Table 1.

Definition of disease severity in patients with coronavirus disease 2019

	Mild	Moderate	Severe	Critical
WHO [9] (children/adolescents/adults	Nonsevere: absence of signs of severe or critical disease		SpO2 < 90% on room air	Requires life sustaining treatment
			Respiratory rate >30 in adults	Acute respiratory distress syndrome
			Raised respiratory rate in children*	Sepsis
			Signs of severe respiratory distress	Septic shock
IDSA [10] (adults)	Nonsevere: patients with SpO2 >94% not requiring supplemental oxygen		Patients with SpO2 ≤94% on room air, including patients on supplemental oxygen	Patients on mechanical ventilation and ECMO
				End organ dysfunction in sepsis/septic shock
North American Pediatric Infectious Diseases Experts Panel [5]	No new or increased supplemental oxygen requirement, with symptoms limited to the upper respiratory tract	No new or increased supplemental oxygen requirement, with symptoms involving the lower respiratory tract, or radiographic findings on chest x-ray	New or increase from baseline supplemental oxygen requirement without the need for new or increase in baseline noninvasive†/invasive mechanical ventilation	New or increased requirement for invasive or noninvasive mechanical ventilation, sepsis, or multiorgan failure
				Or rapidly worsening clinical trajectory that does not yet meet these criteria
Australia [1] (children/adolescents)	No supplemental oxygen required to maintain SpO2 >92%	Requires low-flow oxygen (nasal prongs or mask) to maintain SpO2 > 92%	Requires high-flow oxygen at 2 L/kg/min to maintain SpO2 > 92%	Hemodynamically unstable without inotropic or vasopressor support
				Other organ failure
				Requires advanced modes of support to maintain oxygenation: high-flow nasal oxygen at > 2 L/kg/min‡, or noninvasive ventilation, or intubation and

WHO, World Health Organization; IDSA, Infectious Diseases Society of America; SpO2, peripheral oxygen saturation; ECMO, extracorporeal membrane oxygenation.

^*Respiratory rate: <2 months, ≥ 60/min; 2–11 months, ≥50/min; 1–5 years, ≥40/min.

^†Noninvasive mechanical ventilation: high-flow nasal canula, continuous positive airway pressure, or bilevel airway pressure.

^‡Infants and neonates <4 kg may be managed on high-flow nasal cannula oxygen at 2–8 L/min irrespective of weight.