Impact of Diabetes Mellitus in TB Patients on TB Transmission [TBN 088]

A longitudinal analysis evaluated whether diabetes mellitus (DM) in patients with microbiologically confirmed tuberculosis (TB) affects TB transmissibility to household contacts (HHCs) and the risk of TB disease development among exposed contacts. The study was embedded within a prospective cohort conducted between September 2009 and August 2012 across 20 districts in Lima, Peru. The investigators hypothesized that if DM increased infectiousness, household contacts of TB patients with DM would have higher rates of TB infection and might develop disease earlier than contacts of TB patients without DM.

The study systematically enrolled all newly diagnosed TB patients aged 16 years or older presenting to participating health clinics, avoiding convenience sampling. TB diagnoses were confirmed by sputum smear microscopy and mycobacterial culture. Household contacts were visited within 2 weeks of index patient diagnosis and were evaluated for TB symptoms. Baseline TB infection was assessed using the tuberculin skin test (TST), except among contacts with co-prevalent TB, prior TB disease, or a previous positive TST. Follow-up assessments occurred at 6 and 12 months. Index patients were classified as having DM based on self-reported prior diagnosis or use of hypoglycemic medication. Serum fructosamine levels were additionally measured in 1,523 randomly selected smear-positive index patients to assess recent glycemic control. The analysis included 12,767 HHCs of 3,109 microbiologically confirmed TB patients; DM status was available for 3,083 index patients, of whom 173 (5.6%) had DM.

Index TB patients with DM were more likely to be sputum smear-positive than those without DM (80.2% vs 72.5%, P = .03), suggesting potentially greater bacillary burden. However, among 4,259 child HHCs with known baseline infection status, exposure to a DM index patient was not associated with a higher prevalence of TB infection at baseline (adjusted prevalence risk ratio [aPRR] 1.05, 95% CI 0.78-1.42). Results remained similar across multiple sensitivity analyses, including alternative DM definitions based on fructosamine levels, adjustment for Mycobacterium tuberculosis lineage, restriction to older index patients, and stratification by metformin use. Among 4,812 initially uninfected HHCs, exposure to a DM index patient was not associated with increased incident TB infection during follow-up (adjusted cumulative rate ratio [aCRR] 0.85, 95% CI 0.66-1.09), and all sensitivity analyses yielded similar null findings. 

In contrast, among 12,442 HHCs free of TB disease at enrollment, 368 (3.0%) developed incident TB disease over 12 months. Contacts exposed to TB patients with DM had a substantially lower risk of developing incident TB disease than contacts exposed to TB patients without DM (aCRR 0.33, 95% CI 0.13-0.85), representing approximately a two-thirds reduction in risk. This association remained generally consistent across sensitivity analyses, including alternative DM classifications, adjustment for M. tuberculosis lineage and isoniazid preventive therapy use, and restriction to index patients aged 40 years or older. Among the subgroup of contacts exposed to DM index patients, contacts who themselves had DM showed numerically higher rates of incident TB infection (6.7% vs 2.2%) and incident TB disease (3.3% vs 0.8%) than contacts without DM, although neither comparison reached statistical significance.

TB patients with DM were more likely to be smear-positive but did not appear to transmit TB infection more frequently to household contacts. Unexpectedly, household contacts exposed to TB patients with DM had a lower risk of developing incident TB disease during follow-up. As an observational cohort study, the findings are susceptible to residual confounding and cannot establish causality. The apparent protective association for incident TB disease warrants further investigation to determine whether it reflects biological mechanisms, differences in contact patterns, treatment-related factors, or unmeasured confounding.

Source: Huang CC, Tan Q, Becerra MC, Calderon R, Contreras C, Howard NC, Lecca L, Jimenez J, Madden AE, Yataco R, Galea JT. Impact of Diabetes Mellitus in Tuberculosis (TB) Patients on TB Transmission. Clinical Infectious Diseases. 2026 May 15;82(5):829-40.