Association between influenza and the incidence rate of new-onset type 1 diabetes in Japan.

AIM This study aimed to determine whether there is an association between influenza and new-onset type 1 diabetes. MATERIALS AND METHODS This population-based retrospective cohort study used data from the National Database of Health Insurance Claims and Specific Health Check-ups of Japan. Influenza was defined based on drug prescriptions and the onset of type 1 diabetes was defined using specific medical codes indicating a type 1 diabetes diagnosis. We calculated the incidence rate ratio of new-onset type 1 diabetes within 180 days after an influenza diagnosis and compared it with that at other times using Poisson regression and generalized estimating equations. Sensitivity analyses were performed to confirm the robustness of this finding. RESULTS We analyzed the data of 10,400 patients with new-onset type 1 diabetes, including 2,196 (952 male 1,244 female) patients diagnosed with influenza between September 1, 2014 and August 31, 2017. Although only patients with type 1 diabetes were included, adjusted analysis showed that individuals had a 1.3-fold (95% confidence interval: 1.15-1.46) higher risk of developing type 1 diabetes in the first 180 days after influenza diagnosis than that at other times. CONCLUSIONS In this Japanese population-based cohort, the risk of new-onset type 1 diabetes may increase after the diagnosis of influenza. These results, which must be confirmed in other populations, suggest that influenza may be a causal factor for new-onset type 1 diabetes. The molecular mechanisms underlying the potential etiological relationship between influenza and type 1 diabetes should be elucidated.