Fig. 1: Timeline of events before diagnosis of insulin-dependent diabetes mellitus.

On 14 March 2020, the patient’s parents had returned from a vacation in Austria. Two days later, both parents started to develop COVID-19-typical symptoms (dry cough, shivering, fatigue, dyspnoea, joint pain and loss of smell and taste). No further PCR testing was performed because, at the time, official authorities did not invite them for testing despite both parents having reported their symptoms. On 6 April 2020, their 19-year-old son (the patient in this report) first noticed symptoms related to diabetes mellitus including fatigue, polydipsia and polyuria, which worsened over time. He did not show any typical COVID-19 symptoms. Around 20 April 2020, he further noticed excessive weight loss. In the meantime, both parents started to recover from their complaints. As they were suspected of having COVID-19, both parents and their two sons underwent a SARS-CoV-2 antibody test on 29 April 2020, which was positive (IgG⁺, IgM^–) for both parents and the patient. The dizygotic sibling of the patient tested negative for SARS-CoV-2 antibodies and experienced neither COVID-19- nor diabetes-related symptoms. On 5 May 2020 the patient presented at our local emergency ward because his symptoms relating to diabetes mellitus had worsened. He was then diagnosed with insulin-dependent diabetes mellitus and received treatment according to international guidelines. Based on the information presented in this figure (adapted from reports on the patient and his parents, and from antibody test results), we assume that the possible infection period of the patient can be narrowed down to the last 2 weeks of March 2020 (yellow bar) while it is unlikely that the patient had COVID-19 in April 2020 (red bar). This is further supported by the absence of IgM antibodies detected in the patient’s SARS-CoV-2 antibody test, which have previously been shown to persist for up to 4 weeks after infection with SARS-CoV-2 (ref. ¹⁵).