Patient Stratification
The clinical classifications were as follows: (1) non-severe ill patients: mild, with fever, respiratory tract symptoms, and imaging shows pneumonia, (2) severe ill patients: meet any of the following: a) respiratory distress, respiratory rate ≥ 30 beats/min, b) in the resting state, means oxygen saturation ≤ 93%, c) arterial blood oxygen partial pressure / oxygen concentration ≤ 300mmHg (1mmHg = 0.133kPa), d) respiratory failure occurs and requires mechanical ventilation, e) shock occurs.