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Potentially life-threatening emergency
COVID-19 in Adult
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Potentially life-threatening emergency

COVID-19 in Adult

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


Updated December 1, 2021. 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 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 0.9%-7.6% based on data compiled by Johns Hopkins. There is some evidence that new variants of SARS-CoV-2 (eg, Delta) present with predominantly upper respiratory symptoms such as sore throat and nasal discharge, although the risk for progression to lower tract symptoms seems to be at least as frequent as with prior variants. 

An association exists between the risk of severe COVID-19 and a multigene locus at 3p21.31 and the ABG blood group locus at 9q34.2. Mutations in type I interferon pathway genes have been associated with severe disease.

Severity breakdown rates per the Chinese Center for Disease Control and Prevention:
  • Mild to moderate (mild symptoms up to mild pneumonia): 81%
  • Severe (dyspnea, hypoxia, or > 50% lung involvement on imaging): 14%
  • Critical (respiratory failure, shock, or multiorgan system dysfunction): 5%

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 4-5 days.
  • The virus is transmitted primarily via infectious secretions (respiratory droplets and sputum) between individuals in close contact (within 6 feet for a total of 15 minutes or more over a 24-hour period [including multiple short exposures]).
  • Transmission of SARS-CoV-2 from asymptomatic or presymptomatic persons can occur.
  • 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.
  • It is not yet known whether the virus can be transmitted by blood, vomit, urine, breast milk, or semen.

Multiple variants of the virus are circulating globally, including in the United States. Per the CDC, these variants (the Alpha variant [B.1.1.7], the Beta variant [B.1.351], the Gamma variant [P.1], the Delta variant [B.1.617.2], B.1.621, the Delta plus variant [AY lineages], and the Lambda variant [C.37]) all seem to spread more easily and quickly. As of July 2021, the Delta variant accounts for the majority of new COVID-19 cases in the United States. As of December 1, 2021, the Omicron variant [B.1.1.529] has been detected in the United States.


While uncommon, there are rare reports of individuals previously diagnosed with COVID-19 becoming reinfected. Individuals aged 65 or older are thought to be at higher risk. Moreover, it is possible for individuals diagnosed with one variant of the virus to be reinfected if they are exposed to a different strain. Whether reinfection rates will remain low in the setting of increasing variant transmission remains to be seen.

Breakthrough infection:

Breakthrough infections can occur in fully vaccinated individuals. Most reported cases have been mild or asymptomatic, although symptoms can persist for days to weeks. In a large study of vaccinated health care workers, the most commonly reported symptoms were upper respiratory congestion, myalgia, loss of smell or taste, and fever or rigors. About one-fifth of patients reported having "long-COVID" symptoms at 6 weeks after diagnosis. Additionally, the occurrence of breakthrough infections with SARS-CoV-2 appears to be correlated with neutralizing antibody titers during the peri-infection period.

Infection prevention and control in health care settings:

The CDC has provided updated guidance (updated September 10, 2021) 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 others 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, postacute COVID-19 syndrome, community-acquired pneumonia


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, dengue) have been reported in patients with COVID-19; thus, diagnosis of an alternative respiratory virus does not exclude SARS-CoV-2 virus infection. In addition, patients with COVID-19 have been reported presenting with concurrent community-acquired bacterial pneumonia.

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:10/14/2021
Last Updated:11/30/2021
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Potentially life-threatening emergency
COVID-19 in Adult
Copyright © 2022 VisualDx®. All rights reserved.