Contact- and index case characteristics associated with IGRA positivity in close contacts of pulmonary tuberculosis in Brazil: a multicenter cohort

Identifying Mycobacterium tuberculosis infection in close contacts is central to TB control, yet evidence on factors associated with interferon-gamma release assay (IGRA) positivity in high-burden settings is limited. This study assessed contact- and index case characteristics associated with IGRA positivity in the multicenter RePORT-Brazil cohort. Close contacts were defined as individuals with four hours per week of exposure to a tuberculosis case. IGRA testing was performed at baseline and six months, and associations were estimated using mixed-effects regression models accounting for clustering by index case. Among 1,234 close contacts, 534 (43.2%) tested IGRA positive during follow-up. Higher odds of positivity were associated with older age (adjusted odds ratio [aOR] per 10-year: 1.19; 95%CI: 1.08–1.32), non-white race (aOR: 1.81; 95%CI: 1.22–2.70), lower neutrophil count (aOR per 1,000 cells/µL: 0.91; 95%CI: 0.83–0.99) and current tobacco use (aOR: 1.77; 95%CI: 1.15–2.73). Index case characteristics included cavitation on chest radiography (aOR: 1.81; 95%CI: 1.26–2.59), history of TB (aOR: 0.54; 95%CI: 0.34–0.88), and non-white race (aOR: 1.60; 95%CI: 1.02–2.48). Neither contact nor index case BMI was associated with IGRA positivity. These findings identify clinical and social factors associated with IGRA positivity among close contacts, refining the risk profile of this high-priority group.