Severe COVID-19 as a Possible Mediator of Autoimmunity and Sjögren's Syndrome.

We treated a 65-year-old man for COVID-19 who was hospitalized urgently due to life-threatening respiratory decompensation and later developed cardiac arrest, both of which were successfully treated. Three days prior to the patient's urgent hospitalization, he had a high fever of over 38.0°C. Viral infection was diagnosed by polymerase chain reaction (PCR) on the day of admission, which was negative on the 11th day. Blood analysis on the second day was strongly positive for COVID-19 IgG antibodies, which continued for one year. Because of the acute increase in viral IgG antibodies, we performed other immunological analyses; Sjögren's syndrome antigen A (SS-A) and Sjögren's syndrome antigen B (SS-B) antibodies were positive, although he had no history of autoimmune diseases. Subsequent salivary-gland biopsy and pathological analysis confirmed the diagnosis of Sjögren's syndrome. The severe clinical manifestations and early antibody seroconversion in this case suggest COVID-19 as a mediator of autoimmunity and Sjögren's syndrome.