Pictures of COVID-19 and disease information have been excerpted from VisualDx clinical decision support system as a public health service. Additional information, including symptoms, diagnostic pearls, differential diagnosis, best tests, and management pearls, is available in VisualDx.

Full Clinical Write-up

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 varies worldwide, ranging from 0.1%-4.9% 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 determined 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 HV.1 the dominant strain as of November 2023. Other circulating subvariants include EG.5, FL.1.5.1, XBB.1.16.6, and XBB.1.16.11 among others. Subvariants may be less sensitive to neutralizing antibodies from prior COVID-19 vaccines and prior COVID infections and cause higher rates of reinfection.


Individuals previously diagnosed with COVID-19 may become infected again due to waning immunity from prior infection and/or waning vaccine effectiveness that occurs over time.

Breakthrough infection:

Breakthrough infections may occur in individuals who are up to date with COVID-19 vaccinations. However, vaccinated individuals are much less likely to experience severe symptoms than unvaccinated people.

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 occasions 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 adultsmultisystem inflammatory syndrome in childrenpost-COVID conditionsskin and oral mucosal manifestations of COVID-19

A differential display for COVID-19

A differential display for COVID-19

A differential display for COVID-19

A differential display for COVID-19

A differential display for COVID-19

A differential display for COVID-19

A differential display for COVID-19

Look For:

Emergency warning signs for severe 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
  • Sore throat
  • Congestion or rhinorrhea
  • Myalgias
  • Headache
  • Nausea or vomiting
  • Diarrhea
  • Cough
  • Dyspnea
  • Fatigue
  • New-onset anosmia or ageusia

Children and infants may additionally present with ocular manifestations such as conjunctival secretions, conjunctival congestion, ocular pruritus, and eye rubbing (ie, viral conjunctivitis).

Skin and oral mucosal manifestations have been reported with COVID-19 (as well as multisystem inflammatory syndrome in children and adults and post-COVID conditions).

Other signs and symptoms include anorexia, sputum production, repeated shaking with chills, arthralgia, 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.

Lymphopenia, neutrophilia, elevated serum alanine aminotransferase and aspartate aminotransferase levels, elevated lactate dehydrogenase, high C-reactive protein, and high ferritin levels may be associated with greater illness severity. Some patients rapidly deteriorate 1 week after illness onset.

Most patients admitted to the hospital with laboratory-confirmed COVID-19 infection receive a diagnosis of pneumonia. The most common CT abnormality detected in COVID-19 pneumonia is ground glass opacity. Distribution of CT abnormalities is typically peripheral, and linear consolidations may be observed on CT several days after disease onset.

Other complications included acute respiratory distress syndrome (ARDS) and shock. Uncommon complications include acute kidney injury, acute cardiac injury (cardiomyopathy, myocarditis), secondary infection, and rhabdomyolysisAplastic anemia rarely has been associated with COVID-19.

A retrospective observational study reported that individuals with COVID-19 who were older than 40 years, men, Black adults, or with preexisting conditions had an elevated risk of developing new-onset persistent high blood pressure.

Diagnosis of COVID-19 in children and adults may be associated with an increased risk of subsequent new diagnosis of diabetes, including type 1 and type 2 diabetes.


  • multisystem inflammatory syndrome (MIS-C) potentially linked to COVID-19 has been reported in children and young adults; clinical features include Kawasaki-like and toxic shock syndrome-like presentations.
  • Primary COVID-19 infection in children seems to most commonly manifest as a mild respiratory illness or be asymptomatic. Severe primary COVID-19 illness in children has been uncommonly reported; children with significant preexisting comorbidities are at higher risk.

Gastrointestinal symptoms of COVID-19:

While the majority of symptomatic COVID-19 patients present with respiratory symptoms of cough, shortness of breath, and sore throat, some patients may concurrently present with digestive symptoms (diarrhea, nausea, and vomiting and/or abdominal pain); a subset of patients may present with only digestive symptoms.

In patients with diarrhea, symptoms can last for 1-14 days (5 days on average). In some cases, digestive symptoms such as diarrhea can be the initial presenting symptoms of COVID-19 in patients who may later develop respiratory symptoms or fever. Patients with digestive symptoms appear to have a longer duration between symptom onset and viral clearance and are more likely to have fecal samples positive for SARS-CoV-2 compared with those with respiratory symptoms.

COVID-19-associated coagulopathy:

COVID-19-associated coagulopathy is primarily characterized by elevations in fibrinogen and D-dimer levels. These elevations are generally in parallel with elevations in inflammatory markers such as C-reactive protein. Other markers of coagulation such as prothrombin time (PT) and partial thromboplastin time (PTT) are not generally elevated, and platelet counts are only mildly low (100 000 range), unlike standard sepsis-associated disseminated intravascular coagulation (DIC). Some COVID-19 patients can progress to a more fulminant DIC picture with severe tissue damage.

Development of DIC in COVID-19 is an extremely concerning finding, as it is associated with extremely poor prognosis. While there is controversy around the efficacy of therapeutic anticoagulation in the absence of documented venous thromboembolism (VTE) or atrial fibrillation, the growing consensus is that COVID-19 patients with moderate illness who are hospitalized but not in the intensive care unit (ICU) and have an elevated D-dimer (? twice the upper limits of normal) will benefit from therapeutic anticoagulation. At least a prophylactic dose of low molecular weight heparin (LMWH) is recommended for all hospitalized patients with COVID-19. Despite the development of coagulopathy, COVID-19 infection is only rarely complicated by bleeding.

COVID-19-associated cytokine release syndrome:

In addition to the bilateral diffuse alveolar injury that marks severe cases of COVID-19, these cases demonstrate a sustained decrease in lymphocytes compared with more mild cases as well as increased levels of inflammatory cytokines such as interleukin (IL)-6, IL-10, IL-2, and interferon (IFN)-?. This “cytokine storm” results in the development of cytokine release syndrome (CRS), which is characterized by a marked increase in vascular permeability with the development of severe vasoplegia and systemic hypotension, noncardiogenic pulmonary edema, and persistent fevers.

Acute COVID-19-associated cardiovascular complications:

Emerging evidence suggests that, like other viruses, COVID-19 can affect the heart, sometimes severely. This is more frequently seen in hospitalized patients, but increasing evidence raises the concern that even those who are not hospitalized with serious COVID-19 illness can experience cardiac injury. Cardiovascular effects can include but are not limited to arrhythmia, myocarditis, acute coronary syndrome, and cardiomyopathy.

In a retrospective cohort of > 1000 patients diagnosed with COVID-19, major arterial or VTE events, major adverse cardiovascular events, and symptomatic VTE were common in hospitalized patients despite high use of thromboprophylaxis. Patients in ICUs were most affected, although hospitalized non-ICU patients were also at risk. ARDS was strongly associated with increased risk.


  • Typical chest CT findings include multifocal bilateral ground glass opacities with patchy consolidations, peripheral subpleural distribution, and posterior part or lower lobe predilection. Less commonly, crazy-paving pattern or air bronchogram sign was observed. Pure consolidation, reversed halo sign, or pleural effusion was uncommonly detected.
  • Pure ground glass opacity lesions can be an early presentation of COVID-19 pneumonia.
  • Chest CT is superior to chest x-ray in early detection of COVID-19 pneumonia, but both have low specificity for the diagnosis.

The full text and image collection are available to VisualDx subscribers.

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