Four people, including two students, were confirmed dead in the city of Melbourne, Australia, Wednesday from a rare condition known as thunderstorm asthma.
Hundreds more were rushed to hospitals while suffering from asthma attacks. Many had no history of the disease. The local ambulance service, Ambulance Victoria, responded to 1,870 cases Monday evening — about six times the normal traffic, according to the Associated Press.
A wild thunderstorm passed through the area Monday, causing rain-sodden rye grass pollen to explode and disperse all over the city, triggering the attacks and breathing problems, authorities said.
Typically, pollen fragments released on hotter days are too big to enter a person's airway. But heavy rains can cause the pollen to burst into smaller particles and affect breathing when inhaled.
Experts say there is no way to predict the phenomenon, as storms on high-pollen-count days do not always result in thunderstorm asthma.