Epidemic thunderstorm asthma events are uncommon and don’t occur every year, but when they do, they can happen during grass pollen season.

Melbourne experienced the world’s largest epidemic thunderstorm asthma event on 21 November 2016, with thousands of people developing breathing difficulties and requiring emergency department attention, and hundreds of people requiring hospital admission in a very short period of time.

Although there have been other epidemic thunderstorm asthma events previously reported in Melbourne, none have been close to the size and severity of the 21 November event. Five other epidemic thunderstorm asthma events in Melbourne have been recorded in medical literature since 1980.

While there are still many unknowns about the exact mechanism causing epidemic thunderstorm asthma events, we do know that in 2016 many people who were affected were unaware of the risk to their health and of the steps to take to protect themselves and those in their care.