Table 1.

WHO guidelines for COVID-19 severity classification. Source: WHO (2020)

Category	Symptoms
Mild	Fever, cough, fatigue, such as sore throat, nasal congestion, headache
Moderate	Adolescent or adult with clinical signs of pneumonia (fever, cough, dyspnea, fast breathing) but no signs of severe pneumonia, including SpO2 ≥ 90% on room air, loss of smell, loss of taste, diarrhea, nausea and vomiting, myalgia
Severe	Adolescent or adult with clinical signs of pneumonia (fever, cough, dyspnea, fast breathing) plus one of the following: respiratory rate > 30 breaths/min; severe respiratory distress; or SpO2 < 90% on room air. Loss of smell, loss of taste, diarrhea, nausea and vomiting, myalgia
Critical	Chest imaging: (radiograph, CT scan, or lung ultrasound) bilateral opacities, not fully explained by volume overload, lobar or lung collapse, or nodules Mild ARDS (invasively ventilated): 4 ≤ OI < 8 or 5 ≤ OSI < 7.5 Moderate ARDS (invasively ventilated): 8 ≤ OI < 16 or 7.5 ≤ OSI < 12.3 Severe ARDS (invasively ventilated): OI ≥ 16 or OSI ≥ 12.3

ARDS Acute respiratory disease syndrome, CT Computerized tomography, OSI Oxygen Saturation Index, OI Oxygenation Index