Screening

Well-designed clinical trials are needed to strengthen the evidence about the accuracy, effectiveness (including the impact on patient-important outcomes such as mortality), feasibility and cost implications of using the W4SS, CRP, CXR and mWRD to screen for TB across all HIV subpopulations in settings with low, medium and high burdens of HIV and TB with and without high ART coverage.

Well-designed trials and rigorous quasi-experimental studies in different settings are required to investigate the effects of population-wide systematic screening for TB on individual-level outcomes (diagnostic delay, treatment outcomes, costs to patients, social consequences) and populationlevel outcomes (TB prevalence, incidence, transmission), as well as to guide implementation choices (including the method of delivery, screening algorithms, the duration of screening intervals and frequency of screening, and the mode of delivering the intervention).

When CAD is implemented, local calibration is advised to customize the score thresholds to the requirements of the programme (see the operational handbook for more details about how this can be done) (7). After this initial calibration, ongoing monitoring and analysis of CAD performance should be carried out to assess the correlation with human readers’ interpretations and with bacteriological confirmation, and with the proportion of images read as abnormal and requiring further investigation.

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.

In this guideline, recommendations about systematic screening for TB disease are made for distinct populations for whom it is judged that the benefits and desirable effects of screening outweigh the potential harms.

In order to obtain the required information for the indicators described above, a TB recording and reporting system needs to include a minimal set of data elements. Although paper-based systems have been used to collect such data, it is now becoming increasingly feasible to collect data electronically, and this should be the standard aspired to for monitoring TB screening activities. The following strategies can be used to collect the necessary data:

Continued monitoring can help programme managers assess the performance of the TB screening components that are within their purview. The following indicators should be considered for each targeted risk group:

1. the number of people eligible for screening;

2. the number of people screened (considering the first screening and second screening separately, if applicable);

3. the proportion of those eligible for screening who were screened;

4. the number of people with presumptive TB who were identified;

Tuberculosis (TB) is a leading cause of death from a single infectious agent, despite being largely curable and preventable. In 2019, an estimated 2.9 million of the 10 million people who fell ill with TB were not diagnosed or reported to the World Health Organization (WHO) (1).