Tuberculosis and diabetes in low and moderate tuberculosis incidence countries

In countries with low and moderate incidence of tuberculosis (TB), the disease tends to concentrate in specific high-risk populations such as people with diabetes mellitus (DM). We review the updated evidence on the association between 1) DM and active TB, and 2) DM and latent tuberculous infection (LTBI), and 3) we summarize the findings on the population-level impact of DM on TB epidemiology, with particular focus on low- and moderate-incidence settings. We conducted an updated review of studies on DM and active TB, and found 11 more cohort studies published after the previous systematic review from 2008. The updated pooled relative risk (RR) (2.03, 95%CI 1.62-2.55) of all the studies was substantially lower than the three-fold risk increase in the previous review. Substantial heterogeneity of RR across studies was found. Possible reasons for such heterogeneity include different levels of residual confounding, the effect of modification by age, and different levels of glycemic control in the population. In a recently published systematic review on DM and LTBI, one cohort study and 12 cross-sectional studies were identified. The results from cross-sectional studies suggest a significant but modestly increased risk of LTBI among patients with DM (pooled odds ratio 1.18, 95%CI 1.06-1.30). We reviewed evidence on the population-level impact of DM on TB epidemiology in studies using population-attributable fraction analysis and infectious disease modelling. Those studies revealed that DM accounted for a substantial TB burden in low- and moderate-incidence countries. Finally, we discussed the complex association of obesity, DM and TB risk and the impact of the global obesity pandemic on TB epidemiology.