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WORLD: How doctors trace an outbreak

Doctors will often test cases of pneumonia for which they don’t have an easy explanation, especially if they appear in a cluster

In early March, 2003, a man went to an emergency room in Scarborough, Ont., complaining that he was having trouble breathing.

In winter, cases of pneumonia aren’t that unusual. But something about this man’s story seemed off.

His mother, who had recently returned from Hong Kong, had died just a few days before. Other members of his family were sick too.

So doctors decided to place him in isolation. And when a nurse who regularly read Chinese-language media saw a report about a new disease in Hong Kong, the hospital staff started to put the pieces together.

The mystery illness eventually came to be known as Severe Acute Respiratory Syndrome (SARS), which killed 44 Canadians and infected more than 8,000 people worldwide.

And at first, doctors had no idea what they were dealing with.

“It was completely terrifying,” said Dr. Allison McGeer, an infectious disease specialist with the Sinai Health System, who worked on the front lines of the SARS outbreak in Toronto.

“When the first family presented, it was plainly obvious that something was very wrong. But we had no idea what it was.”

There was no test, she said, and very little knowledge of how the virus spread. But in cases like these, thanks to what she calls “shoeleather epidemiology,” doctors are able to figure out what to do.

Here’s how they do it.

Virus tracking 101

Lessons from the SARS outbreak and other big outbreaks are top-of-mind for public health workers right now as they deal with the threat of a novel coronavirus outbreak, centred in China, but that has been travelling around the world.

This time around, though, there are some important differences. Scientists were able to quickly genetically sequence 2019-nCoV, as the virus is currently called, and tests were rapidly developed.

But some of the same techniques used in previous outbreaks still apply.

First, doctors have to identify that something weird is happening.

“It all starts with a set of clinical cases and what we would call an ‘index of suspicion,’” said Dr. Ross Upshur, head of the division of clinical public health at the University of Toronto.

“In other words, this disease doesn’t look like other things.”

Doctors look at cases with an unusual time, place, and person, said Dr. Nelson Lee, a professor in the division of infectious diseases at the University of Alberta, who worked in Hong Kong during the SARS outbreak.

So, for example, if doctors saw way more flu cases than normal for a certain time of year, or an illness seemed to be linked to a specific location, or hit young, healthy people hard, those all might suggest something strange.

“It’s less about the disease itself than it is about the pattern of the disease,” McGeer said. “How many people have it, what their relation is to each other.”

While some hospitals have systems to detect patterns in their patients, it still often comes down to the hospital staff, she said.

Two doctors might be chatting in a cafeteria line and realize that they both saw patients with pneumonia who mentioned visiting a seafood market, she said. “It’s not necessarily odd that two people who frequent that market might have pneumonia. But that both of you noticed it and you ended up having a discussion about it, that means there’s probably more than two.”

Doctors will often test cases of pneumonia for which they don’t have an easy explanation, especially if they appear in a cluster, Upshur said.

“We would run those specimens through all of the known things that we have,” he said. “And if you do that and nothing shows up, then you have an atypical pneumonia.”

If clinicians are sufficiently concerned, or are convinced they have something new, they might be able to do genetic testing to get a better idea of what the disease is, he said.

And then, they have to act on that information.

Identifying who their infectious patient might have been in contact with is a priority, Lee said.

“The public health officials need to go over in great detail where the patient had been to, whom had he or she been in contact with, and travel history, any contact with sick patients, and generate a list of contacts.”

This is done through a very detailed interview, he said.

Stopping the virus

The goal is to stop the chain of transmission.

In the absence of a vaccine, or an effective treatment for a disease, the only way to stop an infectious disease is to keep it from spreading, said Lee.

With the novel coronavirus, “Unfortunately, we do not have a vaccine. We do not have treatment for this virus. So the way to prevent this infection from propagating is proper isolation.”

Upshur agrees. “There might be uncertainty about certain technical aspects of this novel coronavirus, but we know a lot about viruses and how they spread,” he said.

“There is no mysterious new way in which this virus can be transmitted. It’s in droplets. It goes from person to person.”

Stopping that person-to-person transmission can stop the virus. It worked with SARS.

“We got rid of the virus,” McGeer said. “In the end, when it had completely evolved, it was a completely human virus. And we got rid of it from humans by isolating case after case and making sure they couldn’t pass it on.

“And eventually you get down to the last case, it can’t pass it on, and the virus dies.”

This technique can work even if you don’t know all the details about the virus, she said, as long as you can make educated guesses about how it’s transmitted. If you can keep it from spreading, it will eventually die out.

Finding the source

One thing you might want to know, though, is where the virus came from in the first place.

This is “hugely” important, Upshur said. A lot of recent outbreaks have been traced back to animals, he said.

“It’s incredibly important that we identify animal reservoirs for two reasons. One, so we are forewarned and know what the wide extent of possibility is.

“But secondly, so we can start to actually alter human behaviour in ways that do not promote and accelerate the incursion of more and more viruses and bacteria into human hosts.”

If you don’t know where the virus came from, even if you manage to eliminate all the human cases, you run the risk that it could be reintroduced, McGeer said.

“The question of what that source is and whether that source might result in reintroduction is really important, because you don’t want to have to do this again.”

Genetic tracing and case histories can help to figure out where the virus came from.

But we’re much more able to deal with the novel coronavirus than we were during SARS, Lee said. “When I look at what’s happening right now, I think that we are a lot more prepared.”

The virus was identified quickly and a test was quickly made available, he said.

And while we don’t know everything yet about the novel coronavirus, Upshur said, we do know something about coronaviruses in general. “We actually know quite a lot about respiratory viruses, how to respond to them. And we have the infrastructure and architecture of how to respond to them.

“So it’s ‘novel,’ but it’s not brand-new.”

- Global News