Much of our initial understanding of the increased risk of serious COVID-19 infection in people with diabetes is based on data from the previous SARS, MERS and H1N1 influenza epidemics. Mortality rates as high as 16% have been reported from China in those with diabetes and COVID-19, compared to 1–2% in those without any co-morbidities (Guo et al, 2020).
Of concern is the fact that people with diabetes may initially have a milder presentation of COVID-19, with fewer classical symptoms of fever, chest tightness or dyspnoea. This is comparable to the lack of symptoms in the “silent myocardial infarction” sometimes seen in people with diabetes. In a commentary published on 31 March, Ernesto Maddaloni and Raffaella Buzzeti, from Sapienza University of Rome, suggest that this may cause a life-threatening delay in diagnosis and treatment, and they warn us not to underestimate the COVID-19 severity in people with diabetes who initially have mild symptoms.
There are far more questions than answers. The authors explore potential reasons for the increased severity. People with diabetes already have low-grade inflammation; might that facilitate a cytokine storm, which increases fatality? Could these changes, such as increased levels of interleukin-6, be specifically targeted with drug therapies used in autoimmune conditions, as is being trialled in some Italian hospitals to fight COVID-19?
The authors also share some of the unanswered questions from the original data coming out of China (Guo et al, 2020). Does COVID-19 have a different impact in those with type 1 compared with type 2 diabetes? Do the drugs we use to treat diabetes have differential effects on COVID-19 disease progression? Is the impact of ageing the same in those with diabetes as in the general population?
The commentary highlights that the relationship between COVID-19 and diabetes appears to be bidirectional, with COVID-19 infection worsening pre-existing diabetes or even predisposing to diabetes in people without the condition. What is not clear is whether this impact may continue over the longer term after the acute infection. Only monitoring of the long-term impact in those with diabetes who have had COVID-19 will answer this.
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