HomeClinical assessment, TB screening and follow-up should follow standard practices, and TB programs should have clearly identified clinical referral pathways for contacts (see Chapter 4: Diagnosis of Tuberculosis Infection and Chapter 9: Pediatric Tuberculosis). Participation rates for TB screening may be higher if it is done directly by TB program staff, whether at the home/exposure site, or at a TB clinic.
All identified contacts who have no symptoms of TB disease, and are not already known to have tested positive on a TST or an interferon-gamma release assay (IGRA), should be assessed for LTBI. The results should be interpreted regardless of Bacille Calmette-Guérin (BCG) vaccination status. Similarly, for people whose first-ever TST and/or IGRA is performed because of the contact investigation, a positive result could reflect infection in the past (remotely) rather than by the recent case. Nevertheless, because of the risk associated with recent exposure, for clinical and public health management, the positive result must be interpreted as a recent infection (see also Chapter 4: Diagnosis of Tuberculosis Infection). If a TST is the screening test for LTBI, high-priority contacts should ideally have both an initial TST immediately and a second TST at least 8 weeks from the last day of exposure, to identify conversion. If LTBI screening is done by IGRA, a single test at 8 weeks after exposure should be done.
In many medium-priority exposure settings, it is most practical to do a single round of screening after 8 weeks from the last exposure. Especially for non-household contacts, participation rates drop significantly between initial and post-8-week screenings as the level of initial anxiety declines, with up to 50% of those whose initial TST is negative lost to follow-up.54 Also, as more time elapses before the initial test, it is progressively less likely that conversions will be detectable since many infected contacts may have already converted to a positive TST. Thus, if an initial screening cannot be organized before 4 weeks from the last exposure and loss to follow-up minimized, it is generally more efficient to do a single post-8-week screening. In populations in which many people have prior exposure to TB or BCG vaccination (eg, immigrants from high-incidence countries), this also avoids false TST “conversion” related to boosting. In the rare situation that low-priority contacts are investigated, we suggest only a single test at least eight weeks from the last day of exposure.
A 2-step TST (two TSTs done a week apart) is not equivalent to an initial and post-8-week TST. Two-step TSTs are not appropriate in contact investigations (see Chapter 4: Diagnosis of Tuberculosis Infection).
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