ReacciónThe magnitude and balance of desirable and undesirable effects vary according the epidemiological conditions (the prevalence of TB and of risk factors) and the intensity of the screening intervention being implemented (the coverage of the population and the sensitivity of the screening test and algorithm). There is currently no evidence that population-wide screening using less sensitive screening algorithms that begin with symptom screening are effective at reducing the population prevalence or transmission of TB. However, there is limited evidence that screening utilizing symptom-based screening tools may benefit individuals who are diagnosed with TB by leading to earlier diagnosis with less severe TB disease, lower costs to the patient and lower risk of catastrophic costs associated with the course of disease. The balance of potential benefits and harms of screening may tip in favour of the intervention depending on factors such as the prevalence of TB in the population to be screened (particularly undetected TB), the accuracy of the screening and diagnostic tests used, the degree of current TB case detection and the vulnerability of the population being screened.
Screening should be conducted using the most sensitive and specific screening algorithm possible, with a screening test that identifies those with a higher likelihood of having TB and a diagnostic test to confirm the diagnosis. Highly accurate screening tests such as CXR and mWRDs have high sensitivity, specificity, or both; however, the feasibility of their use is affected by resource and implementation requirements. Symptom screening is less accurate (reduced sensitivity, specificity, or both), but is generally considered much more feasible to implement. Recent evidence suggests that reductions in the population prevalence of TB can be achieved with repeated annual screenings using a sensitive screening algorithm (mWRD followed by clinical evaluation) (13). See Section 3 for recommendations on tools for screening for more discussion on this topic.
While the implementation of a population-wide screening programme inevitably requires a significant investment of resources, overall there may be potential long-term savings to be made for health services through reduced future incidence. The costs of conducting community-wide screening will vary greatly, depending on the screening and diagnostic tests used and the population prevalence of TB. The cost–effectiveness of population-wide screening using a highly accurate algorithm is unknown, but the higher the prevalence, the more cost–effective the intervention will be. Using a highly accurate screening and diagnostic algorithm will inevitably require more resources than using symptom-based screening approaches, but it has a greater potential to reduce the population burden of TB.
The optimal frequency of screening in a general population to achieve individual- or community-level benefits remains unclear. There is also uncertainty about how people value the benefits expected from being screened. A review of qualitative studies of community perceptions of TB screening showed that, in general, screening was acceptable. However, resistance to screening was common, resulting from a combination of disparate factors, such as having a perception of being at low risk for TB among healthy participants, having little conviction in the effectiveness of screening, holding in poor regard TB services offered in the community, having concerns about confidentiality and the possible disclosure of diagnosis, and being anxious about the need to take TB medication.
Separate recommendations are made for select high-risk groups in the following sections. See the operational handbook for more details on the practicalities of implementing TB screening interventions using different tools and algorithms (7).