Silent TB in Prisons: Symptoms Miss Many Infectious Cases

Tuberculosis transmission drives the disease’s heavy toll, but researchers still debate how much symptoms matter for spreading infection. To probe this question in a high-risk setting, a team led by corresponding author Júlio Croda carried out systematic screening inside three prisons in Brazil between 2020 and 2022. They screened people deprived of liberty (PDL) using symptom assessment and sputum testing with Xpert MTB/RIF Ultra, aiming to find active TB cases regardless of whether individuals reported coughing or other classic signs. At the same time, the team measured recent TB exposure among cell contacts by performing QuantiFERON-TB Gold Plus (QFT) testing, including contacts of people diagnosed with TB and people housed in cells where no TB case was identified. The study compared three exposure categories—contacts of symptomatic TB cases, contacts of asymptomatic TB cases, and people with no recent cell exposure—so the researchers could see whether silent, asymptomatic cases were contributing to transmission. To analyze these relationships while accounting for the clustered prison environment, they used Bayesian generalized linear mixed models.

The screening effort reached 7,641 PDL and identified 290 tuberculosis cases, a prevalence of 3.8% (290/7,641). For the QFT analysis, after applying exclusion criteria, 686 participants were included: 132 contacts of 42 individuals with symptomatic TB, 224 individuals exposed to 52 individuals with asymptomatic TB, and 330 individuals with no recent cell exposure. The team compared QFT positivity across those groups. Using Bayesian generalized linear mixed models, they found that odds of QFT positivity were higher in contacts of symptomatic TB (adjusted odds ratio [aOR] 2.50, 95% credible interval [CrI] 1.51–4.16) and also higher in contacts of asymptomatic TB (aOR 1.61, 95% CrI 1.06–2.45) compared with people who had no recent cell exposure. When directly comparing contacts of symptomatic versus asymptomatic cases, QFT positivity did not differ significantly (aOR 1.56, 95% CrI 0.92–2.63). Importantly, the study notes that over half of people with TB in the screened population lacked symptoms.

These findings carry a clear message for TB control in crowded, high-burden settings: relying on symptoms alone misses many infectious people and underestimates transmission risk to their contacts. Because contacts of asymptomatic cases showed increased QFT positivity comparable to contacts of symptomatic cases, symptom-based screening will not catch a large portion of potentially infectious individuals inside prisons. The results support systematic, routine testing strategies that do not depend solely on people reporting cough or other signs, using tools such as Xpert MTB/RIF Ultra to identify active disease and QuantiFERON-TB Gold Plus (QFT) to detect recent infection among contacts. By accelerating diagnosis and identifying infections that symptom checks would miss, such approaches could shorten the time infectious individuals remain undetected, reduce onward transmission in cells, and guide targeted public health responses where TB burden is high. The study underscores the need to rethink screening policies in closed settings to prevent silent spread.