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Background
Tuberculosis (TB) remains a major global health problem. A possible risk factor for TB is diabetes (DM), which is predicted to increase dramatically over the next two decades, particularly in low- and middle-income countries, where TB is widespread. This convergence of two epidemics has highlighted the need for a better understanding of the possible association between the two diseases, and its potential significance for public health. This study aimed to assess the strength of the association between TB and DM, using US data.
Methods
A case-control analysis was performed using data from the second National Health and Nutrition Examination Survey (1976–1980). Cases were respondents who had ever been diagnosed with TB (n = 166), and controls were respondents who reported never having been diagnosed with TB (n = 15 191). Exposure to diabetes and intermediate hyperglycaemia was defined using both a self-reported measure, and measures combining self-reported disease with undiagnosed disease identified via an Oral Glucose Tolerance Test (OGTT). Logistic regression analysis, taking into account survey design, was undertaken to estimate an adjusted odds ratio (OR) for the association of TB with diabetes and with intermediate hyperglycaemia, controlling for potential confounding variables – age, gender, race/ethnicity, socio-economic status, household contact with TB, smoking status and BMI.
Results
Depending on the exposure measure used, the crude odds of TB varied between 2.90 (95% CI 1.77 to 4.76) and 3.35 (95% CI 1.96 to 5.74) for people with diabetes compared to those without. Adjustment for potential confounders slightly attenuated the strength of the association; adjusted ORs varied between 2.40 (95% CI 1.43 to 4.01) and 2.60 (95% CI 1.56 to 4.33). No association was found for intermediate levels of glucose intolerance, although the study was underpowered to assess this association.
Conclusions
Irrespective of the exposure measure and the confounders controlled for, diabetes was consistently found to be associated with an increased risk of TB. This study may underestimate the true association between the two diseases, due mainly to exposure misclassification, as only 24.8% of the sample took the OGTT. Due to the inclusion of “ever diagnosed” as opposed to incident TB cases, the direction of the association could not be reliably assessed and may operate in both directions. Some unmeasured factors may have attenuated or increased the relationship, although the majority of known confounders were controlled for. These results may be more generalisable to low TB prevalence populations than to populations where TB is endemic.