4.3 Programmatic evaluations

A successful screening programme may lead to a diminishing yield, at least if the risk group is a fixed population. Over time, changes in the background burden of TB, as well as changes in the profile of TB patients in the community (e.g. a trend towards fewer patients with symptomatic TB) can lead to a reduction in the yield from screening, an increase in the NNS, a reduction in cost–effectiveness and a change in the ratio of benefits to harms. Trends in all of these indicators need to be monitored, and the prioritization of risk groups, choice of screening approach and screening interval should be regularly reassessed. Criteria for stopping screening should be established before a screening initiative is implemented.

Monitoring the indicators discussed above may point to the need for a special assessment, for example, to explore the reasons for a low uptake of screening, an unexpectedly low proportion of people with presumptive TB that was identified through screening, a low proportion of those with presumptive TB undergoing a diagnostic investigation and a higher than expected NNS. Additional quantitative and qualitative analyses may be needed to determine whether there are barriers to screening and to identify opportunities to improve the screening approach.

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