Impact of Diabetes Mellitus in TB Patients on TB Transmission.

BACKGROUND: Diabetes mellitus (DM) increases the risk of tuberculosis (TB) progression and poor treatment outcomes. Rising global DM prevalence presents an emerging threat to TB control. We sought to determine whether DM affects TB transmissibility. METHODS: From 2009 to 2012, we enrolled 3109 microbiologically confirmed pulmonary TB patients and their 12 767 household contacts (HHCs) whom we followed for 1 year for the occurrence of TB infection as measured by a tuberculin skin test and for TB disease. We assessed the association between index patient DM and TB infection and disease occurrence in HHCs. RESULTS: The DM status of index patients was not associated with TB infection among child HHCs (adjusted prevalence rate ratio [aPRR], 1.05; 95% CI: 0.78-1.42) or with incident TB infection at 6 months among HHCs uninfected at baseline (adjusted cumulative rate ratio [aCRR], 0.85; 95% CI: 0.66-1.09). Among the 12 442 HHCs without TB disease at baseline, 368 (3.0%) developed TB during the 12-month follow-up. HHCs exposed to an index TB patient with DM had a reduced incidence of TB disease (aCRR = 0.33, 95% CI: 0.13-0.85). CONCLUSIONS: In this cohort study, diabetes mellitus in index patients did not increase the risk of TB infection among HHCs and was instead associated with a substantially lower risk of incident TB disease. These findings challenge the prevailing assumption that DM uniformly amplifies transmission due to its association with smear positivity and cavitary disease, suggesting that its influence on TB dynamics may be more complex than previously understood.