larger the total yield of screening, the larger the potential impact on TB transmission in the community. However, when the TB burden is concentrated in a few high-risk groups, the largest impact on overall transmission will be generated by screening carefully selected groups, even if the overall impact may be relatively small.

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