Identification of latent TB infection key to curb spread of the disease

As the incidence of tuberculosis (TB) in the Nordic countries is low, the knowledge of the disease in this region of the world amongst professionals as well as in the general public decreases. Nevertheless, latent TB poses a serious health threat that requires adequate management.

Prof. Tuula Vasankari (University of Turku, Finland) gave an update on latent TB, which can be classified as a persistent immune response to stimulation by M. tuberculosis antigens with no evidence of clinically active TB disease. “TB is very common, as approximately a quarter of the world’s population is infected with TB,” Prof. Vasankari stated. “We do not have a direct measurement tool for M. tuberculosis infection, which makes it hard to identify patients.” Another issue is the lack of signs and symptoms of latent TB infection. Still, the identification of people with latent TB infection is an important goal of TB elimination. “Treatment of latent TB infection can prevent the development of TB disease and can stop the further spread of TB [1].”

Targeted testing can be used as a TB control strategy to identify and treat persons at high risk for latent TB infection, and those at high risk for developing TB disease once infected with M. tuberculosis. “If you decide to use targeted testing, then you decide to treat,” Prof. Vasankari said. “TB testing activities should only be performed when there is a plan for follow-up or care. This means that healthcare workers should only test those individuals who are at high risk; people not at high risk should generally not be tested.” Targeted groups for testing include pregnant women from high endemic areas who have a positive interferon-gamma release assay (IGRA), and have arrived in a Nordic country within 2 years, and/or have other diseases, and/or pulmonary X-ray indicates previous TB infection, and/or are newly exposed to contagious TB. Patients planned for immunosuppressive treatment or organ transplantation who have a positive purified protein derivative or IGRA, and/or pulmonary X-ray indicates previous TB infection, and/or epidemiological history indicates a high risk of previous exposure also qualify for testing. The same is true for patients with HIV and a positive purified protein derivative or IGRA. Latent TB infection can be diagnosed by using the Mantoux tuberculin skin test and IGRAs which measure a person’s immune reactivity to M. tuberculosis.

Prof. Vasankari emphasised that anyone with TB symptoms or a positive Mantoux tuberculin skin test or IGRA result should be medically evaluated for TB disease. “This includes taking the medical history, a physical examination, a test for TB infection, a chest X-ray, and a bacteriological examination.” Regarding drug treatment, the currently approved regimens are daily isoniazid monotherapy for 6–9 months, daily rifampicin plus isoniazid for 3 months, daily rifampicin monotherapy for 4 months, daily rifapentine plus isoniazid for 1 month, and weekly rifapentine plus isoniazid for 3 months [2,3].

1. Sterling TR, et al. MMWR Recomm Rep. 2020;69(1):1–11.


2. WHO consolidated guidelines on tuberculosis. Module 4: Treatment drug-susceptible tuberculosis treatment. 2021.


3. Vasankari T. Latent tuberculosis-an update. Nordic Lung Congress 2022, 01–03 June, Copenhagen, Denmark.

 

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Posted on 8 June, 2022