Australia's Bizarre Outbreak: What Is 'Thunderstorm Asthma'?

Hundreds of people in Melbourne, Australia, experienced breathing problems during a recent storm, in what's being called an outbreak of "thunderstorm asthma." But what's behind this rare phenomenon? On Monday (Nov. 21) evening, the ambulance service in Melbourne, called Ambulance Victoria, received more than 1,800 calls during the storm, which is about six times more than usual, according to the BBC. About 200 calls were for cases of asthma, and 600 calls were for people with breathing difficulties, Mick Stephenson, executive director of emergency operations at Ambulance Victoria, told the BBC.