In 2016, The World’s Deadliest Thunderstorm Asthma Event Occurred. Now We Know What Caused It

On November 21, 2016 hospital emergency wards across Melbourne, Australia were suddenly overrun with patients with severe respiratory problems. Ten people died and thousands struggled to breathe for frighteningly long periods. The event was not a forerunner of a viral epidemic, but the worst case of a phenomenon known as “thunderstorm asthma”. Scientists have now revealed that the commonly believed explanation for these events is wrong, and that they are triggered by lightning, not rain.

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South-eastern Australia appears to be the worst place in the world for thunderstorm asthma, but the US has had several rounds and CSIRO's Dr Kathryn Emmerson told IFLScience the UK has experienced some as well. It's likely they are happening more widely on a less severe level that doesn't attract the same attention as a single big event, but cumulatively causes far more harm. If one coincided with a viral outbreak like COVID-19 things could get far worse, making predicting them a priority.

The popular explanation in the wake of Melbourne's event was that rain had caused widespread pollen to burst, releasing sub-pollen SPPs. These produce a similar allergic reaction to ordinary pollen, but penetrate deeper into the lungs, with more serious consequences.

Emmerson is first author of a paper in PLOS ONE that notes this theory doesn't fit the facts. The storm in question was accompanied by relatively little rain, and the rise in humidity came well after hospitals reported overloads of people fighting for breath. The authors present an alternative explanation.

Although Emmerson admitted to IFLScience the team is not certain SPPs are responsible for thunderstorm asthma, they do think that part of the theory is probably right. “The people who presented to emergency departments, most didn't have histories of asthma," Emmerson said. “But they did have hayfever histories. Also, it happened right at the peak of Melbourne's pollen season.” People with asthma histories suffered as well, but had preventers or inhalers, which meant few of them needed medical assistance.

The paper proposes pollen burst open in the rye-grass pastures to Melbourne's west and the particles were swept into the city by the prevailing winds to plague the inhabitants. However, this only works if the bursting coincided with a wave of dry lightning that preceded the rain by several hours.

The authors offer several possibilities as to what would cause the rye-grass pollen to burst including friction from the wind, electrical build-up, and the lightning itself. All may have played a part, but the timing makes lightning the prime suspect

Since 2017 Australia's Bureau of Meteorology has issued thunderstorm asthma event warnings, encouraging those with asthma or hayfever to stay indoors and keep preventers handy. Emmerson told IFLScience her work was done in conjunction with the Bureau, and has already incorporated these warnings. On the other hand, she said, counterpart organizations worldwide only provide pollen alerts and could be taken by surprise by a similar event.

The thunder asthma event in Melbourne saw a 672 percent rise in excess respiratory-related admissions at local hospital emergency rooms and a 992 percent increase in asthma-related admissions to hospital within 30 hours. As the pandemic has shown us, overwhelming hospitals is dangerous and can have long-term knock-on consequences.

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