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Approaches to screening will depend on each group, and intervention-specific indicators should be developed for each approach. In general, however, the data on indicators shown in Fig. 2.5 should be collected for each targeted risk group, such as all close contacts of TB patients or all people living with HIV in care.
Fig. 2.5 Data to be collected for systematic screening programmes for TB
The choice of screening programme will have implications for the resources required and the potential reach and effectiveness of the programme. The decision on which model to use should be based on determining which approach will be most effective for reaching the targeted risk group with the resources available. The effort and resources required to reach the target population can be limited by screening in locations where people gather for other purposes, such as health centres or workplaces, although not all populations can be reached in this way.
The NNS to identify one person with confirmed TB in a specific risk group is the inverse of the prevalence of detectable TB in that risk group, assuming 100% sensitivity of the screening and diagnostic tools being used.
Fig. 3 shows the potential yield of screening in a range of hypothetical risk groups with a range of relative risks of TB (assuming 100% coverage, acceptance of screening, sensitivity and specificity of screening). As illustrated in Fig. 2.2, the yield of TB screening in a specific risk group (in terms of the number of TB cases detected; y axis) depends on both the size of the risk group (i.e. the prevalence of the risk factor in the general population; x axis) and the relative risk of TB for that risk group (z axis).
Risk groups include groups at high risk of exposure to TB or of progression to TB disease or who have limited access to TB services. The following risk groups should always be systematically screened for TB:
The main purpose of an epidemiological assessment is to identify gaps in TB case detection and opportunities for addressing those gaps through screening. The assessment should account for potential benefits, risks and costs of systematic screening, particularly in relation to other possible interventions. The analysis should be disaggregated by age, sex and geographical location, and special attention should be paid to vulnerable groups that are at high risk for exposure and/or progression to TB disease or are likely to face barriers to accessing TB services, or both.
The cost of screening, especially as an outreach activity, can be high. The opportunity cost must be considered and compared with other means for improving early TB detection, such as improving the patient-initiated pathway to TB diagnosis (see 2.1.1). The efficiency of a screening programme can be increased by collaboration with other health and social programmes.
The two complementary approaches for improving early detection of TB are illustrated in Fig. 2.1 The primary approach is to optimize the patient-initiated pathway to TB diagnosis and treatment (for details see 2.1.1). This approach does not constitute screening and is a passive form of case detection.
Tuberculosis (TB) is a major yet preventable airborne infectious disease. About one fourth of the world’s population is infected with TB bacilli, the vast majority of whom have no disease (1, 2). In 2019, an estimated 10 million new TB cases emerged worldwide, and more than 1.4 million people died of TB, making it the leading single infectious disease cause of death that year (2). Of the estimated 10 million people who fell ill with TB in 2019, TB was not diagnosed in an estimated 2.9 million, and they were not enrolled in quality-assured TB treatment (2).