**6.3 Thromboembolic complications**

Venous thromboembolism (VTE), including extensive deep vein thrombosis (DVT) and pulmonary embolism (PE), is common in severely ill patients with COVID-19, particularly among patients in the intensive care unit (ICU), among whom reported rates have ranged from 10 to 40 percent. Arterial thrombotic

events, including acute stroke (even in patients younger than 50 years of age without risk factors) and limb ischemia, have also been reported.

#### **6.4 Neurologic complications**

Encephalopathy is a common complication of COVID-19, particularly among critically ill patients; Stroke, movement disorders, motor and sensory deficits, ataxia, and seizures occur less frequently.

#### **6.5 Inflammatory complications**

Some patients with severe COVID-19 have laboratory evidence of an exuberant inflammatory response, with persistent fevers, elevated inflammatory markers (eg, D-dimer, ferritin), and elevated proinflammatory cytokines; these laboratory abnormalities have been associated with critical and fatal illnesses. Although these features had been likened to cytokine release syndrome (eg, in response to T cell immunotherapy), the levels of proinflammatory cytokines in COVID-19 are substantially lower than those seen with cytokine release syndrome as well as with sepsis. Other inflammatory complications and auto-antibody-mediated manifestations have been described.

Guillain-Barré syndrome may occur, with onset 5 to 10 days after initial symptoms. A multisystem inflammatory syndrome with clinical features similar to those of Kawasaki disease and toxic shock syndrome has also been described in children with COVID-19. In the rare adults in whom it has been reported, this syndrome has been characterized by markedly elevated inflammatory markers and multiorgan dysfunction (in particular cardiac dysfunction), but minimal pulmonary involvement.

#### **6.6 Secondary infections**

Secondary infections do not appear to be common complications of COVID-19 overall, the reported rate of bacterial or fungal coinfections was 8 percent; these included mainly respiratory infections and bacteremia. Several reports have described presumptive invasive aspergillosis among immunocompetent patients with ARDS from COVID-19, although the frequency of this complication is uncertain.

Autopsy studies have noted detectable SARS-CoV-2 RNA (and, in some cases, antigen) in the kidneys, liver, heart, brain, and blood in addition to respiratory tract specimens, suggesting that the virus disseminates systemically in some cases; whether direct viral cytopathic effects at these sites contribute to the complications observed is uncertain.

#### **7. Summary**

The clinical spectrum of severe acute respiratory syndrome coronavirus 2 (SARS-COV-2) infection ranges from asymptomatic infection to critical and fatal illness. The proportion of infections that are asymptomatic is uncertain, as the definition of "asymptomatic" varies across studies and longitudinal follow-up to identify those who ultimately develop symptoms is often not performed. Nevertheless, some estimates suggest that up to 40 percent of infections are asymptomatic.

Most symptomatic infections are mild. Severe disease (eg, with hypoxia and pneumonia) has been reported in 15 to 20 percent of symptomatic infections; it

#### *Clinical Characteristics of COVID-19 Infection DOI: http://dx.doi.org/10.5772/intechopen.99088*

can occur in otherwise healthy individuals of any age, but predominantly occurs in adults with advanced age or certain underlying medical comorbidities.

Cough, myalgias, and headache are the most commonly reported symptoms. Other features, including diarrhea, sore throat, and smell or taste abnormalities, are also well described. Pneumonia, with fever, cough, dyspnea, and infiltrates on chest imaging, is the most frequent serious manifestation of infection. There are no specific clinical features that can yet reliably distinguish COVID-19 from other viral respiratory infections.

Certain laboratory features, such as lymphopenia, elevated D-dimer, and elevated inflammatory markers have been associated with severe COVID-19.

Acute respiratory distress syndrome (ARDS) is the major complication in patients with severe disease and can manifest shortly after the onset of dyspnea. Other complications of severe illness include thromboembolic events, acute cardiac injury, kidney injury, and inflammatory complications.

The possibility of COVID-19 should be considered primarily in patients with compatible symptoms, in particular fever and/or respiratory tract symptoms, who reside in or have traveled to areas with community transmission or who have had recent close contact with a confirmed or suspected individual with COVID-19. All symptomatic patients with suspected SARS-CoV-2 infection should undergo testing.
