Close contact investigation of TB in high-burden, low- and middle-income countries.

Tuberculosis (TB) remains a very common disease in most of the low- and middle-income countries. As a result of high disease burden, TB control measures in these countries are usually concentrated on intensifying active disease case-finding and early treatment of infectious TB. On the contrary, in countries with low disease burden, the focus is on contact investigation to identify latently infected individuals and prophylactically treating them to prevent disease reactivation and transmission. These two strategies are deemed important for the effective TB control. Nonetheless, WHO cautions that targeted contact investigation and latent TB infection (LTBI) treatment should only be undertaken by countries that have the operational capacity/ resources and have achieved ≥ 85% treatment success rate of active TB. The screening of LTBI is further challenged by the lack of a "gold standard" test to identify and validate individuals with this condition. Tuberculin skin test (TST) is still the preferred investigation as it is cheap, widely available and validated in many trials. The sensitivity and specificity of the newer test-interferon gamma release assay (IGRA) for LTBI screening has been encouraging in low prevalence countries. However, the evidence supporting such usage remains uncertain in high burden settings. Diagnosis of LTBI should adhere to the strict criteria outlined in the guidelines to avoid misdiagnosing active TB as LTBI. The treatment of the latter involved only one or two anti-TB drugs. It has been demonstrated that in the properly conducted contact screening and LTBI treatment, chances of the emergence of multi-drug-resistant TB is very low.