Prior tuberculosis, radiographic lung abnormalities and prevalent diabetes in rural South Africa

Abstract

Background: Growing evidence suggests that chronic inflammation caused by tuberculosis (TB) may increase the incidence of diabetes. However, the relationship between post-TB pulmonary abnormalities and diabetes has not been well characterized.

Methods: We analyzed data from a cross-sectional study in KwaZulu-Natal, South Africa, of people 15 years and older who underwent chest X-ray and diabetes screening with hemoglobin A1c testing. The analytic sample was restricted to persons with prior TB, defined by either (1) a self-reported history of TB treatment, (2) radiologist-confirmed prior TB on chest radiography, and (3) a negative sputum culture and GeneXpert. Chest X-rays of all participants were evaluated by the study radiologist to determine the presence of TB lung abnormalities. To assess the relationships between our outcome of interest, prevalent diabetes (HBA1c ≥6.5%), and our exposure of interest, chest X-ray abnormalities, we fitted logistic regression models adjusted for potential clinical and demographic confounders. In secondary analyses, we used the computer-aided detection system CAD4TB, which scores X-rays from 10 to 100 for detection of TB disease, as our exposure interest, and repeated analyses with a comparator group that had no history of TB disease.

Results: In the analytic cohort of people with prior TB (n = 3,276), approximately two-thirds (64.9%) were women, and the average age was 50.8 years (SD 17.4). The prevalence of diabetes was 10.9%, and 53.0% of people were living with HIV. In univariate analyses, there was no association between diabetes prevalence and radiologist chest X-ray abnormalities (OR 1.23, 95%CI 0.95-1.58). In multivariate analyses, the presence of pulmonary abnormalities was associated with an 29% reduction in the odds of prevalent diabetes (aOR 0.71, 95%CI 0.53-0.97, p = 0.030). A similar inverse relationship was observed for diabetes with each 10-unit increase in the CAD4TB chest X-ray scores among people with prior TB (aOR 0.92, 95%CI 0.87-0.97; p = 0.002), but this relationship was less pronounced in the no TB comparator group (aOR 0.96, 95%CI 0.94-0.99).

Conclusions: Among people with prior TB, pulmonary abnormalities on digital chest X-ray are inversely associated with prevalent diabetes. The severity of radiographic post-TB lung disease does not appear to be a determinant of diabetes in this South African population.

Keywords: Chest imaging; Diabetes; Prior tuberculosis.

Fig. 1

Primary analytic cohort flowchart

Fig. 2

Radiologist Characterization and CAD4TB Score Distribution by Diabetes Status in Individuals with Prior Tuberculosis (TB). Figure 2 A shows the radiologist’s characterization of TB-related abnormalities in chest radiographs, comparing individuals with and without diabetes. Categories include fibrosis, calcification, chronic infiltration, pleural thickening, consolidation, nodules, reticular marks, and other findings. Figure 2B displays the percentage distribution of CAD4TB scores, stratified by diabetes status in patients with a history of TB. Individuals without diabetes had a mean CAD4TB score of 44 (interquartile range, IQR, 27–60), while those with diabetes had a mean score of 40 (IQR 28–54). Statistical analysis using the Kruskal-Wallis Test indicates a significant difference in CAD4TB scores by diabetes status (p = 0.008)