How can we achieve better prevention of progression to tuberculosis among contacts?

Strategies for control and elimination of tuberculosis (TB) in low-incidence settings are directed toward treatment of recently acquired latent tuberculosis infection (LTBI) in TB contacts [1]. To identify this target population for preventive treatment the development of more specific, in vitro assays for LTBI, the interferon (INF)-c release assays (IGRAs), has offered an alternative method for LTBI diagnosis. Although IGRAs are increasingly recommended in national guidelines, evidence that positive IGRA results are prognostic for developing TB is still limited [2, 3], especially outside of prospective studies with welldefined inclusion criteria. Therefore, we investigated progression towards active TB among IGRA positive contacts of active TB cases under routine field conditions and calculated the positive predictive value (PPV) for progression and the number needed to treat (NNT) with preventive treatment to prevent one incident TB case. Additionally, we introduced different cut-off values for IGRA positivity and compared the computed progression rates. Among all contacts with a positive tuberculosis-specific IGRA we describe the uptake of preventive treatment.