On January 21, 2020 (day 4 of illness), she did not complain of shortness of breath, but oxygen supplementation via nasal cannula (3 L/min) was started as a result of decreased arterial oxygen saturation around 91%. Her oxygen requirement increased to 6 L/min on January 24, 2020 (day 7 of illness), and chest radiography taken on January 25, 2020 (day 8 of illness) began to show chest infiltrates in the right lower lung field (Fig. 1F).