Household exposure to symptomatic tuberculosis raises long-term TB risk in South African cohort

People who lived with a household member showing symptoms of tuberculosis faced a significantly higher long-term risk of being diagnosed with TB themselves, according to a historical cohort study published in PLOS Global Public Health.

Of 30,017 participants enrolled in the original ZAMSTAR prevalence survey, 15,887, or 52.9%, could be linked to the PHDC. The analysis focused on 15,471 individuals who did not have prevalent TB at enrolment. Over the subsequent 11 years, 1,819 of them, or 11.8%, developed incident TB.

The study also documented the trajectory of TB in the community.

Exposure status within the household made a clear difference. Over follow-up, individuals who had been exposed to symptomatic TB within their household had the highest cumulative probability of TB diagnosis, at 13% (95% CI: 7.7–18%).

In a multivariable Cox proportional hazards model adjusted for sex and HIV status, people living with a household contact who had symptomatic TB had a higher hazard of TB incidence than those from unexposed households, with an adjusted hazard ratio of 1.53 (95% CI: 1.09–2.13). By contrast, the hazard among those exposed to asymptomatic TB was not significantly elevated, at an adjusted hazard ratio of 1.12 (95% CI: 0.67–1.87).

Sensitivity analyses that restricted follow-up to shorter windows suggested the association with symptomatic exposure was strongest early on. When follow-up was limited to two years, the hazard ratio among people living with a symptomatic household contact was 1.82 (95% CI: 0.97–3.41), and at three years it was 1.73 (95% CI: 0.98–3.10), though these intervals included the null value.

The authors note that the long-term linked cohort demonstrates sustained TB incidence in this high-burden community. They also highlight a practical limitation: incomplete linkage of individuals to the PHDC underscores the need to improve data collection in research studies and to strengthen national patient identification systems so that long-term cohort analyses of this kind can be supported in the future.

Subject of Research: Long-term tuberculosis incidence among household contacts of symptomatic and asymptomatic TB cases in the Western Cape, South Africa

Article Title: Tuberculosis incidence among household contacts of individuals with symptomatic and asymptomatic tuberculosis: A historical cohort study in the Western Cape province of South Africa

Article References: Brown, L. R., Seddon, J. A., Kelly, C., Smith, M., Godfrey-Faussett, P., Dunbar, R., Boulle, A., Roussos, G. A., Claassens, M., & van Schalkwyk, C. (2026). Tuberculosis incidence among household contacts of individuals with symptomatic and asymptomatic tuberculosis: A historical cohort study in the Western Cape province of South Africa. PLOS Global Public Health, 6(10), e0006550. https://doi.org/10.1371/journal.pgph.0006550

Image Credits: AI Generated

DOI: 10.1371/journal.pgph.0006550

Keywords: tuberculosis, household contacts, South Africa, Western Cape, cohort study, ZAMSTAR, HIV, TB incidence, epidemiology, public health, incidence, household