Risk Assessment of Tuberculosis in Contacts by Interferon-γ Release Assays (IGRAs). A TBNET Study

RATIONAL:Latent infection with Mycobacterium tuberculosis is defined by a positive interferon-γ release assay (IGRA) result in the absence of active tuberculosis.OBJECTIVES:Only few, mostly monocentric studies have evaluated the role of IGRAs to predict the development of tuberculosis in recent contacts in low incidence countries of tuberculosis. We analyzed IGRA results and the effect of preventive chemotherapy on tuberculosis progression rates among recent contacts.METHODS:Results from contact investigations at 26 centers in 10 European countries including testing for latent infection with Mycobacterium tuberculosis by the QuantiFERON-Gold in-Tube (QFT) test or the T-SPOT.TB (TSPOT) were prospectively collected and analyzed.MAIN RESULTS:Among 5020 contacts of 1023 index cases, 25 prevalent secondary cases were identified at screening. Twenty-four incident cases occurred among 4513 contacts during 12326 years of cumulative follow-up. In those with a positive IGRA result, tuberculosis incidence was 0.2 (QFT) and 0 (TSPOT) per 100 patient years when contacts received preventive chemotherapy versus 1.2 (QFT) and 0.8 (TSPOT) per 100 patient years in those not treated (38 and 37 patients needed to be treated to prevent one case, respectively). Positive and negative predictive values were 1.9% (95%CI 1.1-3.0) and 99.9% (95%CI 99.7-100) for the QFT and 0.7% (95%CI 0.1-2.6) and 99.7% (95%CI 99.1-99.9) for the TSPOT.CONCLUSIONS:Tuberculosis rarely developed among contacts and preventive chemotherapy effectively reduced the tuberculosis risk among IGRA-positive contacts. Although the negative predictive value of IGRAs is high, the risk for the development of tuberculosis is poorly predicted by these assays. RATIONAL: Latent infection with Mycobacterium tuberculosis is defined by a positive interferon-γ release assay (IGRA) result in the absence of active tuberculosis.OBJECTIVES: Only few, mostly monocentric studies have evaluated the role of IGRAs to predict the development of tuberculosis in recent contacts in low incidence countries of tuberculosis. We analyzed IGRA results and the effect of preventive chemotherapy on tuberculosis progression rates among recent contacts.METHODS: Results from contact investigations at 26 centers in 10 European countries including testing for latent infection with Mycobacterium tuberculosis by the QuantiFERON-Gold in-Tube (QFT) test or the T-SPOT.TB (TSPOT) were prospectively collected and analyzed.MAIN RESULTS: Among 5020 contacts of 1023 index cases, 25 prevalent secondary cases were identified at screening. Twenty-four incident cases occurred among 4513 contacts during 12326 years of cumulative follow-up. In those with a positive IGRA result, tuberculosis incidence was 0.2 (QFT) and 0 (TSPOT) per 100 patient years when contacts received preventive chemotherapy versus 1.2 (QFT) and 0.8 (TSPOT) per 100 patient years in those not treated (38 and 37 patients needed to be treated to prevent one case, respectively). Positive and negative predictive values were 1.9% (95%CI 1.1-3.0) and 99.9% (95%CI 99.7-100) for the QFT and 0.7% (95%CI 0.1-2.6) and 99.7% (95%CI 99.1-99.9) for the TSPOT.CONCLUSIONS: Tuberculosis rarely developed among contacts and preventive chemotherapy effectively reduced the tuberculosis risk among IGRA-positive contacts. Although the negative predictive value of IGRAs is high, the risk for the development of tuberculosis is poorly predicted by these assays.