Originally published by 2 Minute Medicine® (view original article). Reused on AccessMedicine with permission.

1. The incidence of chilblains increased during the COVID-19 pandemic, but chilblains cases were only weakly associated with COVID-19 infection, with only 2.0% of patients testing positive for COVID-19.

Evidence Rating Level: 2 (Good)

Chilblains refer to lesions of the skin related to inflammation from cold, damp conditions. During the start of the COVID-19 pandemic, dermatologists noticed an uptick in cases of chilblains, which presented within the 30 days after COVID-19 infection was confirmed in patients. This retrospective cohort study based aimed to determine the incidence of chilblains in the first 9 months of the pandemic, and assess whether a correlation between chilblains cases and COVID-19 infection existed. Data from Northern California’s medical records (with 4.4 million patients) were analyzed to track COVID-19 and chilblains cases. The study dates were from March to December of 2020 to encompass the pandemic months, and March to December of the years 2016-2019 to act as controls. The study found that the incidence of chilblains cases was higher during the pandemic. There were 780 cases in the 9 pandemic months, and 539 in the 36 month control period: This translated to an annual incidence of 28.6 per 100,000 person-years (95% CI 26.8-30.4) during the pandemic and 5.2 (95% CI 4.8-5.6) before the pandemic. However, the incidence of chilblains was higher in youth 13-19 years of age, whereas the highest COVID-19 incidence rate came from adults 20-59 years of age. When examining differences by race, the highest chilblains incidence rates were in Asian Americans (42.5, 95% CI 37.7-47.8), but the highest COVID-19 incidence was found in the Latinx population (62.5, 95% CI 61.9-63.1). The correlation coefficient for the chilblains and COVID-19 infection association was 0.18 (p = 0.01), which was determined to be a weak association. Only 2.0% of chilblains patients had a positive test result for COVID-19 within 6 weeks of chilblains diagnosis. Overall, although the incidence of chilblains increased drastically during the pandemic, the correlation between chilblains cases and COVID-19 infection is weak, with very few chilblains patients contracting COVID-19. The increased incidence could therefore be due to behavioural changes as a result of the lockdown, as opposed to being a secondary effect of COVID-19 infection.]

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