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

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

  • High predilection for older adults, patients who are immunocompromised, have chronic diseases, who live in crowded conditions.

General Considerations

Coronaviruses are a large family of viruses commonly found in humans and other species of animals, including bats, camels, cattle, cats, white-tailed deer, and hamsters. 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. All coronaviruses likely originated in bats.

A. Epidemiology

While SARS-CoV-2 antibodies have been identified in retrospective analysis of US blood donors as early as December 2019, the earliest known case in the United States was documented on January 21, 2020, in a man who had recently returned to the state of Washington from China.

Globally, SARS-CoV-2 has surpassed Mycobacterium tuberculosis as the leading single infectious agent cause of mortality. The mortality rate from COVID-19 is estimated to be 1–21% (varied by geographic area and strain). Determination of case tallies, however, is complicated by home testing and thus may grossly underestimate case counts in areas with high rates of home testing. Home testing is less common among Black persons, older adults, persons living in poverty, and those with less education. The actual number of deaths caused by COVID-19 may be up to 50% higher than reported. Significant increases in deaths attributable to diabetes and heart disease are recorded since the advent of the pandemic. Accordingly, the US CDC has identified “hotspot counties” where social vulnerability to COVID-19 is greater. Such counties show a higher proportion of racial and ethnic minorities, a greater density of housing units as well as more crowded housing (persons/room).

The average life expectancy for Americans is anticipated to be reduced by 1.13 years for 2020 with 2–3 times greater reduction in Black and Latino/Latina populations than in the White population. Underestimation of deaths from COVID-19 also is suggested in studies from India with the greater burden of the pandemic in disadvantaged communities. There appears to be a relatively low prevalence of the SARS-CoV-2 virus in populations of African countries. This is, in part, due to the relatively young age of African populations and the consequent paucity of older, vulnerable populations.

A case tally and other current information are available through the WHO website ( and, with an interactive map, through The Johns Hopkins University Coronavirus Resource Center website (


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