Previous studies that have found an increased risk for tuberculosis (TB) in people with diabetes mellitus (DM) have been conducted in segments of the population and have not adjusted for important potential confounders. We sought to determine the RR for TB in the presence of DM in a national population with data on confounding factors in order to inform the decision-making process about latent tuberculosis infection (LTBI) screening in people with diabetes.
Whole population historical cohort study.
All Australian States and Territories with a mean TB incidence of 5.8/100 000.
Cases of TB in people with DM were identified by record linkage using the National Diabetes Services Scheme Database and TB notification databases for the years 2001–2006.
Primary and secondary outcome measures
Primary outcome was notified cases of TB. Secondary outcome was notified cases of culture-confirmed TB. RR of TB was estimated with adjustment for age, sex, TB incidence in country of birth and indigenous status.
There were 6276 cases of active TB among 19 855 283 people living in Australia between 2001 and 2006. There were 271 (188 culture positive) cases of TB among 802 087 members of the DM cohort and 130 cases of TB among 273 023 people using insulin. The crude RR of TB was 1.78 (95% CI 1.17 to 2.73) in all people with DM and 2.16 (95% CI 1.19 to 3.93) in people with DM using insulin. The adjusted RRs were 1.48 (95% CI 1.04 to 2.10) and 2.27 (95% CI 1.41 to 3.66), respectively.
The presence of DM alone does not justify screening for LTBI. However, when combined with other risk factors for TB, the presence of DM may be sufficient to justify screening and treatment for LTBI.
National, general population-based, historical cohort study to estimate the risk of tuberculosis (TB) among people with diabetes mellitus (DM).
Adjustment for important potentially confounding risk factors including age, sex, indigenous status and TB incidence in country of birth.
Overall, people with DM have a 1.5-fold increased risk of developing TB.
The risk for TB is higher among people who are using insulin for DM.
DM accounts for a small proportion of cases of TB in a low TB incidence setting.
Strengths and limitations of this study
The strengths of this study are the cohort design, the large population size, the general population base for the study cohort and the adjustment for important potential confounders, especially TB incidence in the country of birth.
The study limitations are the unavailability of laboratory results to indicate if blood glucose levels were well or poorly controlled in people with DM and the inability to reliably distinguish between type 1 and type 2 DM in this data source.