Clinical Presentation

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)

Presentation

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.

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⁾

Transmission

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:

• stay up to date with COVID-19 vaccines,
• test for COVID-19 when symptomatic or exposed to someone with COVID-19, as recommended by CDC,
• wear a high-quality mask when recommended,
• avoiding contact with individuals who have suspected or confirmed COVID-19,
• improving ventilation when possible,
• and follow basic health and hand hygiene guidance.

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

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