COVID-19: Category Definitions, Symptoms and Those at Increased Risk

NOTE: Information and guidelines may change rapidly. Check in with listed references in ‘Learn More – Primary Sources’ to best keep up to date. This summary has been updated with the latest CDC guidelines on when to end quarantine.

SUMMARY:

The novel coronavirus, named SARS-CoV-2, is the pathogen underlying the pandemic (a global outbreak of disease). The disease associated with this virus has been officially named COVID-19. Coronaviruses represent a large family of viruses. They can cause human illness, but many are found in animals and, rarely, animal coronaviruses can evolve and infect people as was the case in previous infectious outbreaks such as MERS and SARS.

COVID-19 Categories
Symptoms
Those at Risk

COVID-19 Categories (NIH Panel)

Asymptomatic or pre-symptomatic infection
- Test positive for SARS-CoV-2 using a virologic test (i.e., a nucleic acid amplification test [NAAT] or an antigen test)
- No symptoms that are consistent with COVID-19
Mild illness
- Have any of the various signs and symptoms of COVID-19 (e.g., fever, cough, sore throat, malaise, headache, muscle pain, nausea, vomiting, diarrhea, loss of taste and smell)
- No shortness of breath, dyspnea, or abnormal chest imaging
Moderate illness
- Evidence of lower respiratory disease during clinical assessment or imaging and oxygen saturation (SpO₂) ≥94% on room air at sea level
Severe illness
- SpO₂ <94% on room air at sea level, a ratio of arterial partial pressure of oxygen to fraction of inspired oxygen (PaO₂/FiO₂) <300 mm Hg, a respiratory rate >30 breaths/min, or lung infiltrates >50%
Critical illness
- Respiratory failure, septic shock, and/or multiple organ dysfunction

Note: SpO2 is a key parameter for defining the illness categories listed above | Pulse oximetry has important limitations (e.g., skin pigmentation, thickness or temperature) | Clinicians who use SpO2 when assessing a patient must be aware of those limitations and conduct the assessment in the context of that patient’s clinical status

Pregnancy: Oxygen supplementation in pregnancy generally used when SpO₂ <95% on room air at sea level to accommodate the physiologic needs of mother and fetus

Symptoms

Incubation period
- Time from exposure to development of symptoms: 2 to 14 days
  - Delta variant studies: Mean incubation period of 4.3 days (see ‘Learn More – Primary Sources Below) which was shorter than initial variants (5.0 days)
  - Omicron variant studies: Median incubation period of 3 to 4 days

Signs and Symptoms
- Fever or chills
- Cough
- Shortness of breath or difficulty breathing
- Fatigue
- Muscle or body aches
- Headache
- New loss of taste or smell
- Sore throat
- Congestion or runny nose
- Nausea or vomiting
- Diarrhea
Additional points regarding presentation
- Older adults: Especially those with comorbidities may have delayed presentation of fever and respiratory symptoms
- Fatigue, headache, and muscle aches (myalgia) are among the most commonly reported symptoms in people who are not hospitalized
- Sore throat and nasal congestion or runny nose (rhinorrhea) also may be prominent symptoms
- GI symptoms may be relatively common
  - Nausea, vomiting or diarrhea may occur prior to fever and lower respiratory tract signs and symptoms
- Loss of smell (anosmia) or taste (ageusia) has been commonly reported, especially among women and younger or middle-aged patients

Those at Risk Based on Evidence (CDC)

Age
- The CDC states

Age is the strongest risk factor for severe COVID-19 outcomes. Approximately 54.1 million people aged 65 years or older reside in the United States; in 2020 this age group accounted for 81% of U.S. COVID-19 related deaths, and as of September 2021 the mortality rate in this group was more than 80 times the rate of those aged 18-29

Higher Risk: Meta-analysis or systematic review demonstrates good or strong evidence

Asthma
Cancer
Cerebrovascular disease
Chronic kidney disease*
Chronic lung diseases limited to
- Interstitial lung disease
- Pulmonary embolism
- Pulmonary hypertension
- Bronchiectasis
- COPD (chronic obstructive pulmonary disease)
Chronic liver diseases limited to
- Cirrhosis
- Non-alcoholic fatty liver disease
- Alcoholic liver disease
- Autoimmune hepatitis
Cystic fibrosis
Diabetes mellitus, type 1 and type 2*‡
Disabilities‡
- Attention-Deficit/Hyperactivity Disorder (ADHD)
- Cerebral Palsy
- Congenital Malformations (Birth Defects)
- Limitations with self-care or activities of daily living
- Intellectual and Developmental Disabilities
- Learning Disabilities
- Spinal Cord Injuries
Heart conditions (such as heart failure, coronary artery disease, or cardiomyopathies)
HIV (human immunodeficiency virus)
Mental health disorders limited to
- Mood disorders, including depression
- Schizophrenia spectrum disorders
Neurologic conditions limited to dementia‡
Obesity (BMI ≥30 kg/m² or ≥95th percentile in children)*‡
Primary Immunodeficiencies
Pregnancy and recent pregnancy
Physical inactivity
Smoking, current and former
Solid organ or hematopoietic cell transplantation
Tuberculosis
Use of corticosteroids or other immunosuppressive medications

Suggestive Higher Risk: Underlying medical condition or risk factor that neither has a published meta-analysis or systematic review nor completed the CDC systematic review process

Children with certain underlying conditions
Down syndrome
HIV (human immunodeficiency virus)
Neurologic conditions, including dementia
Overweight (BMI ≥25 kg/m2, but <30 kg/m2)
Sickle cell disease
Solid organ or blood stem cell transplantation
Substance use disorders
Use of corticosteroids or other immunosuppressive medications

Comorbidities with mostly case series, case reports, or, if other study design, the sample size is small

Overweight (BMI ≥25 kg/m², but <30 kg/m²)
Sickle cell disease
Substance use disorders
Thalassemia

Mixed Evidence: Meta-analysis or systematic review is inconclusive, either because the aggregated data on the association between an underlying condition and severe COVID-19 outcomes are inconsistent in direction or there are insufficient data