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


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 childrenmultisystem inflammatory syndrome in adultspostacute COVID-19 syndromecommunity-acquired pneumonia

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 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.

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.

In the analysis of more than 1000 adult patients admitted to the hospital with laboratory-confirmed COVID-19 infection in China, chest CT image abnormalities were detected in 86.2% of patients on admission. The most common abnormalities were ground glass opacity (56.4%) and bilateral patchy shadowing (51.8%). Additional imaging details are below.

Most patients (91.1%) received a diagnosis of pneumonia. Other complications included acute respiratory distress syndrome (ARDS) (3.4%) and shock (1.1%). Per the CDC, the median time to ARDS in patients with severe illness is 8-12 days. Uncommon complications were acute kidney injury, acute cardiac injury (cardiomyopathy, myocarditis), secondary infection, and rhabdomyolysisAplastic anemia rarely has been associated with COVID-19. Early studies suggest an association of pulmonary angiogenesis with COVID-19.


  • multisystem inflammatory syndrome potentially linked to COVID-19 has been reported in children and young adults; clinical features include Kawasaki-like and toxic shock syndrome-like presentations.
  • Little is known about primary COVID-19 infection in children at present. It seems to most commonly manifest as a mild respiratory illness or be asymptomatic. Severe primary COVID-19 illness in children has been uncommonly reported. In a multicenter cross-sectional study of 48 children admitted to US and Canadian pediatric intensive care units for COVID-19, over 80% had significant preexisting comorbidities. Early hospital outcomes were better in children than adults.

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, a unique subgroup of COVID-19 patients with low severity disease present with primarily digestive symptoms. In one study, up to 23% of patients with COVID-19 confirmed by polymerase chain reaction (PCR) testing presented with digestive symptoms (diarrhea, nausea, and vomiting and/or abdominal pain) alone. Up to 30% of patients with standard COVID-19 illness marked primarily by respiratory symptoms will have concurrent gastrointestinal symptoms including diarrhea, nausea, and vomiting and/or abdominal pain. In those 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. In one study, only 3% of patients had only gastrointestinal symptoms. 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. In one study, 71% of nonsurvivors from COVID-19 infection met DIC criteria compared with only 0.4% of survivors. Marked D-dimer elevation (3- to 4-fold elevation) at admission as well as elevation over time were also associated with high mortality. Despite this, therapeutic anticoagulation is not indicated in the absence of documented venous thromboembolism or atrial fibrillation. The efficacy of therapeutic anticoagulation remains controversial. An August 2021 study reported no clinical benefit in critically ill COVID-19 patients treated with therapeutic anticoagulation compared with those receiving prophylactic dosing. However, a second study of moderately ill patients with COVID-19 (non-intensive care unit [non-ICU]) purported a survival benefit with treatment dose anticoagulation compared with prophylactic dosing, although it also noted an increased significant bleed risk with the intervention. Close review of these two studies, however, raises concerns regarding findings given that a significant number of patients in both treatment arms did not receive treatment dose anticoagulation, whereas significant numbers in the prophylactic arms received intermediate dosing as opposed to standard prophylactic dosing. This, in addition to the lack of a clearly defined mechanistic explanation for the purported benefit in one population and not the other, has left the use of treatment dose anticoagulation for COVID-19 still in question. 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 venous thromboembolism (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.

Skin and oral mucosal manifestations of COVID-19 (not a common finding):

Several main mucocutaneous manifestations of COVID-19 have been described:

  • Pernio-like lesions on the acral surfaces (also known as “COVID toes,” pseudo-chilblains, and acute acro-ischemia), including erythema, edema, vesiculation, and purpura of the toes, fingers, feet, and hands. Lesions may be painful, itchy, or asymptomatic. Feet have been noted to be affected more frequently than hands. These manifestations occurred in younger individuals late in disease course and usually followed a milder illness. PCR is often negative in these patients, and the timing of onset has been touted as one explanation. Viral particles have been demonstrated within endothelial cells of affected areas, supporting that this cutaneous finding is a direct effect of the virus as opposed to quarantine-induced lifestyle changes, such as inactivity and ongoing cold exposure in unheated homes. However, some debate remains on this subject; it is possible that some individuals have chilblain-like lesions as a result of infection with SARS-CoV-2 and some have true chilblains as a result of lifestyle changes in the setting of a global pandemic.
  • A vesicular eruption with lesions all in the same stage (as opposed to chickenpox). In some cases, vesicles coalesce and become hemorrhagic. This manifestation occurred predominantly in middle-aged patients with moderate disease severity and lasted around 10 days. Itch was a common associated symptom.
  • An urticarial eruption.
  • A macular or papulosquamous eruption. Also classed in this group are cases with a perifollicular distribution, some that are erythema multiforme-like, some that are pityriasiform, and some that manifest secondary purpura as well. For both the urticarial and maculopapular eruptions, itch is frequent, and patients tend to present with more severe disease. In the largest study of skin manifestations of COVID-19, rash was present at the onset of other symptoms and lasted about 6-8 days.
  • Livedo or retiform purpura. Transient livedo has been seen in milder illness, but livedo racemosa or retiform purpura that may be complicated by skin necrosis may be seen in individuals with severe disease. A series of 4 such cases with these skin findings manifested evidence of a thrombotic state, including high D-dimer levels and suspected pulmonary emboli. Purpuric pressure ulcers have also been reported in hospitalized patients. Risk factors included obesity, impaired mobility due to critical illness, incontinence and malnutrition, and their presence seems to be independent of thrombotic vasculopathy.
  • Oral cavity findings may include lingual papillitis, glossitis, aphthous stomatitis, and mucositis. Dysgeusia and burning may accompany these findings. Macular and petechial enanthems of the palate have been reported in a minority of patients. A single case of herpes simplex virus-like vesicles on and around the lips has been reported.

Other less frequent findings included a purpuric flexural exanthem and an enanthem. Rare cases resembling leukocytoclastic vasculitis have been observed. There has been a case of unilateral laterothoracic exanthem linked to COVID-19. Reported COVID-19-induced nail changes include the “red half-moon nail sign,” where a red border to the lunula is seen in active disease. Beau lines and onychomadesis have been reported after resolution of COVID-19, and a greenish fluorescence of the proximal nails has been reported over favipiravir therapy. Periungual desquamation is seen in MIS-C.

A study reporting data from an international registry of individuals with confirmed COVID-19 found that the most commonly associated dermatologic finding was a morbilliform eruption. Pernio-like lesions were the second most common and were generally associated with mild disease. The least common skin finding in patients with COVID-19 was livedo reticularis; this was seen only in patients with severe COVID-19.

As more is learned about the long-term effects of COVID-19 in some individuals (post-acute sequelae of SARS-CoV-2 [PASC], so-called “long-haulers”), durable cutaneous manifestations have been observed. While morbilliform and urticarial eruptions were found to resolve within days, one study of an international registry found that 6.8% of those with chilblain-like lesions have persistence greater than 60 days. Papulosquamous eruptions of COVID-19 have generally been reported to resolve within a few weeks, but a case of a patient with such an eruption for 70 days has been reported in an international registry.

Impact of skin color on clinical presentation: Erythema is more readily appreciated in lighter skin colors. In darker skin colors, a deep red, maroon, or violaceous hue may be seen. In lighter skin colors, purpura may appear bright red, deep red, maroon, or violaceous. Purpura in darker skin colors will appear deep red, maroon, violaceous, or deep brown.


  • A review article highlighting the role of chest CT in early detection and management of COVID-19 reports that 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.

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