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Detailed description of thunderstorm asthma event and triggers for such an event, by Dr. Danny Csutoros.

Dr Danny Csutoros, Senior Medical Adviser

Hello, I’d like to take this opportunity to explain, in a little more detail, what occurred on the 21st November 2016 and exactly what is Thunderstorm Asthma. Well, Monday the 21st saw an enormous amount of people in greater Melbourne and Geelong suddenly develop asthma. This was the result of Thunderstorm Asthma but I prefer to use the term ‘Epidemic Thunderstorm Asthma’, as the additional word ‘Epidemic’ better describes the event, which not only involved asthma being triggered, but in numbers that were vastly above and beyond what would normally have been expected and it’s this huge number of asthmatic patients, all at once, that has the potential to overwhelm the health system’s capacity to respond.

So, Epidemic Thunderstorm Asthma is a description of an event. It’s an uncommon event, where lots of people suddenly develop asthma and where the trigger from that asthma results from a unique combination of a certain type of thunderstorm and high levels of grass pollen. There have been 6 episodes of Thunderstorm Asthma in Melbourne in the last 32 years. None of the previous 5 came close to the size and severity of last November, which involved thousands of cases of asthma and, tragically, resulted in the deaths of a number of Victorians but let’s go back to the beginning and let me quickly explain what asthma is.

Asthma affects about 1 in 9 people and can start at any age, even in adulthood. Some people have mild and infrequent symptom, whilst, in others, it can a life-threatening disease and we should remember that approximately 1 person dies from asthma every day of the year in Australia. The most important symptoms of asthma are wheezing, shortness of breath, chest tightness and coughing. These symptoms typically come and go, are often worse at night and early mornings and, sometimes, only happen in certain times of the year.

People with asthma have a response to certain triggers that respond to certain triggers that cause the small airways deep in the their lungs to, firstly, constrict and, secondly, become inflamed, resulting in swelling and the production of mucous. Together, this narrows or even blocks the small airways in the lungs, making it difficult to breathe, with a sense of chest tightness and may cause an audible wheeze and cough. Different people have different triggers for their asthma, which may include viral upper respiratory tract infections, exercise, changes in the temperature, smoke and allergies to things such as house dust mite, pollens, moulds and pets.

Epidemic Thunderstorm Asthma is an uncommon trigger that, one, by its very nature, affects many people at once. So, what actually happened? Well, we know that leading up to November 2016, there was lots of rain, resulting in lots of grass growing in the western parts of Victoria. On that Monday, it was a hot, sunny day and the grasses would have opened to release their pollens. Then, there was a severe and large organised thunderstorm that moved across Victoria from the west. As you can see in this image, the updraughts of the storm picks up the pollen and the moisture in the clouds bursts the pollen grains to release many small allergenic materials and these are so small that they can get through the nose and reach down deep into the lung and trigger asthma. This happened after 5pm that Monday, when lots of people were outside and exposed. From looking back at the past, we have noticed that all Epidemic Thunderstorm Asthma events in Melbourne have occurred in November, which is the height of grass pollen season. All followed a thunderstorm but not all thunderstorms in pollen season resulted in Epidemic Thunderstorm Asthma events. All have occurred when there was high pollen levels but high pollen levels don’t always result in these events.

There is still lots we need to learn about the detailed science of these complex events and research and investigation is planned, so we may better forecast these events into future.

Thank you.