Abubakar I, et al. - Researchers conducted this prospective cohort study to determine the predictive values of the tuberculin skin test (TST) and two interferon-γ release assays (IGRAs) for the development of active tuberculosis in high-risk groups (ie, people in recent contact with active tuberculosis cases and from high-burden countries). Study results suggested that, for potential disease progression among high-risk groups, IGRA-based or BCG-stratified TST strategies seem most suited for screening.

Methods

• Researchers performed this prospective cohort study recruiting participants from 54 centers (eg, clinics, community settings) in London, Birmingham, and Leicester in the United Kingdom.
• Eligible individuals were those aged ≥ 16 years who were at high risk for latent tuberculosis infection (ie, recent contact with someone with active tuberculosis [contacts] or were migrant who had arrived in the United Kingdom in the past 5 years from—or who frequently travelled to—a country with a high burden of tuberculosis [migrants]).
• They excluded prevalent cases of tuberculosis, and participants who were treated for latent tuberculosis after a positive test result.
• Three tests were performed on each participant (QuantiFERON-TB Gold-In Tube, T-SPOT.TB, and a Mantoux TST).
• They reported a positive TST result using three thresholds: 5 mm (TST-5), 10 mm (TST-10), and greater than 5 mm in BCG-naive or 15 mm in BCG-vaccinated (TST-15) participants.
• From recruitment to development of tuberculosis or censoring, they followed up the participants.
• By national tuberculosis databases, telephone interview, and review of medical notes, they identified incident tuberculosis cases.
• The prognostic value of IGRAs compared with TST was estimated primarily; it was assessed by the ratio of incidence rate ratios and predictive values for tuberculosis development.

Results

• Researchers recruited 10,045 people between May 4, 2010, and June 1, 2015; of these, 9,610 (4,861 [50.6%] contacts and 4,749 [49.4%] migrants) were eligible for inclusion.
• They followed the participants for a median of 2.9 years (range: 21 days to 5.9 years).
• Active tuberculosis developed in 97 (1.0%) of 9,610 participants (77 [1.2%] of 6,380 with results for all three tests).
• Those who tested negatively in all tests showed very low annual incidence of tuberculosis (ranging from 1.2 per 1,000 person-years, 95% CI 0.6–2.0 for TST-5 to 1.9 per 1,000 person-years, 95% CI 1.3–2.7, for QuantiFERON-TB Gold In-Tube).
• Among the participants who tested positively, annual incidence was highest for T-SPOT.TB (13.2 per 1,000 person-years, 95% CI 9.9–17.4), TST-15 (11.1 per 1,000 person-years, 8.3–14.6), and QuantiFERON-TB Gold In-Tube (10.1 per 1,000 person-years, 7.4–13.4).
• Positive results for these tests had significantly higher predictive value for progression than TST-10 and TST-5 (eg, ratio of test positivity rates in those progressing to tuberculosis vs those not progressing T-SPOT.TB vs TST-5: 1.99, 95% CI 1.68–2.34; P < 0.0001).
• However, a higher proportion of participants who progressed to active tuberculosis (64 [83%] of 77 tested) was identified by TST-5 than all other tests and TST thresholds (≤ 75%).