A phenomenon called 'thunderstorm asthma' caused a huge spike in calls to Ambulance Victoria on Monday, but what is it and how does it occur?
Dr Megan Howden is a respiratory and sleep physician in Melbourne.
If you suffer from itchy eyes, a runny nose, headaches and excessive sneezing this time of year, you’re certainly not alone. Hay fever or allergic rhinitis is an allergic reaction to pollen and affects one in six Australians.
But when you combine high pollen counts with thunderstorms and warm weather, a much more serious phenomenon can unfold: thunderstorm asthma attacks.
Grass pollen is usually too large to enter the small airways of the lungs and is filtered out by the nose, causing hay fever in those allergic to pollen.
But stormy winds and moisture can cause the pollen to rupture into tiny particles, which are small enough to be inhaled.
The outflow winds of a thunderstorm then concentrate these tiny particles at ground level, where they can easily enter the small airways of the lungs and cause an acute asthma attack in those who are allergic to grass pollens.
The symptoms of thunderstorm asthma can occur quickly and include shortness of breath, chest tightness, coughing and wheezing.
Who does it affect?
Thunderstorm asthma commonly affects young adults with a history of hay fever but not necessarily of asthma. And of those with a previous diagnosis of asthma, many claimed it wasn’t severe enough to warrant preventer medication.
After the Wagga Wagga thunderstorm asthma epidemic in October 1997, researchers compared the data of those who experienced a thunderstorm asthma attack with those who had an asthma attack on other days of the year (the control group).
They found that 95 per cent of those affected by thunderstorm asthma had a history of hay fever and 96 per cent tested positive to grass pollen allergies.
Of those with a history of asthma, only one in four (27 per cent) of affected cases were taking regular preventer inhalers compared with more than half (56 per cent) of the control group.
This suggests that regular use of asthma preventer medication, at least during spring, may protect those with asthma and grass allergies from thunderstorm asthma attacks.
How is it treated?
The best way to treat thunderstorm asthma is to prevent it occurring, where possible. So good asthma control is essential.
Anyone with asthma who has allergy symptoms in spring (including hay fever, or worsened asthma symptoms) should use a regular preventer inhaler, even if they feel well. These inhalers are designed to reduce the inflammation in the lungs over a period of time, and prevent an asthma attack occurring.
All asthma sufferers should have a written action plan from their doctor, which describes the steps to be taken if symptoms escalate.
In the event of a thunderstorm asthma attack, treatment will be the same as any other acute asthma attack, which usually involves the administration of inhaled mediation to dilate the airways, plus an anti-inflammatory medication.
What regions are affected?
Thunderstorm asthma was first described in Melbourne in 1987 and has occurred in other parts of the country (south-eastern Australia is particularly vulnerable) and the world, including in England and Italy.
The most recent epidemic occurred in Melbourne on 25 November 2010 after the onset of a thunderstorm, when grass pollen counts were in the extreme range.
Shortly after the thunderstorm began, the Melbourne metropolitan ambulance service was inundated with calls for assistance from people who had trouble breathing and the ambulance disaster management plan was enacted.
Austin Health, a large metropolitan hospital in Melbourne, saw a tenfold increase in patients presenting with acute asthma attacks in the 24 hour period following the storm.
Thunderstorm epidemics are uncommon but the prospect of another wet spring/summer means we need to be vigilant. If you have difficulty breathing – whether you have a history of asthma or not – call 000 for an ambulance immediately.
Megan Howden does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond the academic appointment above.
Editor's note: This explainer was originally published in 2011.