The results of this nationwide retrospective observational cohort study showed a significantly higher risk of hospitalization, ICU admission/intubation, and mortality in patients with T1DM than in non-diabetic patients. Also, the results revealed that patients with T1DM have an approximately 3-fold higher risk of ICU admission/mechanical ventilation and mortality when compared to patients with T2DM. The risk remained higher even after the results were adjusted for age, gender, micro-vascular and macro-vascular complications. To our knowledge, this is one of the most comprehensive studies conducted so far, on COVID-19 in patients with T1DM.
There are a number of studies in the literature showing the relationship between COVID-19 disease and T2DM. Most of these studies reported that COVID-19 disease is quite common among T2DM patients, and generally, with a more complicated course [5–7]. Very few studies have been published on COVID-19 in patients with T1DM, however, similar findings to T2DM have been reported [15–17, 19, 22]. The low prevalence of T1DM in the general population, the relatively younger age of T1DM patients compared to T2DM patients, and the fact that COVID-19 infection affects older patients rather than younger ones are among the proposed reasons for the scarcity of data on T1DM [23, 24].
We observed a 16% overall risk of mortality rate in COVID-19 patients with T1DM. Compared to the 1.8% mortality in the non-diabetic population in the same dataset, such an increased risk deserves special attention as it seems the highest number reported so far. The rate of mortality in the CORONADO study was 5.4% [22], while one multicenter and another small-scale study from the United States reported 9% and 3% death rates in COVID-19 patients with T1DM, respectively [17, 18]. Also, a more recent whole-population study from England reported a 3.5% death rate among T1DM patients [16, 20]. Higher mortality of patients with T1DM in our study may be explained by the increased burden of comorbidities. In a national registry from England [20] patients with T1DM who died due to COVID-19 had markedly higher rates of comorbidities including cardiovascular or renal comorbidities by 62.3%, heart failure by 23.9%, and stroke by 11.0%. T1DM patients in our study had even a more severe comorbidity burden, such as coronary artery disease, chronic kidney disease, and heart failure by 39.9%, 54.4%, and 23.3%, respectively. Almost half of these patients had at least one microvascular complication.
In addition to the mortality outcome, the risk of hospitalization in the present study seems to be the highest among similar publications in the literature. Overall, six out of ten patients with T1DM in our study were hospitalized following COVID-19 diagnosis. Previous studies from different countries reported the hospitalization rates in patients with T1DM between 21.9% and 51%. Also, almost one-third of our patients were admitted to the ICU, which was recorded by 5–23% in other studies from different countries [17, 24, 25]. In the CORONADO study, 19.6% of patients with T1DM required mechanical ventilation [22]. Not surprisingly, the risk of a more severe COVID-19 course was higher in the T1DM population with a higher burden of significant comorbidities.
The present study compared T1DM and T2DM patients in terms of mortality and other prognostic factors using three different PSM models. In all models, the mortality rate was significantly higher in patients with T1DM, while there was no significant difference in the hospitalization, ICU admission, and intubation rates. Few studies so far have compared patients with T1DM and T2DM in terms of COVID-19 severity and mortality. One study reported fewer deaths in patients with T1DM compared to patients with T2DM (5.4% vs 10.6%), although the analysis was limited to 56 patients with T1DM [22]. In addition, there were significant differences in age and gender between the T1DM and T2DM groups. Another study from the UK reported that the odds of mortality from COVID-19 was 3.5 times higher in patients with T1DM and 2.0 times higher in those with T2DM relative to non-diabetic patients [16]. In our three PSM models, T1DM and T2DM groups were matched for age and gender, and the median age in both groups was 41 years. Albeit the data on the duration of diabetes duration was not available in our study, it is well-known that is typically longer in individuals with T1DM than those with T2DM of the same age because the onset of diabetes is much earlier in T1DM. Thus, one major reason for the increased mortality in patients with TIDM might be the longer duration of diabetes. Also, the median HbA1c level in patients with T1DM in the present study was significantly higher than the patients with T2DM. The risk of mortality from COVID-19 was reported higher at markedly increased HbA1c levels in both T1DM and T2DM in a recent study from England [20]. Therefore, poor glycemic control may also be involved in the mechanism of increased mortality in our study. For this reason, we conducted a further comparison of age, gender, HbA1c levels, and microvascular and macrovascular complications between the matched groups of T1DM and T2DM. The results showed that patients with T1DM had higher mortality rate independent of HbA1c levels and complications. These findings suggest that T1DM and T2DM are completely different diseases and different immune dysfunctions in patients with T1DM may induce higher mortality rates in these patient groups.
Numerous studies have repeatedly identified older age as a significant factor in the course of COVID-19, not only in T2DM [26–28] but also in T1DM [16, 20, 24]. Our findings are consistent with the earlier findings that in COVID-19 patients with T1DM, age is a strong predictor of mortality and poor prognosis as well. Likewise, we identified lymphopenia as a predictor of worse prognosis in the T1DM group, which is in line with the previous reports from others [7, 29, 30]. In this regard, T1DM patients with older age and lymphopenia should be treated more carefully during COVID-19.
Several limitations of the present study should be acknowledged. First, its observational design precludes establishing a causal relationship between the type of diabetes and outcomes. Second, all patients included in the study had confirmed diagnosis of COVID-19 (PCR Positive). The lack of symptomatic but unconfirmed COVID-19 cases or patients with false-negative COVID-19 PCR results may reduce the generalizability of our findings. Third, some data were unavailable in the dataset, such as duration of diabetes and insulin doses, which could be important factors to predict prognosis. And finally, the low number of patients with Type 1 diabetes can be considered as a limitation. One major strength of this study is its population-based, nationwide design. Also, to our knowledge, this study is the most comprehensive report of COVID-19 outcomes in adult patients with T1DM.
In conclusion, COVID-19 patients with T1DM have higher mortality rate than non-diabetic patients and those with T2DM. This increased mortality rates in patients with T1DM appear to be independent of age, gender, glycemic control, and complications; suggesting that T1DM and T2DM have different pathophysiological mechanisms. Therefore, patients with T1DM seem to be particularly disadvantaged during the COVID-19 pandemic, suggesting some prioritization needs for prevention and care.