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COVID-19 in Adult
Other Resources UpToDate PubMed

COVID-19 in Adult

Contributors: Paritosh Prasad MD, Eric Ingerowski MD, FAAP, David Peritz MD, Jeffrey M. Cohen MD, Susan Burgin MD
Other Resources UpToDate PubMed


Refer to the US Centers for Disease Control and Prevention (CDC) (Information for Healthcare Professionals) for the most current information.

Coronavirus disease 2019 (COVID-19), previously known as 2019 novel coronavirus (2019-nCoV), is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

Clinical features:

Clinical features primarily include fever and upper respiratory tract symptoms with rhinorrhea, congestion, and pharyngitis that can progress to include symptoms of lower respiratory tract illness (eg, cough, shortness of breath), although many patients also report associated gastrointestinal complaints (nausea, vomiting). Reported cases have ranged from asymptomatic to severe; the case fatality rate has varied worldwide, ranging from 0.1%-18.1% based on data compiled by Johns Hopkins. Clinical presentation can vary significantly, particularly with respect to vaccination and boosting status and time from last COVID infection.

Illness can range from mild to critical:
  • Mild to moderate (mild symptoms up to mild pneumonia)
  • Severe (dyspnea, hypoxia, or > 50% lung involvement on imaging)
  • Critical (respiratory failure, shock, or multiorgan system dysfunction)

SARS-CoV-2 spreads from person to person easily. The incubation period is estimated to be between 2 and 14 days after exposure, with an estimated median incubation period of about 3-5 days. This incubation period appears to vary slightly with respect to different variants.
  • The virus is transmitted primarily via infectious secretions (respiratory droplets and sputum) between individuals in close contact (within 6 feet).
  • Airborne transmission can occur, particularly within enclosed spaces (even those with adequate ventilation) or under circumstances where the infectious individual is breathing heavily, such as while exercising or singing.
  • Transmission of SARS-CoV-2 from asymptomatic or presymptomatic persons can occur.
  • It is not yet known whether the virus can be transmitted by blood, vomit, urine, breast milk, or semen.

Multiple variants of the virus have circulated globally, including in the United States, and new variants are expected to occur. Omicron continues to be the dominant variant in the United States, with EG.5 becoming a dominant strain as of early August 2023. Other subvariants have included XBB.1.5, XBB.1.16, XBB.1.9.1, and XBB1.9.2. Subvariants may be less sensitive to neutralizing antibodies from prior COVID-19 vaccines and prior COVID infections and cause higher rates of reinfection.


There are reports of individuals previously diagnosed with COVID-19 becoming reinfected. Unvaccinated individuals are thought to be at higher risk.

Breakthrough infection:

Vaccine breakthrough infections may occur in fully vaccinated individuals. However, individuals vaccinated with a primary series or a primary series plus a booster dose are much less likely to experience severe symptoms than unvaccinated people. The occurrence of breakthrough infections with SARS-CoV-2 appears to be correlated with neutralizing antibody titers during the peri-infection period. The BA.5 and BA.4 variants currently circulating appear to be responsible for increasing numbers of breakthrough and reinfection cases in the United States.

Infection prevention and control in health care settings:

The CDC has provided updated guidance (updated May 8, 2023) on infection prevention and control to reduce facility risk, isolate symptomatic patients as soon as possible, and protect health care personnel.

About COVID-19
Coronaviruses are a family of viruses, some of which cause infection in humans and in animals such as camels, cats, and bats. When animal coronaviruses evolve, on rare occasion they can become infectious to and spread between humans (a zoonotic infection) as has occurred with Middle East respiratory syndrome (MERS) and SARS. This animal-to-human spread has been postulated to have occurred with SARS-CoV-2 with subsequent person-to-person transmission.

Related topics: multisystem inflammatory syndrome in children, multisystem inflammatory syndrome in adults, post-COVID conditions


U07.1 – COVID-19

840539006 – Disease caused by 2019 novel coronavirus

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Differential Diagnosis & Pitfalls

The differential diagnosis includes other etiologies of lower respiratory tract infection (depending on season).

Note: Viral coinfections (eg, influenza) have been reported in patients with COVID-19; thus, diagnosis of an alternative respiratory virus does not exclude SARS-CoV-2 virus infection.

Data have demonstrated that the majority of patients presenting with COVID-19 do not have concurrent bacterial infection, although those with COVID-19 and prolonged hospitalization often develop complicating bacterial infection.

Viral infection:
Bacterial pneumonia, eg:
Atypical bacterial pneumonia, eg:
Fungal pneumonia:
Skin manifestations (based on a Spanish study of 375 patients):

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Last Reviewed:06/03/2023
Last Updated:08/13/2023
Copyright © 2023 VisualDx®. All rights reserved.
COVID-19 in Adult
Imaging Studies image of COVID-19 - imageId=9733688. Click to open in gallery.  caption: 'Multifocal areas of airspace disease predominantly involving the lower lobes, compatible with multifocal pneumonia. SARS-CoV-2+.'
Multifocal areas of airspace disease predominantly involving the lower lobes, compatible with multifocal pneumonia. SARS-CoV-2+.
Copyright © 2023 VisualDx®. All rights reserved.