Relation of incident Type 1 diabetes to recent COVID-19 infection: cohort study using e-health record linkage in Scotland

Background Studies using claims databases have reported that SARS-CoV-2 infection >30 days earlier increased the incidence of type 1 diabetes (T1DM). Using exact dates of type 1 diabetes diagnosis from the national register in Scotland linked to virology laboratory data we sought to replicate this finding. Methods A cohort of 1849411 individuals aged <35 years without diabetes, including all those of this age in Scotland who subsequently tested positive for SARS-CoV-2, was followed from 1 March 2020 to 22 November 2021. Incident T1DM was identified by linkage to the national registry. Cox regression was used to test the association of time-updated infection with incident T1DM. Trends in incidence of T1DM in the total population from 2015-2021 were estimated in a generalized additive model. Results There were 365080 in the cohort with at least one detected SARS-CoV-2 infection during follow-up and 1074 who developed T1DM. The rate ratio for incident T1DM associated with first positive test for SARS-CoV-2 (with no previous infection as reference category) was 0.88 (95% CI 0.63 to 1.23) for infection more than 30 days earlier and 2.62 (95% CI 1.81 to 3.79) for infection in the previous 30 days. However negative and positive SARS-CoV-2 tests were more frequent in the days surrounding T1DM presentation. In those aged 0-14 years incidence of T1DM during 2020-2021 was 20% higher than the 7-year average. Conclusions T1DM incidence in children increased during the pandemic. However the cohort analysis does not support a causal effect of SARS-CoV-2 infection itself on T1DM incidence.