To avoid barriers or delays created by TB infection testing, and to minimize associated losses in the TB infection care cascade, an integrated person-centred care model is preferred for TB infection diagnosis and treatment. Here, “integrated” means carrying out screening for TB disease and testing for TB infection in parallel, and “person-centred care” means coordination of multiple care activities during the same visits. This care model could shorten delays to appropriate treatment initiation, minimize time and cost burden on patients and their families, and promote retention in the TB infection cascade of care. Family-centred care is an extension of person-centred care, with care for the entire family coordinated to minimize time and cost burden on the entire family. This approach is particularly useful for contact investigation in households, is conducive to greater yield and retention on treatment, and is more cost-effective (8).
In many settings, access to TB infection testing is currently suboptimal. Thus, making testing obligatory before starting TPT would create a barrier for many individuals who would benefit from such treatment and hence create a barrier for global expansion of TPT. To ensure TPT for individuals at particularly high risk of TB disease (e.g. child contacts aged below 5 years and People with HIV), current WHO guidance strongly recommends TPT even without TB infection testing.
An integrated algorithm for TPT among contacts (aged <5 years), People with HIV and other risk groups has been released by WHO as Module 1 of the guidelines (1). For household contacts who are aged 5 years and older, and who are not HIV-positive, TB infection testing is advised as part of their care. Given that contacts are also at risk of TB disease, an integration of TB infection testing with TB screening would be an important step to enhance implementation.
In the first visit, as soon as someone at high risk of TB is identified, that person should undergo TB screening and at the same time should be tested for TB infection (Fig. 2.1). TB screening could be performed, for example, by assessing TB symptoms or using more sensitive WHO-recommended tools such as CXR, with or without computer-aided detection, molecular WHO-recommended rapid diagnostics or C-reactive protein (for People with HIV) (28). Sequential screening and diagnostic testing (first for TB disease, then for TB infection) may incur substantial delays or losses in TB infection testing, particularly if these tasks are performed by different health care personnel or in different locations. Hence, during the first health care encounter, it is preferable to combine screening for TB disease with testing for TB infection. People with symptoms that are suggestive of TB disease should undergo further evaluation as soon as possible, preferably on the same visit (29).
The second visit may be optimized for reading the TB skin test or obtaining the IGRA result; reviewing the results of microbiological tests for TB disease if the person had a positive TB screen and submitted samples for TB testing; undertaking clinical evaluation to rule out TB or before starting TB treatment; and starting TPT or TB treatment. This second visit should occur 48–72 hours after the test. If the TB infection test is negative, the individual can be discharged although aa repeat TB infection test may be required if an initial test is negative – particularly in those with very recent exposure or concomitant viral infection. When the TB infection test is positive in contacts who were asymptomatic initially, or who had symptoms but in whom TB disease was excluded, should be re-evaluated for immediate initiation of TPT (Fig. 2.1). Although TB infection tests may be positive in the presence of TB disease, their low accuracy means that these tests are not recommended for screening or as part of the diagnostic work-up of presumptive TB and this should be emphasized during the training of health care workers.
It is proposed to conduct TB infection testing early in the assessment of people at risk of TB (i.e. during the first visit) which helps to reduce delays in starting the appropriate treatment, and the test result may be helpful when deciding the best course of action in most of the people tested. If the person had no symptoms at screening, evaluation to exclude TB disease may still be warranted and CXR increases the sensitivity in such situations. Ideally, all these activities should be done on the same day, so that TPT can be prescribed during the second visit as soon as test results are available. Because most people with TB symptoms are not expected to have TB disease, deferring TB infection testing to a later stage (e.g. after further work-up) in such individuals may result in significant losses.
Fig. 2.1. Algorithm for person-centred TB infection care; integrated infection and disease assessment where TB infection testing is availablea and recommended.
CXR: chest X-ray; IGRA: interferon-gamma release assay; People with HIV: people living with human immunodeficiency virus; TB: tuberculosis;
TBI: TB infection; TBST: Mycobacterium tuberculosis antigen-based skin test; TPT: TB preventive treatment; TST: tuberculin skin test; WHO: World Health Organization.
ᵃ Where testing is not available (or not required based on local circumstances), the algorithm in the WHO operational handbook (30) can be used
ᵇ TB screening performed using four TB symptoms (cough, fever, night sweats and weight loss). The WHO-recommended screening tools with high accuracy are preferred; they include CXR (with or without computer-aided detection), WHO-recommended rapid diagnostics or C-reactive protein (for People with HIV) (28).
ᶜ TB infection tests include TST, IGRAs and TBSTs.
ᵈ A thorough clinical assessment should be performed to exclude TB disease (including extrapulmonary TB) and should include CXR where available. A WHO-recommended rapid diagnostic test should be used for diagnosis of TB disease where available (31).
ᵉ Individuals screened using only symptoms initially should be carefully assessed for TB disease (including for extrapulmonary TB); the screening should include CXR where available, to rule out TB disease before initiating TPT.
ᶠ In circumstances where a test may be suspected to be false negative (e.g. concurrent viral infection), repeat testing may be considered after 30 days.
g Details on eligibility criteria and regimen choices can be found in the relevant WHO guidelines (1).
The programmatic decision to initiate TB infection testing implies a commitment to start TPT rapidly where indicated. Hence, the programme should ensure that the referral pathways and medical services are well organized before launching testing for TB infection, and that the mechanisms for clinical assessment, start of medication and treatment support are all available (Chapter 4). An advantage of skin testing for TB infection (using TST or TBST) is the capacity to administer the test and read the result at the point of care. The portable nature of the supplies and materials needed for the test mean that testing can be done at home or in remote communities. However, these advantages are lost if the subsequent evaluation to exclude TB disease and the provision of TPT are not equally accessible. Hence, a decision to expand access to testing for TB infection needs to be matched by efforts to expand access to the medical services needed for management of those with positive test results.