TORONTO - People who think the new coronavirus couldn't take off and cause a SARS-like crisis may have forgotten a phenomenon that was a game-changer during SARS — patients called superspreaders.

At present, this new coronavirus doesn't seem to spread easily from person to person, a fact which some people use to argue it will not become the next SARS. Some limited human transmission has occurred, but confirmed cases are few and sporadically seen.

However, several experts suggest that superspreaders, which turned SARS into a global outbreak, could do the same with this new virus. That term refers to people who buck the transmission trend with a given bacteria or virus, infecting many more people than is the norm.

Dutch virologist Ron Fouchier gives a succinct answer when asked if a superspreader could be profoundly alter the pattern of spread with this emerging virus: "Yes."

If the virus infected someone who turned out to be a superspreader, and that person sought care in a hospital that wasn't taking precautions against novel coronavirus infections, this new disease could rapidly begin to resemble SARS.

"I think we would be in big trouble," says Fouchier, who is with Erasmus Medical Centre in Rotterdam. "There were really only very few cases that caused the trouble during the SARS outbreak."

So far there have been 16 confirmed infections with the new virus, 10 of which have been fatal. Cases have emerged from Saudi Arabia, Qatar and Jordan.

After the dust settled from the whirlwind 2003 event and infectious diseases teams traded their emergency response vests for their research coats, it became apparent that the SARS coronavirus hadn't spread very well.

In fact, most people who contracted the virus either didn't infect anyone else, or passed it on to a single person. With that kind of inefficient transmission, an outbreak would normally stall, lacking the momentum to keep itself going.

But during SARS, a select few people inexplicably ended up infecting a dozen, two dozen or more people, turning a disease that might otherwise never have been spotted into a four-month worldwide panic.

SARS went global thanks to a superspreader — a Chinese doctor who infected more than a dozen people at a Hong Kong hotel in late February. One of those people brought the virus to Canada.

In Singapore, one SARS patient infected 62 people. In Toronto, which had several superspreaders, one early case infected 44 others.

In fact, an elderly couple who contracted the virus on the night SARS made its first appearance in a Toronto hospital were both superspreaders.

The woman, who had taken her husband to hospital for a heart problem, brought him back a few days later when he began to suffer from the symptoms that would come to be recognized as SARS. Later, people who traced the spread of the virus through Toronto hospitals would see that she infected three admission clerks, a security guard, five visitors, three nurses and one housekeeper —all within a 2 1/2 hour span.

"She wasn't that sick, actually. I don't even know if she had a fever," says Dr. Donald Low, the Toronto microbiologist who helped lead the city's SARS response.

"But clearly she was excreting a lot of virus ... which then ping-ponged into a massive number of cases throughout the city."

It's not clear why some people became superspreaders during SARS.

True, in some cases the amplified transmission seemed to relate more to the circumstances than actual patient. For instance, it became apparent that intubating a patient — putting him or her on a breathing machine — could be a superspreader event if health-care workers weren't wearing respirators fitted over their noses and mouths and goggles to shield the mucus membranes around their eyes.

Still, there were some people who seemed to spew more virus than others. Why? Maybe it was due to their health status — perhaps they had another medical condition that amped up the amount of virus they emitted, muses Michael Osterholm, director of the Center for Infectious Diseases Research and Policy at the University of Minnesota.

Osterholm thinks it could happen again. "Is there a potential here for a superspreader to be in our midst? I think absolutely. Yes."

"It's the virus and the host and the environment here all interacting. And any one of them could up the ante for widespread transmission. This is why it's kind of a stay-tuned (situation)," Osterholm warns.

Low too thinks it's a possibility.

"These RNA viruses, you just can't predict what they're going to do," he says. (Coronaviruses are RNA viruses, which mutate rapidly.) "So the longer they stay in the human population, the more likely it is they're going to do something that's not good."

"Probably some individuals who come down with this will either come down with it in a different level of their respiratory tract or their receptors are going to be expressing in such a way as that the virus will be able to attach better, replicate better and if it does happen to be in the upper respiratory tract possibly, be able to disseminate better."

If someone with superspreader capacity were to take the virus from the Middle East to another country, that could ratchet up the risk. Wealthy people from the Middle East sometimes fly abroad for medical care. In fact, both of Qatar's confirmed cases were diagnosed in Europe — in Britain and Germany.

The man who went to Germany may have been a bullet dodged. The hospital he went to did not know he was infected with the coronavirus. A report on his case in the journal Eurosurveillance noted some health-care workers in the hospital didn't wear protective gear while treating him.

The man didn't transmit the virus to his health-care providers, but that may have been thanks to the fact he was already on a ventilator when he arrived at that hospital, says Dr. Christian Drosten, a coronavirus expert from the University of Bonn's Institute of Virology.

If he hadn't been on a ventilator already? Who knows whether he might have infected others, and how the virus might have behaved in crowded Germany cities in a cold, humid German winter?

"We have a country (Saudi Arabia) which is not densely populated, apart from say central Riyadh, Dammam and Jeddah. The rest in Saudi Arabia is villages. And you have a very dry, very hot climate, which is also not something viruses like," Drosten notes.

"So we don't know at all what happens if this virus comes to a Northwestern (Europe) big city."

And Europe isn't the only place to watch.

Dr. Kamran Khan, who tracks global travel patterns as a tool to predict and interpret spread of diseases, notes that about 25 per cent of people who travel from Saudi Arabia, Qatar and Jordan — the three countries which have seen cases so far — go to the massively populated countries of South Asia, specifically India, Pakistan and Bangladesh.

"If we look at South Asia, there's obviously a lot of people there. There's high population density. And there's limited resources. And diagnostic facilities are perhaps not as sophisticated as they are in European centres and North American centres," says Khan, who is an infectious diseases doctor and scientist at Toronto's St. Michael's Hospital.

"The key message I think is important for really the whole international community to be mindful of is that our risks are very much connected to the public health capacity and sophistication of the diagnostic tools and systems that are in place in every other country around the world."

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