Methods
This is a single-center retrospective observational study conducted at Atsugi City Hospital, Kanagawa, Japan. This study was approved by the ethics committee of this hospital (approval number: R2-07). Data among adult inpatients (≥20 years old) with COVID-19 treated with SPT from February 5 to May 31, 2020, were retrospectively reviewed. Throat or nasal swabs were taken for the reverse transcription polymerase chain reaction (RT-PCR) test. A diagnosis of COVID-19 was determined when both clinical symptoms and positive RT-PCR were observed. Day 1 was defined as the first onset of the symptoms.