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Commentary—COVID-19: What we Know About Human Coronavirus Infections

27/2/2020 Matthew E. Levison, MD, Drexel University College of Medicine|Drexel University;

Coronaviruses, so-named because protein spikes on the surface of the virus resemble the sun’s corona, are common. Most cause respiratory, gastrointestinal, liver, and neurologic diseases in animals.

Human Coronavirus Infection (HCoV)

Only 7 coronaviruses cause disease in humans (HCoV).

Four of the 7 viruses cause mild and self-limiting upper respiratory tract infections, such as the common cold, but they can cause severe lower respiratory tract infections, including pneumonia, in infants, older people, and people whose immune systems are not working well. These HCoV infections show a seasonal pattern with most cases occurring in the winter months in temperate climate countries.

Three of the 7 HCoV (SARS-CoV, MERS-CoV, and SARS-CoV2) have caused major outbreaks of deadly pneumonia in the 21st century.


The first of these outbreaks, severe acute respiratory syndrome (SARS), first emerged in November 2002 in Guangdong province in southern China and caused an epidemic that spread within months to 29 countries and 6 continents. It sickened over 8,000 people and killed almost 800 worldwide. The majority of cases occurred in Mainland China and Hong Kong. In the United States, only 8 people had laboratory-confirmed SARS; all 8 had traveled to areas where SARS-CoV transmission was occurring.


The next HCoV to cause deadly infection was Middle East Respiratory Syndrome coronavirus (MERS-CoV), which emerged in the Arabian Peninsula in September 2012. MERS-CoV has caused recurrent outbreaks that have sickened over 2,500 people and about 1 in 3 infected people died. Most infected people lived in or recently traveled from the Arabian Peninsula. 85% of cases were reported in Saudi Arabia. The largest outbreak of MERS outside the Arabian Peninsula occurred in South Korea in 2015, associated with a traveler returning from the Arabian Peninsula.


The seventh HCoV to be discovered is SARS-CoV2, the cause of an outbreak, named COVID-19, that is currently spreading worldwide. The outbreak began in Wuhan in Central China. (Wuhan is home to the Wuhan Institute of Virology, a leading center for coronavirus research, although no connection is suspected between the research and the current outbreak.) The infection is believed to have originated in bats and to have made the jump to human beings at a seafood and live animal market in the city, through an infected animal that was being sold as exotic food at the market. Subsequent patients likely acquired the infection from other human cases. The incubation period was reported to be less than 14 days, supporting a 14-day quarantine period.

After 9 weeks of sustained transmission, as of February 25, Hubei Province reports 64,084 confirmed cases with 2,346 deaths. The actual number of cases is probably much higher as only the most severe cases are likely included in reports due to shortages of testing kits. The fatality rate so far seems lower than that of SARS and MERS but higher than that of epidemic influenza. The presence of many undiagnosed mild infections is probably limiting efforts to control further spread of this infection.

Chinese authorities responded by quarantining millions of people in Hubei Province on Jan 23, 2020. The restrictions came on the eve of Lunar New Year - one of the most important dates in the Chinese calendar, when millions of people travel home. In fact, it was estimated that five million people left Wuhan before the lockdown began and the number of cases correspondingly surged in the surrounding Chinese provinces and cases with a history of travel to or from Wuhan then began to appear outside China, in places such as Hong Kong and Singapore.

One British businessman contracted the SARS-CoV2 at a conference held in Singapore on Jan 20-22, 2020 and attended by 109 people from many different countries, at least one of whom was from Hubei, before traveling to France, where he spread the disease to 11 fellow guests at a ski chalet in the French Alps. He then flew home to the United Kingdom via Switzerland. During his travels across several countries, he would have come into contact with many people before discovering he harbored SARS-CoV2.

Transmission of SARS-CoV2

SARS Co-V2 is thought to be spread mainly by

  • Inhalation of respiratory droplets spread by a cough or sneeze of an infected person

Touching a contaminated surface and then touching your eyes or mouth may also spread the virus.

Could it be a pandemic?

A pandemic involves sustained transmission through multiple generations of the infectious agent in many countries on a global scale. Up until now, almost 98% of cases have occurred in China. Outside China, infections have involved mainly travelers who became infected in China. Sustained transmission of SARS-CoV2 outside China has occurred in only a few countries, but the pattern is clearly changing rapidly. 

A week ago, the indications of a COVID-19 epidemic occurring in the United States appeared to be low. But this is also changing very rapidly. Over 48 hours from Feb 21 to Feb 23 COVID-19 cases in the U.S. increased from 15 to 35, including 13 travel-associated cases, 18 cases among repatriated U.S. citizens from the Diamond Princess cruise ship quarantined in Japan and three cases in U.S. citizen evacuees from Wuhan. A resident of California, who had not traveled to countries in which the SARS-CoV2 virus is circulating and was not exposed to anyone known to be infected with the coronavirus, might be the first case in the United States of "community spread," the US Centers for Disease Control and Prevention said on Wednesday, Feb 26, 2020. It now brings the number of cases in this country to 60, including the 3 cases among Americans who were repatriated from Wuhan and 42 from the Diamond Princess cruise ship, plus 15 cases confirmed in this country.


There is as yet no vaccine that could prevent further spread of SARS-CoV2, and no specific antiviral drugs that could treat it. But researchers worldwide are moving quickly to test drugs. Many organizations, including the NIH, the Chinese Center for Disease Control and Prevention, the University of Hong Kong, the University of Queensland, the University of Saskatchewan, and pharmaceutical companies are working to develop possible vaccines against SARS-CoV-2. It is hoped that rapid vaccine and drug development can mitigate the evolution of COVID-19 into a pandemic.

The most effective methods of preventing infections are primarily those used for other infections:

  • Avoiding contact with people who are infected (in other words, people who are sick should stay at home)
  • Avoiding touching one’s eyes, nose, and mouth with unwashed hands
  • Washing hands often with soap and water for at least 20 seconds or using an alcohol-based hand sanitizer that contains at least 60% alcohol if soap and water are not available.

Surfaces that are touched by many people (eg, elevator buttons, doorknobs, bathroom fixtures) should be cleaned regularly with a disposable wipe.

Facemasks are probably not needed for most people. However, medical personnel and people who are caring for people with SARS CoV-2, should wear tight-fitting facemasks called N-95. Simple loose-fitting surgical masks do not really keep people from breathing infectious airborne droplets. However, surgical (not N-95) facemasks should be worn by people infected with COVID-19 when they are around others exposed to the infected wearer’s respiratory emissions. Because N-95 facemasks fit tightly to the face, their use may make a patient’s breathing difficult.

People who are very sick may need to be isolated in a hospital. People with less severe infection can be isolated at home. People who are well but have had contact with a person who is infected with COVID-19 should be quarantined at home for 14 days (the incubation period).