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This chapter addresses the novel Coronavirus disease (COVID-19) during the pandemic. The authors share their clinical experiences diagnosing and treating hundreds of patients and their interpretations of the frequently updated literature. The chapter summarizes currently available data on epidemiology, pathophysiology, clinical features, emerging variants, diagnosis, infection control, treatment, anticoagulation, prognosis, and the recent vaccinations.


As of this writing, more than 111 million confirmed cases of COVID-19 and 2.4 million related deaths have been reported globally. Since the first reports at the end of 2019 from Wuhan in the Hubei Province of China, cases have been reported in all continents, including Antarctica which reported its first case in December 2020.1

Epidemiologic investigation in Wuhan at the beginning of the outbreak identified an initial association with a seafood market that sold live animals, where most patients had worked or visited; the market was subsequently closed for disinfection.2 However, as the outbreak progressed, person-to-person spread became the main mode of transmission for the SARS-CoV-2 virus3 (Figure 20-1). Transmission from asymptomatic individuals (or individuals within the incubation period) also is well documented.4,5 However, detectable viral RNA does not always correlate with isolation of infectious virus; there may be a viral RNA threshold below which infectivity is unlikely.

Figure 20-1

Electronic microscopic image of SARS-CoV-2. (Courtesy of the CDC.

The risk of transmission after contact with an individual with COVID-19 increases with the closeness and duration of contact and appears highest with prolonged contact in indoor settings.6 Nevertheless, clusters of cases are frequently reported following family, work, or social gatherings where close personal contact can occur.

The virus can affect people of all ages. However, children and younger adults often remain asymptomatic or contract a mild form of the disease. Adults of advanced age are more susceptible to moderate, severe, or even critical illness.

Primary conditions that are considered risk factors for developing severe COVID-19 disease include:

  • hypertension

  • cardiac conditions (congestive heart failure/coronary artery disease or cardiomyopathies)

  • obesity (BMI = 30–40) and severe obesity (BMI > 40)

  • diabetes mellitus Type 2

  • immunocompromised state from a solid organ or bone marrow transplant or immunosuppressants for other chronic conditions

  • chronic lung disease

  • cancer

  • chronic kidney disease

  • sickle cell disease

  • smoking status; the relationship between smoking per se and the severity of COVID-19 is unclear; however, patients with underlying smoking-related COPD are at high risk of superimposed respiratory failure from COVID-19.

  • Uncontrolled HIV also may be a risk factor.


The host receptor for SARS-CoV-2 cell entry is the angiotensin-converting enzyme 2 (ACE2).7 SARS-CoV-2 binds to ACE2 through the receptor-binding gene domain (RBD) of its spike protein. The S1 subunit of a coronavirus ...

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