Detect early TB infection, evaluate contacts for TB (DETEC-TB) – a protocol for a prospective cohort study on active case finding for tuberculosis disease and tuberculosis infection source tracing

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BACKGROUND: Tuberculosis (TB) is a leading cause of death from infectious disease, with 1.25 million deaths in 2023. Among the estimated 10.8 million people who developed TB in 2023, only 75% were diagnosed and reported to national programs and the World Health Organization (WHO). Tanzania has one of the highest burdens of TB in the world, with an estimated 29% of cases unreported. Innovative control strategies, including improved active case finding, are needed to close this gap. This study aims to determine the proportion of persons with TB disease among contacts of adolescents with newly-acquired TB infection and the cost-effectiveness of this strategy. METHODS: This 5-year prospective cohort study will perform serial Interferon Gamma Release Assay (IGRA) T-SPOT.TB testing for TB infection among 1200 adolescent school children aged 13 to 15 years in Dar es Salaam, Tanzania. Participants with negative T-SPOT.TB test at baseline will repeat T-SPOT.TB testing every 4 months for 16 months to detect new TB infections. Participants will then be categorized into three groups based on T-SPOT.TB test results: prevalent TB infection ( IGRA positive at baseline), incident TB infection (conversion from IGRA-negative to IGRA-positive at follow-up), or no TB infection (persistent IGRA-negative). Household and other close contacts of 100 adolescents (4 contacts each) selected from the three categories will be tested to detect TB disease source cases. Tests will include expectorated sputum for gene X-pert and chest radiography. Data will be analyzed using Stata version 16, with the chi-square test used to compare differences in proportions of TB disease cases among contacts in each category. Logistic regression analysis will be used to estimate the odds ratios for the probability of source cases of tuberculosis disease among close contacts. A multivariate logistic regression model will adjust for potential confounders. A micro-costing approach will be used to determine the cost-effectiveness of this strategy for identifying community transmission of TB. DISCUSSION: The DETEC-TB study proposes a novel approach to active tuberculosis case finding and infection source tracing. Serial T-SPOT.TB testing of adolescents will detect prevalent and incident TB infections. Close contacts of these adolescents will be tested to identify cases of infectious TB disease that may have transmitted the infection.

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