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  • Asymptomatic in approximately 20–35% of adults and most children.

  • When symptomatic, adults often have respiratory tract illness with fever and cough, upper tract symptoms being more prominent with the omicron variant.

  • Advanced pulmonary complications (pneumonia, acute respiratory distress syndrome [ARDS]) occur with fulminant disease.

  • Mortality of 1–21% (varied by geographic area and strain).

  • High predilection for the elderly, the immunocompromised, those with chronic diseases, those living in crowded conditions.

General Considerations

In late 2019, a novel coronavirus named “SARS-CoV-2” emerged. The illness caused by this virus is called “Coronavirus Disease 2019” or “COVID-19.” Coronaviruses are a large family of viruses commonly found in humans as well as many other species of animals, including bats, camels, cattle, and cats. There are four genera of coronaviruses, of which only the alphacoronaviruses (coronavirus NL63 and 229E) and the betacoronaviruses affect humans. Like SARS-CoV-1, MERS-CoV, and the human common cold coronaviruses HC43 and HKU1, the SARS-CoV-2 virus is a betacoronavirus. SARS-CoV-1 and MERS-CoV were identified 7 and 17 years, respectively, before SARS-CoV-2 was identified. All coronaviruses likely originated in bats. The spread of SARS-CoV-2 from bats was perhaps amplified by pangolins, an Asian anteater whose scales are traded on black markets for circulatory problems, although this theory remains under investigation. Antibodies to SARS-CoV-2 have been identified in bats over a 4800 km range in Asia as well as in pangolins at a wildlife checkpoint station in southern Thailand. A WHO investigative team was unable to implicate a specific area of Wuhan as the origin of the outbreak and further geo-epidemiologic studies are needed. It is thought unlikely that the virus escaped from a laboratory, and while the exact animal reservoir for SARS-CoV-2 is not identified, the largest body of evidence supports a zoonotic origin.

A potential role of mink is under study, with mink farms being a secondary and transmitting source of SARS-CoV-2 infections in the Netherlands; mink farms are recognized as potential sources of human infection in seven other European countries and the United States. Transmission to humans does not appear to regularly occur with cats and dogs, who are also secondarily infected by humans although a canine-feline recombinant coronavirus is reported from a Malaysian patient with pneumonia. The plasticity of coronavirus infections is confirmed by studies conducted by the University of Florida that show the development of porcine delta coronavirus infections among children in Haiti with acute febrile illness. In addition, an acute febrile illness seen in a medical team member in Haiti shows analogy to a Malaysian canine coronavirus. Thus, the complexity and interrelationship of human coronavirus infections and nonhuman reservoirs is in great need of further study.

A. Epidemiology

Early in the outbreak, most fatalities were from Wuhan and ...

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