A 68-year-old Japanese woman who developed fatigue and fever (maximum: 38.8  C) was diagnosed with COVID-19. There had been an outbreak at her swimming club, which was the same club to which the patient in Case 1 belonged. She was diagnosed with mild disease without pneumonia upon arrival. She had two aggravation risk factors: age > 65 years and hypertension.
Her temperature was 37.1  C and SpO2 97 % upon admission. She was started on favipiravir (3600 mg on day 1, 1800 mg from day 2 onwards) and dexamethasone (6 mg on days 1-10). Her temperature was normal on the next day, and her fatigue gradually improved. On the morning of day 5, the nurse pointed out a change in her face color. There was no rash on her trunk, and a red color was localized in her face. She did not feel heat on her cheeks, had no other symptoms, and her SpO2 level was 99 %. Her vital signs were stable, and she did not complain of any other symptoms, so we simply observed her. A few hours later, her SpO2 suddenly dropped from 98 % to 94 %. Although she did not complain of any new symptoms, we performed CT. CT revealed a new lesion of pneumonia. She was switched from favipiravir to remdesivir (200 mg/day on day 1, 100 mg from day 2 onwards) and from dexamethasone to methylprednisolone (1000 mg/day on days 1-3, 125 mg/day on days 4-5). Her SpO2 dropped to 90 % at the lowest during the night, and she was started on oxygen. The next morning, she had recovered from the hypoxia (SpO2: 98 %), and oxygen was stopped. Her red face disappeared at that time. Her pneumonia had resolved and she was discharged 12 days later.