Background: The authors aimed to determine whether, and by how much, diabetes mellitus (DM) increases the risk of tuberculosis (TB) and conversely whether TB increases the risk of DM.
Methods: Retrospective cohort analyses using data from two Oxford Record Linkage Study (ORLS) datasets, containing information on hospital admissions and day-case care between 1963 and 1998 (ORLS1) and between 1999 and 2005 (ORLS2), were carried out. The rate ratio (RR) for tuberculosis after admission to hospital with diabetes and for diabetes after hospital admission with tuberculosis was calculated.
Results: In ORLS1, the RR for TB in people admitted to hospital with DM, comparing the latter with a reference cohort, was 1.83 (95% CI 1.26 to 2.60), and in ORLS2 the RR was 3.11 (1.17 to 7.03). RRs for pulmonary tuberculosis (PTB) and extrapulmonary tuberculosis (EPTB) within ORLS1 were similar at, respectively, 1.80 (1.16 to 2.67) and 1.98 (0.88 to 3.92). In ORLS 2 the RR for PTB was 2.63 (0.91 to 6.30). In ORLS1, there was no indication that TB was a risk factor for DM (RR 1.12, 0.76 to 1.60). The ORLS2 dataset was too small to analyse whether TB led to DM.
Discussion: DM was associated with a two- to threefold increased risk of TB within this predominantly white, English population. The authors found no evidence that TB increases the risk of DM. Our findings suggest that the risks of PTB and EPTB were both raised among individuals with DM. As DM prevalence rises, this association will become increasingly important for TB control and treatment.