Coronavirus (COVID-19): What You Need to Know

Updated April 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).

On March 11, 2020, the WHO declared COVID-19 a global pandemic. There have been more than 129 million confirmed human infections and more than 2.8 million deaths worldwide as of April 2, 2021. In the United States alone, there are more than 30 million confirmed cases. For an up-to-date heat map of global cases, click here.

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 mild to severe; some cases have been fatal. Some individuals with infection can be relatively asymptomatic.

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 FDA has allowed emergency use for the Pfizer-BioNTech COVID-19 vaccine for individuals aged 16 years and older (the vaccination series is 2 doses given 3 weeks apart), the Moderna COVID-19 vaccine for individuals aged 18 years and older (the vaccination series is 2 doses given 1 month apart), and the Janssen COVID-19 vaccine (Johnson & Johnson) in individuals aged 18 years and older (single dose).

Eligibility criteria for vaccination are determined by each state and territory.

Preventive measures:

Share with patients CDC recommendations on How to Protect Yourself and Others.

  • Get a COVID-19 vaccine.
  • Wear a mask to protect yourself and others and stop the spread of COVID-19.
  • Stay at least 6 feet (about 2 arm lengths) from others who don’t live with you.
  • Avoid crowds and poorly ventilated spaces. The more people you are in contact with, the more likely you are to be exposed to COVID-19.

Multiple variants of the virus are circulating globally, including in the United States. Per the CDC, these variants (the “UK variant” [B.1.1.7], the “South African variant” [B.1.351], and the “Brazil variant” [P1]) seem to spread more easily and quickly.


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.

What to look for:

Information to define the spectrum of clinical illness attributed to COVID-19 is still being gathered.

Emergency warning signs for COVID-19 include trouble breathing, persistent pain or pressure in the chest, new confusion or inability to arouse, and bluish lips or face.

Signs and symptoms of illness vary, and some people with COVID-19 infection can be relatively asymptomatic. Most patients, however, will experience one or more of the following over the course of disease:

  • Fever or chills
  • Cough
  • Dyspnea
  • Fatigue
  • Myalgias
  • Headache
  • New-onset anosmia or ageusia
  • Sore throat
  • Congestion or rhinorrhea
  • Nausea or vomiting
  • Diarrhea

Other signs and symptoms include anorexia, sputum production, repeated shaking with chills, arthralgia, sore throat, confusion, and hemoptysis. More severe disease has caused in some patients neurologic manifestations such as microembolic stroke, encephalopathy, agitation, delirium, and corticospinal tract signs. See below for further discussion of variant presentations.

What else could it be:

The differential diagnosis of COVID-19 includes other etiologies of lower respiratory tract infection.

Viral infection:

Bacterial pneumonia, eg:

Bacterial pneumonia, eg:

Atypical bacterial pneumonia, eg:

 Management of COVID-19 depends on the severity of illness.

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