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.