medwireNews: Testing positive for SARS-CoV-2 is associated with an increased risk for incident type 1 diabetes, but this is restricted to the first 30 days post-infection and may be explained by increased testing frequency around the time of diabetes diagnosis, researchers report.
Helen Colhoun (Public Health Scotland, Glasgow, UK) and team analyzed data from 1,849,411 people aged less than 35 years without diabetes at baseline who were included in REACT-SCOT, a matched case–control study including all individuals diagnosed with COVID-19 in Scotland.
As reported in Diabetes Care, 365,080 people had a first diagnosed SARS-CoV-2 infection between March 2020 and November 2021, and 1074 were diagnosed with type 1 diabetes during this period.
Using a model that split person–time into 1-day intervals “[t]o allow exact updating of time-varying covariates—SARS-CoV-2 status and vaccination status,” the researchers found that SARS-CoV-2 infection in the past 30 days was associated with a significantly increased risk for incident type 1 diabetes, with a rate ratio of 2.62. On the other hand, there was no such association after 30 days post-infection.
Discussing these findings, Colhoun et al say that SARS-CoV-2-induced type 1 diabetes could occur within the first 30 days of infection, but believe that “there are strong arguments against a causal effect of COVID-19 underlying this association.”
Firstly, they found an increased frequency of COVID-19 testing in the days before and after type 1 diabetes diagnosis, for both positive and negative results, suggesting “that the association is partly attributable to higher detection of infection” at this time.
In addition, the researchers note that many people with positive COVID-19 tests less than 30 days before diabetes diagnosis were likely to have “already had diabetes by the time of infection,” given that previous research has reported a median lag of 25 days between onset of symptoms and diagnosis of type 1 diabetes in England.
A lack of association between COVID-19 vaccination status and type 1 diabetes incidence provided further evidence against a causal effect of SARS-CoV-2 infection on the development of type 1 diabetes. Colhoun and team caution, however, that the estimated impact of vaccination was “based almost entirely on adults, because few children were vaccinated during the study period,” and that this analysis was insufficiently powered “to detect subtle effects of vaccination.”
The investigators also looked at trends in type 1 diabetes incidence in children aged 0–14 years before and during the pandemic, finding that the incidence in 2020–2021 was approximately 20% higher than the 7-year average for 2015–2021 in Scotland.
They say that the time course of this increase “predated most of the cumulative incidence of infection in this age group” based on estimates from England, again suggesting a lack of causal association between SARS-CoV-2 infection and rates of diabetes.
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Diabetes Care 2022; doi:10.2337/dc22-0385