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Why are migrants more at risk of asthma in Australia?

As the inquest into a fatal freak thunderstorm asthma event in Melbourne comes to a close, SBS News asks health experts why some people may be at higher risk.

Published 23 August 2018 5:36pm

Updated 23 August 2018 6:24pm

By Kelsey Munro

Image: Ten people died following Melbourne's thunderstorm asthma event in 2016. (SBS News)

A severe weather change around 6pm on 21 November 2016 might have been expected to bring relief from the hot Melbourne day. But instead, it brought an unprecedented crisis to the city as thousands of people suffered breathing problems from severe allergic reactions to grass pollen flung in the air by the storm.

More than 12,700 people presented to emergency departments across Victoria during the crisis, according to a report by the state’s chief medical officer. Ten people died. Six of them were originally from India or Southeast Asia.

It was something “the likes of which in terms of size, severity and acuity had never before been seen, nor even imagined, let alone planned for,” a report into the incident noted. And it has been the subject of an ongoing Coroner’s Court inquest in Victoria, the final submissions of which will be made on Friday 24 August.

Ten people died following Melbourne's thunderstorm asthma event in 2016. Source: SBS News

Why East Asian and Indian migrants?

Within 30 hours of the 2016 storm, 4,000 more people than usual presented to emergency departments with respiratory problems or severe asthma, “especially individuals of Indian or Sri Lankan birth,” according to a major study published in the Lancet Planetary Health journal in June.

While people of East Asian or Indian ethnicity make up 25 per cent of the Melbourne population, 39 per cent of the hospital admissions were from these groups, the study pointed out.

Source: AAP

Dr Naghmeh Radhakrishna, a respiratory, sleep and allergy specialist at Melbourne’s St. Vincent’s hospital and at the private practice East Melbourne Heart and Lung, told SBS News that Asian people generally don’t have as high a prevalence of hay fever and asthma.

“After they move to Australia that’s when you see an increase in the prevalence of these symptoms," she said.

She cited a key research paper published by Dr Roland Leung in 1994 which found migrants to Australia were more likely to develop symptoms the longer they stayed in the country.

“Part of that is going to be related to the fact that they’re not exposed to the kinds of allergens we have in Australia, for example the ryegrass,” Dr Radhakrishna said.

Ryegrass is a very common grass in south-eastern Australia.

“So when they come to Australia for a few years, typically it will take five to ten years, they become sensitised ... so they start to experience these allergy symptoms; hay fever, runny nose, itchy eyes, sneezing, itchy throat, itchy ears.”

Some of the pollen that was flying around Melbourne on November 2016 as a consequence of the thunderstorm. Source: AAP

Professor Janet Davies, head of allergy research at Queensland University of Technology, who was also on the lead author team in the Lancet Planetary Health study, said no one yet understands the reasons why different population groups have different sensitisations to grass pollen.

“It’s definitely intriguing,” she told SBS News. “It might be a whole suite of environmental exposures that modify how their immune systems respond, but it may be about exposure to different kinds of allergens as well.

Head of allergy research at Queensland University of Technology, Professor Janet Davies. Source: Queensland University of Technology

“It might be that things like diet, your microbiome inside your gut, and how these factors influence your immune system. It’s definitely a complex interaction between your predispositions or your genes, and the environment you live in - probably involving multiple layers that affect the expressions of allergic diseases in migrants.”

What is thunderstorm asthma?

According to the National Asthma Council, “epidemic thunderstorm asthma is an unusual cluster of allergic asthma flare-ups associated with some types of thunderstorms in spring or early summer ... caused by the combination of high grass pollen counts, unusual thunderstorm conditions that concentrate pollen grains or allergens, and grass pollen allergy in individuals.”

There have been around 23 documented incidents of thunderstorm asthma in the world since the early 1980s, mostly in Victoria (where it was first described) and in the UK.

The event tends to occur in temperate regions where there is a lot of grass during the grass pollen season, which in Melbourne is October to December.

All the contributing factors and mechanisms are not fully understood, but the lead hypothesis is that on extreme pollen days the high wind gusts and humidity in the air during a thunderstorm cause the grass pollen grains to burst and release tiny allergen-containing particles.

“Inside the pollen grain are hundreds of tiny little starch granules which get released and become aerosol particulates that are tiny enough to be breathed in,” Professor Davies said.

Who is at risk?

The 2016 incident was “for many of those affected ... their first asthma attack”, the Victorian Chief Medical Officer’s reported, meaning some people may not be prepared for a future event.

According to the National Asthma Council, “people at risk of acute asthma flare-ups triggered by a thunderstorm include those with seasonal allergic rhinitis (with or without asthma), those with a history of asthma, and those with undiagnosed asthma.”

Professor Davies said in Australia the biggest risk factor is the “ryegrass pollen trifecta”, which means sensitisation to ryegrass pollen, springtime hay fever, and exposure to high levels of ryegrass pollen during the thunderstorm.

How can you protect yourself?

Dr Radhakrishna said there are treatments available if you know you are at risk which will mitigate the severity of a thunderstorm asthma incident.

“If you do have asthma symptoms – shortness of breath, chest tightening and a wheeze, especially during spring, you need to be seeing a doctor to see if you do have asthma.

“If you do have asthma, you should be compliant with your medication and perhaps you should be asking your GP about having an asthma action plan. And make sure you have a reliever at hand, such as a Ventolin or Asmol inhaler. Carry it with you, keep it readily available.”

Staying indoors is likely to help. She also recommends the apps and warning system provided by the Professor Davies’ AusPollen forecast which alert users to potentially hazardous pollen counts in their region.

In an emergency call an ambulance immediately on 000.

For more information on thunderstorm asthma call the 1800 ASTHMA Helpline (1800 278 642) or visit: pollenforecast.com.au, asthmaaustralia.org.au and nationalasthma.org.au