Type 2 diabetes and the risk of hospitalisation and mortality from seasonal influenza: an observational register-based study in Sweden

Objectives To compare influenza-related hospitalisation, mortality and effects of background factors in adults with type 2 diabetes (T2D) and age-matched and sex-matched controls. To explore associations between clinical variables and the risk of severe influenza outcomes.

Design Register-based nationwide cohort study. Settings Data from the National Diabetes Register are cross-linked to the Swedish Population Register, Statistics Sweden and the Swedish Patient Register.

Participants 371 811 patients with T2D from the Swedish National Diabetes Register and 1 728 856 matched control individuals from the Swedish population followed over the 2013/14 - 2018/19 influenza seasons. Primary and secondary outcomes Data on hospital admissions, mortality, socioeconomic factors and pre-existing conditions were collected.

Risk associations were analysed using Cox proportional hazards models. Within the diabetes group, non-linear associations between common clinical variables and influenza hospitalisation were examined.

Results 1.6% of those with diabetes and 1.0% of controls were hospitalised for influenza, with influenza-related mortality at 0.12% and 0.08% respectively. Adjusted HR for hospitalisation in T2D was 1.57 (95% CI 1.52 to 1.61) and 1.44 (95% CI 1.29 to 1.61) for mortality.