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A newly identified virus that emerged late last year in the central Chinese city of Wuhan, causing an explosive outbreak of sometimes fatal pneumonia, has become a global health emergency. The culprit is a so-called coronavirus dubbed 2019-nCoV. It belongs to a family of viruses responsible for diseases that range in severity from the common cold to severe acute respiratory syndrome, or SARS, which killed almost 800 people in a 2002-2003 outbreak.

1. What makes this virus so bad?

It has been described as “insidious” because a large portion of infected people are well enough to go about their daily business, potentially spreading it to others. In two months, the number of confirmed cases and deaths surpassed those in the entire SARS epidemic. As of early February the apparent mortality rate was about 2%, lower than for SARS, but such numbers are unreliable in the early stages of an outbreak. Some disease modeling experts project there are likely anywhere from 75,000 to hundreds of thousands more actual infections, as accurate counts from overwhelmed areas -- especially Wuhan and the surrounding Hubei province -- are difficult to come by, partly due to a shortage of tests.

2. What’s a coronavirus?

Coronaviruses are named for their crown-like shape. There’s a large family of them. Some transmit easily from person to person, while others do not. The World Health Organization says that new strains emerge periodically around the globe, and several known versions are circulating in animals and haven’t infected humans. They tend to morph and mutate, which means the level of risk they pose can change the longer they circulate in humans.

3. How does this coronavirus compare with others?

It’s genetically similar to the SARS virus but appears milder in terms of severity and fatality rate. With SARS, about 9% of reported cases died. A related virus, known as MERS-CoV, that’s been spreading since 2012, has led to death in 34% of the 2,499 cases recorded. By contrast, an estimated 50 million people died in the 1918 influenza pandemic that had a case-fatality ratio of less than 5%, but infected up to a third of the world’s population.

4. How do people contract the virus?

Most likely by coming into contact with virus-containing droplets that are emitted when an infected person breathes, talks, coughs or sneezes. These can be transferred directly to someone else in close proximity or via hands and surfaces. There’s a theoretical risk the virus can spread through feces or farther through the air in tiny particles known as aerosols. People who are still incubating the virus and show no symptoms may spread it. There have been reports in China, including that of a seemingly healthy 10-year-old boy who apparently passed the virus to family members. However, asymptomatic transmission is unlikely to become a major factor in the spread, Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases in the U.S., said Jan. 28.

5. How infectious is it?

Epidemiologists try to gauge contagiousness by estimating the number of additional people a person who is infected is likely to infect. That measurement, called a basic reproduction number, is one indicator of how difficult an epidemic is to control. The WHO gives a preliminary range of 1.4 to 2.5 for 2019-nCoV. At the high end, that makes it similar to SARS and more infectious than flu. A group from the Chinese Academy of Sciences in Beijing estimated the number to be 4.08.

6. What does the virus do?

Infections appear to cause a mild illness in children, adolescents and younger adults, and more severe disease in older people. Frequently reported early signs are fever, dry cough and tiredness -- but not the sneezing and runny nose typical of a cold. Studies suggest the virus invades cells in the lower respiratory tract and migrates from there to the lungs, causing difficulty breathing and the inflammation and congestion associated with pneumonia. In an early study, more than a quarter of hospitalized patients developed a potentially fatal complication known as acute respiratory distress syndrome. Septic shock, respiratory failure and the failure of other organs have also been seen. Many of the fatalities have been in patients with underlying illnesses such as cardiovascular disease.

7. Where did it come from?

The virus emerged in early December in Wuhan, an industrial city of 11 million. Early attention focused on a seafood market where live animals were also sold, but about a third of the first 41 cases were found to have no link to it. The viral genome is even more closely related to several coronaviruses found in bats than it is to the SARS coronavirus. Diseases transmissible from animals to humans, sometimes referred to as “zoonoses,” comprise a large percentage of all newly identified infectious diseases.

8. How alarming is a new virus?

There is always concern when a new pathogen emerges in people because they typically lack immunity to it and there usually aren’t specific treatments or vaccines available. Novel coronaviruses, those not seen in humans before, represent a particular concern because they have been known to spark complicated outbreaks that have sickened thousands of people, like SARS did as it swept across the globe from southern China.

9. How worried should I be?

Unlike SARS, relatively few cases have been reported outside mainland China. But in Hubei, thousands of people have been hospitalized in isolation wards and hundreds are being treated in intensive care units, creating what officials there have described as an “extreme, severe and abrupt public health crisis.” A Wuhan hospital saw coronavirus infections spread rapidly among health-care staff and other patients, according to a study published in the Journal of the American Medical Association.

10. What are authorities doing?

China’s government imposed a quarantine on Wuhan and more than a dozen other cities in the region, a travel ban covering in excess of 50 million people. New hospitals were built from the ground up in days, and the production of medical equipment ramped up. Patients were isolated to prevent any spread. Health officials are looking for, screening and monitoring people the patients had contact with. School holidays have been extended and work-from-home orders issued. The WHO has declared the outbreak a global health emergency, a designation that can help mobilize international responses. Anyone caught spreading misinformation was subject to criminal charges in some Asian countries. The U.S. State Department has advised people not to travel to China and said those already in the country should consider leaving. Hong Kong, the international financial center that functions with some autonomy from China, announced its own travel restrictions from the mainland. The U.S., Australia, India and other countries were denying or restricting entry for non-citizens arriving from China in an attempt to stop the virus’s spread, although the WHO has called such measures unnecessary.

--With assistance from Dong Lyu, Hannah Dormido, John Lauerman and James Paton.

To contact the reporter on this story: Jason Gale in Melbourne at

To contact the editors responsible for this story: Michael Patterson at, Paul Geitner, Lisa Beyer

©2020 Bloomberg L.P.