An outbreak of a deadly virus in South Korea has set off alarms across the region.
In the past week, South Korea's confirmed cases of the Middle East respiratory syndrome have more than tripled to 41, with at least three deaths. About 1,600 people are quarantined and more than 1,000 schools are closed.
It's the largest outbreak of MERS outside Saudi Arabia. And researchers around the world have been trying to figure out why the outbreak in South Korea has gotten so large, so fast.
Now researchers have a clue: a superspreader event.
In the past, MERS hasn't been very contagious — at all. The virus is actually lousy at spreading from person to person. On average, a person who catches MERS passes it on to only one person, or even nobody.
So outbreaks peter out, because there's no "sustained transmission," as epidemiologists say.
But then last month, something unusual happened. A businessman, age 68, picked up MERS in the Middle East and brought it to South Korea. It was the first time MERS was in the country. And before health officials knew he had MERS, he had visited at least three hospitals and likely spread MERS to more than 20 people.
The big question is why is MERS suddenly spreading like a cold — or worse? "What we now see in South Korea is kind of interesting and kind of worrying," says Vincent Munster, who leads the viral ecology unit at the National Institute of Allergies and Infectious Diseases in Montana. "So we really have to figure out what's going on there."
One scary idea is that the virus has changed or mutated so it's now more contagious.
"It's always possible that a virus can change. That's a general rule," says Christian Drosten, a virologist at the University of Bonn in Germany. But it takes not just one but several changes for a virus to become more contagious. "And the probability for these to happen together is really very, very low," he says.
Drostan has been on the ground in Saudi Arabia, working with the Ministry of Health to track MERS around the country. He says sometimes he finds patients who make more virus in their lungs.
"If we look at data that we have [from Saudi Arabia] that are not published yet, what we can say is there are some patients that have extraordinarily high viral loads," Drostan says.
And when these so-called superspreaders cough, he says, they can infect many people, sometimes a dozen or more.
"Maybe the index case in Korea was one of those superspreaders," Drosten says.
And here's the key thing about this superspreader theory: Drosten thinks that MERS superspreaders are quite rare, although he doesn't know the exact the percentage.
So if his theory is right, people who caught MERS from the businessman aren't likely to pass the virus onto others. And if that's the case, the outbreak should be over quite quickly, maybe in a week or so.
AUDIE CORNISH, HOST:
An outbreak of the deadly virus MERS in South Korea has set off alarms across the region. Here's the breakdown of the numbers right now. There are 36 confirmed cases and three deaths. About 1,600 people are quarantined. More than a thousand schools are closed. NPR's Michaeleen Doucleff reports on what we know about the virus and the chances that it could start the next big pandemic.
MICHAELEEN DOUCLEFF, BYLINE: For a virus to cause a pandemic, there's a top requirement. It needs to be able to spread easily from one person to the next, like the cold virus. And on the surface, MERS looks like a really scary version of the common cold. It starts off as a cough and a fever, and it's even in the same family of viruses as the cold. Vincent Munster is a virologist at the National Institute of Allergy and Infectious Diseases in Montana. He says there's a big difference between the two viruses - how they spread. The common cold infects the upper respiratory tract - your sinuses and your nose.
VINCENT MUNSTER: That's why you get those tell-tale signs of a common cold, so you got a runny nose.
DOUCLEFF: And stuffed-up sinuses, so when you sneeze, lots of virus comes flying out of your nose onto other people. And they can stick on things like doorknobs, your fingers. So the cold virus spreads very quickly. But Munster says the MERS virus couldn't care less about the nose.
MUNSTER: They really target directly the lower respiratory tract - the lungs.
DOUCLEFF: Deep, deep in the lungs, so when a person with MERS coughs or sneezes, not much of the MERS virus comes up. So the virus doesn't spread very easily. In fact, MERS is so lousy at spreading that people typically pass it on to just one person, if anyone. Outbreaks just peter out. So it looks like MERS cannot cause a pandemic. But then last month, something unusual happened. A man picked up MERS in the Middle East, brought it to South Korea, and then, it looks like he spread it to at least 20 people. That's right - two-zero.
MUNSTER: What we now see in South Korea is kind of interesting and kind of worrying, so we really have to figure out what's going on there.
DOUCLEFF: Has the virus changed or mutated in some way? Is it now more contagious and on its way to pandemic status? Well, Christian Drosten, a virologist at the University of Bonn in Germany, laughed at that idea.
CHRISTIAN DROSTEN: (Laughter). It's always possible that a virus can change. That's a general rule. But such a virus usually needs not just one but several of these changes, and the probability for these to happen together is really very low.
DOUCLEFF: Drosten has been tracking MERS in Saudi Arabia which has seen hundreds of cases. He thinks there's something else going on in Korea. He says sometimes people with MERS become super-spreaders.
DROSTEN: If we look at data that we have that are not published yet, what we can say is, there are some patients who have extraordinarily high viral loads.
DOUCLEFF: Their lungs just fill up with tons of MERS, so they're more likely to spread it.
DROSTEN: Some call them super-spreaders, right? And maybe the index patient in Korea was one of those people.
DOUCLEFF: And here's the key thing. Drosten says MERS super-spreaders are rare. So if his theory is right, people who caught MERS from the man who carried it to Korea won't pass the virus on to others, and the outbreak should be over in a week or so.
So you don't feel like this outbreak is something to be very alarmed about.
DROSTEN: No. I'm not alarmed. No, no. I think this is really within the normal range.
DOUCLEFF: And even if his theory is wrong, Drosten says South Korean health officials are doing everything they can to stop the outbreak. Michaeleen Doucleff, NPR News.
CORNISH: OK. NPR's Brian Naylor. Thanks so much. Transcript provided by NPR, Copyright NPR.