Role of tuberculosis symptoms in transmission risk to cell contacts in prisons

Understanding determinants of Mycobacterium tuberculosis transmission is critical to devising effective strategies to reduce its burden. Whether and to what extent symptoms influence transmission remains poorly understood.

Between 2020 and 2022, we systematically screened persons deprived of liberty (PDL) from three prisons in Brazil for tuberculosis (TB) by symptom assessment and sputum testing with Xpert MTB/RIF Ultra. We performed QuantiFERON-TB Gold Plus (QFT) testing among cell contacts of individuals with TB and in cells with no TB case identified. We evaluated the relationship between TB exposure (symptomatic, asymptomatic and none) and QFT positivity using Bayesian generalised linear mixed models.

We screened 7641 PDL for TB and identified 290 cases, yielding a prevalence of 3.8% (290/7641). After applying the exclusion criteria, 686 participants were included for the QFT analysis: 132 contacts of 42 individuals with symptomatic TB, 224 exposed to 52 individuals with asymptomatic TB and 330 with no recent cell exposure. The odds of QFT positivity were higher in symptomatic (adjusted OR (aOR) 2.50, 95% credible interval (CrI) 1.51 to 4.16) and asymptomatic (aOR 1.61, 95% CrI 1.06 to 2.45) exposure groups than in those unexposed. QFT positivity in contacts of symptomatic and asymptomatic TB did not differ (aOR 1.56, 95% CrI 0.92 to 2.63). These associations may be underestimated because of infections acquired outside cell assignments.

Approximately two-thirds of individuals with TB lacked symptoms, and their contacts and symptomatic TB contacts had similarly increased risk of QFT positivity compared with individuals without recent cell exposure. These findings indicate that symptom-based screening misses many TB cases. Effective TB control requires systematic screening irrespective of symptoms to interrupt transmission and accelerate diagnosis in high-burden settings.