Criteria

World Health Organization (WHO): COVID-19 disease severity classification[444]

Mild illness

  • Symptomatic patients meeting the case definition for COVID-19 without evidence of hypoxia or pneumonia.

Moderate disease

  • Adolescent or adult: clinical signs of pneumonia (i.e., fever, cough, dyspnea, fast breathing) but no signs of severe pneumonia, including blood oxygen saturation levels (SpO₂) ≥90% on room air.

  • Children: cough or difficulty breathing plus fast breathing and/or chest indrawing and no signs of severe pneumonia. Fast breathing is defined as:

    • <2 months of age: ≥60 breaths/minute

    • 2-11 months of age: ≥50 breaths/minute

    • 1-5 years of age: ≥40 breaths/minute

  • While the diagnosis can be made on clinical grounds, chest imaging may assist in diagnosis and identify or exclude pulmonary complications.

Severe disease

  • Adolescent or adult: clinical signs of pneumonia (i.e., fever, cough, dyspnea) plus one of the following:

    • Respiratory rate >30 breaths/minute

    • Severe respiratory distress

    • SpO₂ <90% on room air

  • Children: clinical signs of pneumonia (i.e., cough or difficulty in breathing plus fast breathing or chest wall indrawing) plus at least one of the following:

    • SpO₂ <90%

    • Very severe chest indrawing, grunting, central cyanosis, or presence of any other general danger sign (i.e., inability to breastfeed or drink, lethargy or unconsciousness, or convulsions)

  • While the diagnosis can be made on clinical grounds, chest imaging may assist in diagnosis and identify or exclude pulmonary complications.

Critical disease

  • Presence of acute respiratory distress syndrome (ARDS), sepsis, septic shock, acute thrombosis, or multisystem inflammatory syndrome in children.

World Health Organization (WHO): hospitalization risk for patients with nonsevere disease[406]

Several recommendations for people with nonsevere disease, specifically for the use of antiviral drugs (i.e., nirmatrelvir/ritonavir, molnupiravir, remdesivir), are stratified by the likelihood of hospital admission. The criteria for deciding whether a patient is at high, moderate, or low risk of hospitalization are detailed below.

  • High risk (6%) of hospitalization

    • Diagnosed immunodeficiency syndromes.

    • History of solid organ transplant and receiving immunosuppressants.

    • Autoimmune illness and receiving immunosuppressants.

  • Moderate risk (3%) of hospitalization

    • Age ≥65 years.

    • Obesity.

    • Diabetes and/or chronic cardiopulmonary disease.

    • Chronic kidney or liver disease.

    • Active cancer.

    • Disabilities.

    • Comorbidities of chronic disease.

  • Low risk (0.5%) of hospitalization

    • Not at moderate or high risk of hospitalization (most patients are low risk).

Infectious Diseases Society of America (IDSA): disease severity definitions[401]

Mild-to-moderate illness

  • Patients with a SpO₂ >94% not requiring supplemental oxygen.

Severe illness

  • Patients with SpO₂ ≤94% on room air, including patients on supplemental oxygen.

Critical illness

  • Patients on mechanical ventilation and extracorporeal mechanical oxygenation (ECMO).

  • Includes end-organ dysfunction as is seen in sepsis/septic shock. The most commonly reported form of end-organ dysfunction is acute respiratory distress syndrome (ARDS).

Case definitions

Various case definitions are available:

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