As the coronavirus outbreak continues in China and beyond, key questions remain about the nature of the virus and how quickly and easily it can spread between people.

Here's a look at some of the potentially serious turns the outbreak could take.

Sustained human-to-human transmission

Human-to-human transmission is the spread of an illness from an infected patient to a non-infected person.

There are two types of this transmission: limited and sustained.

Passengers walk past a sign warning of the virus, at Narita Airport in Japan last week. (JIJI PRESS/AFP/Getty Images)

Limited human-to-human transmission occurs when there is close contact between those who have the virus and those who don't, particularly with family members, but is usually contained to a small number of people before running its course.

Sustained transmission is characterized by the World Health Organization as an illness that can transmit easily from one person to others in the population.

"It is now clear from the latest information that there is at least some human-to-human transmission. Infections among health-care workers strengthen the evidence for this," the WHO in China said in a statement Monday.

"In addition, information about newly reported infections suggests there may now be sustained human-to-human transmission. However, we still need more analysis of the epidemiological data to understand the full extent of human-to-human transmission."

WHO officials will convene an emergency committee on Wednesday in Geneva to determine whether the outbreak constitutes a public health emergency of international concern and to discuss what recommendations should be made to manage it.

"The key issues here are what is the extent of human-to-human transmission and how easy is human-to-human transmission?" said Isaac Bogoch, an infectious diseases specialist at Toronto General Hospital.

"That's going to be a factor into how widespread this ultimately gets."

Travellers wear masks as they walk outside of the Beijing Railway Station on Jan. 20. The coronavirus outbreak coincides with the country's busiest travel period, as millions board trains and planes for the Lunar New Year holidays. (Mark Schiefelbein/The Associated Press)

Mutation of the virus

Health officials will also be watching closely to see if the virus changes as the outbreak continues, said Dr. Kamran Khan, an infectious disease physician and scientist at St. Michael's Hospital in Toronto.

"Viruses evolve and mutate, and they may start to take on new attributes and characteristics that either make them more easily transmissible or make them more deadly," he said.

"The reality is that the longer that it's out there, the more it will evolve."

Dr. Allison McGeer says if the coronavirus mutates into something more contagious, that would be a 'significant concern.' (Craig Chivers/CBC)

Dr. Allison McGeer, an infectious diseases specialist at Mount Sinai Hospital in Toronto, said if the coronavirus mutates into something more contagious, that would be a "significant concern" similar to the way in which SARS evolved.

McGeer said the initial clusters of patients infected with SARS in early 2003 were associated with open-air markets in China, much like in the current coronavirus outbreak, with limited transmission from person to person.

"Then over the next couple of months, the virus evolved into a virus that was more transmissible person to person, but more transmissible person to person when people were seriously ill," she said.

"If that process is repeating itself, and the virus is changing, then we may be moving from one problem to a completely different problem. So far that's not what it's looked like, but I don't think you can be sure about it."

McGeer added there haven't been many reports of transmission to health-care workers, aside from the reported 15 cases of medical staff in Wuhan , which she said concerns her about the potential for the virus to change.

"They must have followed up with health-care workers after the initial cases in December, they didn't see transmission and now they've found transmission," she said.

"It does raise the concern that this is a virus that is changing and if it's a virus that's changing then that's a whole new set of issues. There's nothing we can do except wait to know what's going to happen."

Possibility of a 'super-spreader'

Another concern is the possibility of a "super-spreader," a highly infectious patient who can spread the illness to many people at a disproportionate rate to other carriers.

The U.S. Centers for Disease Control said super-spreader events were "pivotal" in the spread of SARS worldwide in 2003.They defined super-spreading as transmission to at least eight people.

One super-spreading event was identified early in the epidemic in Beijing, where a patient with an onset of SARS two months after hospital admission was the source of transmission to 76 patients, including 12 health-care workers and several hospital visitors.

Gabriel Leung, an epidemiologist and family doctor, says 'super spreading' events need to be recognized at the earliest stage. 0:52

Prof. Gabriel M. Leung, dean of medicine at the University of Hong Kong, said Tuesday the "critical issue" in controlling a coronavirus epidemic is to make sure that super-spreading events are controlled quickly.

"It is absolutely critical that public health authorities recognize a super-spreading event in the very earliest stages," he said during a media availability. "Before it goes absolutely explosive."

Dr. Maria Van Kerkhove, acting head of WHO's emerging diseases unit, said the possibility of a super-spreader is top of mind for health officials worldwide.

"There is also the possibility of super-spreading events. The global community is very familiar [with] what has happened with SARS in the past and this is something that is on our radar," she said during a press conference Tuesday.

"That is possible, and what we need to prepare ourselves for."

Khan, who is also the founder and CEO of the company BlueDot that uses data to study how infectious diseases spread around the world, said outbreaks are like fires, and infected individuals are like embers.

"They may land in one location where they happen to just trigger a big outbreak, and it may have to do with a super-spreading event," he said.

"A super-spreading event does not mean that it is limited to the epicentre in Wuhan; it could catalyze multiple new epicentres."