People with immunoreactivity to tuberculosis are thought to have lifelong asymptomatic infection and remain at risk for active tuberculosis. Marcel A Behr and colleagues argue that most of these people are no longer infected

Key messages

  • Two billion people worldwide are thought to be asymptomatically (latently) infected with Mycobacterium tuberculosis and at risk of developing active tuberculosis (TB)

  • The prevalence of latent TB infection is inferred from tests that detect immunoreactivity to mycobacterial antigens rather than live bacteria and from mathematical modelling

  • Longitudinal studies and clinical trials show that this TB immunoreactivity can persist after curative treatment

  • Most people with TB immunoreactivity do not develop active TB upon immunosuppression, suggesting that they have cleared their infection while retaining immunological memory to it

  • TB immunoreactivity cannot distinguish cleared from persistent infection, emphasising the urgent need for tests that can identify people with asymptomatic infections

Read and listen at BMJ…