Any signs and symptoms (e.g., fever, cough, sore throat, malaise, headache, muscle pain) without shortness of breath, dyspnea, or abnormal chest imaging.
Moderate illness
Evidence of lower respiratory disease by clinical assessment or imaging and a saturation of oxygen (SaO2) > 93% on room air at sea level.
Severe illness
Respiratory frequency > 30 breaths per minute, SaO2 ≤ 93% on room air at sea level, ratio of arterial partial pressure of oxygen to fraction of inspired oxygen (PaO2/FiO2) < 300, or lung infiltrates > 50%.
Critical illness
Respiratory failure, septic shock, and/or multiple organ dysfunction.
