Background: The association between diabetes mellitus (DM) and tuberculosis (TB) has been established on the basis of cross-sectional studies; however, only a few longitudinal studies have been conducted, with inconsistent results.
Objective: To study the effect of ethnicity and the presence and duration of DM on the risk of incident TB based on 15 years of follow-up of the entire Danish population.
Design and methods: Using Poisson regression analysis, we estimated TB incidence in individuals with DM vs. those without DM by linking nationwide DM and TB registers to the National Civil Register at case level.
Results: The TB rate ratio was 1.9 in individuals with DM compared to non-DM individuals, regardless of country of birth, with the exception of African-born individuals (rate ratio 0.5). The risk decreased drastically within the first 2 years after the diagnosis of DM; no association was found with longer durations of DM. The risk also decreased the later the year of DM diagnosis.
Conclusions: The study confirmed DM as a risk factor for TB, except in the case of African-born individuals. Other non-DM risk factors for TB could act as effect-modifiers on the DM-TB association. Implementing earlier DM diagnosis and improving metabolic control may reduce the risk of DM-related TB.