Clinical Presentation

Clinical Presentation

Clinical considerations for care of children and adults with confirmed COVID-19

Updated Dec. 29, 2023
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What You Need to Know
  • The clinical presentation of COVID-19 ranges from asymptomatic to critical illness.
  • An infected person can transmit SARS-CoV-2, the virus that causes COVID-19, before the onset of symptoms. Symptoms can change over the course of illness and can progress in severity.
  • Uncommon presentations of COVID-19 can occur, might vary by the age of the patient, and are a challenge to recognize.
  • In adults, age is the strongest risk factor for severe COVID-19. The risk of severe COVID-19 increases with increasing age especially for persons over 65 years and with increasing number of certain underlying medical conditions.

Incubation Period

Data suggest that incubation periods may differ by SARS-CoV-2 variant. Meta-analyses of studies published in 2020 identified a pooled mean incubation period of 6.5 days from exposure to symptom onset.(1) A study conducted during high levels of Delta variant transmission reported an incubation period of 4.3 days,(2) and studies performed during high levels of Omicron variant transmission reported a median incubation period of 3–4 days.(3,4)


People with COVID-19 may be asymptomatic or may commonly experience one or more of the following symptoms (not a comprehensive list)(5):

  • Fever or chills
  • Cough
  • Shortness of breath or difficulty breathing
  • Fatigue
  • Myalgia (Muscle or body aches)
  • Headache
  • New loss of taste or smell
  • Sore throat
  • Congestion or runny nose
  • Nausea or vomiting
  • Diarrhea

The clinical presentation of COVID-19 ranges from asymptomatic to severe illness, and COVID-19 symptoms may change over the course of illness. COVID-19 symptoms can be difficult to differentiate from and can overlap with other viral respiratory illnesses such as influenza(flu) and respiratory syncytial virus (RSV). Because symptoms may progress quickly, close follow-up is needed, especially for:

  • older adults
  • people with disabilities
  • people with immunocompromising conditions, and
  • people with medical conditions that place them at greater risk for severe illness or death.

The NIH COVID-19 Treatment Guidelines group SARS-CoV-2 infection into five categories based on severity of illness:

  • Asymptomatic or pre-symptomatic infection: people who test positive for SARS-CoV-2 using a virologic test (i.e., a nucleic acid amplification test [NAAT] or an antigen test) but who have no symptoms that are consistent with COVID-19.
  • Mild illness: people who may have any of the various signs and symptoms of COVID-19 but who do not have shortness of breath, dyspnea, or abnormal chest imaging.
  • Moderate illness: people who have evidence of lower respiratory disease during clinical assessment or imaging and who have an oxygen saturation (SpO2) ≥94% on room air at sea level.
  • Severe illness: people who have oxygen saturation <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: people who have respiratory failure, septic shock, or multiple organ dysfunction.

Asymptomatic and presymptomatic presentation

Studies have documented SARS-CoV-2 infection in people who never develop symptoms (asymptomatic presentation) and in people who are asymptomatic when tested but develop symptoms later (presymptomatic presentation).(6,7) It is unclear what percentage of people who initially appear asymptomatic progress to clinical disease.  Multiple publications have reported cases of people with abnormalities on chest imaging that are consistent with COVID-19 very early in the course of illness, even before the onset of symptoms or a positive COVID-19 test.(9)

Radiographic Considerations and Findings

Chest radiographs of patients with severe COVID-19 may demonstrate bilateral air-space consolidation.(23) Chest computed tomography (CT) images from patients with COVID-19 may demonstrate bilateral, peripheral ground glass opacities and consolidation.(24,25) Less common CT findings can include intra- or interlobular septal thickening with ground glass opacities (hazy opacity) or focal and rounded areas of ground glass opacity surrounded by a ring or arc of denser consolidation (reverse halo sign).(24)

Multiple studies suggest that abnormalities on CT or chest radiograph may be present in people who are asymptomatic, pre-symptomatic, or before RT-PCR detection of SARS-CoV-2 RNA in nasopharyngeal specimens.(25)

Common COVID-19 symptoms

Fever, cough, shortness of breath, fatigue, headache, and myalgia are among the most commonly reported symptoms in people with COVID-19.(5) Some people with COVID-19 have gastrointestinal symptoms such as nausea, vomiting, or diarrhea, sometimes prior to having fever or lower respiratory tract signs and symptoms.(10) Loss of smell and taste can occur, although these symptoms are reported to be less common since Omicron began circulating, as compared to earlier during the COVID-19 pandemic.(11,19-21)People can experience SARS-CoV-2 infection (asymptomatic or symptomatic), even if they are up to date with their COVID-19 vaccines or were previously infected.(8)

Several studies have reported ocular symptoms associated with SARS-CoV-2 infection, including redness, tearing, dry eye or foreign body sensation, discharge or increased secretions, and eye itching or pain.(13)

A wide range of dermatologic manifestations have been associated with COVID-19; timing of skin manifestations in relation to other COVID-19 symptoms and signs is variable.(14)Some skin manifestations may be associated with increased disease severity.(15)Images of cutaneous findings in COVID-19 are available from the American Academy of Dermatology.

Uncommon COVID-19 symptoms

Less common presentations of COVID-19 can occur. Older adults may present with different symptoms than children and younger adults. Some older adults can experience SARS-CoV-2 infection accompanied by delirium, falls, reduced mobility or generalized weakness, and glycemic changes.(12)


People infected with SARS-CoV-2 can transmit the virus even if they are asymptomatic or presymptomatic.(16) Peak transmissibility appears to occur early during the infectious period (prior to symptom onset until a few days after), but infected persons can shed infectious virus up to 10 days following infection.(22) Both vaccinated and unvaccinated people can transmit SARS-CoV-2.(17,18) Clinicians should consider encouraging all people to take the following prevention actions to limit SARS-CoV-2 transmission:

Clinicians should also recommend that people who are infected with SARS-CoV-2, follow CDC guidelines for isolation.

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