After the tragic deaths of eight people related to the recent outbreak of thunderstorm asthma in Melbourne, we need to consider the “perfect storm” of climate change.
These deaths were the tip of an iceberg of acute illness leading to a surge in ambulance calls and emergency presentations to hospital. It was reported that Ambulance Victoria experienced six times its normal workload on the night of the storm, 8500 people went to Victorian hospitals over that day and the next, stocks of asthma medications ran low and the health system was stretched to capacity.
While not common, thunderstorm asthma has been described in late spring in multiple locations including Birmingham and London in Britain, Calgary in Canada, Naples in Italy, Wagga Wagga in NSW and also previously in Melbourne. While not all such events have necessarily been recorded, the medical literature has examples at least back to the 1980s.
High concentrations of pollen from plants, such as rye grass, can be stirred up by thunderstorms, absorb moisture, swell and burst into smaller particles of fine starch granules containing allergens. While large grass pollen particles can be trapped in the upper airways, causing symptoms of hay fever, these smaller sub-particles can travel further into the airways and lungs, causing breathing problems even in people who have not been previously diagnosed with asthma. It is thought that pollens are caught in the updrafts into the high humidity at the cloud base where they rupture and cold downdrafts carry aerosols of many small respirable pollen fragments to ground level distributing them over a wide area.
When this occurs near a large city a great number of people can be affected and asthma symptoms can be rapid and severe. For example, during the 30 hours after the 1994 London thunderstorm epidemic, nearly 10 times the expected number of patients with asthma or other airway diseases, attended emergency departments. Likewise in Melbourne in 1987 and 1989 up to tenfold increases in asthma presentations to emergency departments were noted over a 24-hour period. We don’t have enough evidence to make any firm predictions about the risk of this sort of event in Sydney although we know there is a strong seasonal relationship between sudden asthma epidemics and the rye grass pollen season in regional inland NSW.
We need more research into the exact triggers for such a major event. For example, airborne allergens can differ from place to place, and understanding local variable factors will be important. However we do already have insights from research into a significant global influence on both extreme weather and plant allergens: climate change.
With climate change we can expect to see more hot days, heavy rainfall events and severe meteorological events. In fact, our health services are already having to adapt to the health impacts of more and longer heatwaves. Increasing atmospheric carbon dioxide and temperatures are also associated with faster plant growth with more pollen produced by each plant, increases in the amount of allergenic proteins in the pollen, along with earlier and longer pollen seasons.
Last year, the World Allergy Organisation warned climate change was causing changes that can put our respiratory health at risk – more severe and prolonged heat waves, variability in temperature, increased air pollution, forest fires, droughts, and floods. “These changes in climate and air quality have a measurable impact not only on the morbidity but also the mortality of patients with asthma and other respiratory diseases … global warming is expected to affect the start, duration, and intensity of the pollen season on the one hand, and the rate of asthma exacerbations.”
To add to the complexity of this picture, there is good evidence that pollution from burning fossil fuels that drives climate change, such as vehicle exhaust, includes particles and gases that directly affects our respiratory and cardiovascular health, and that many of these can worsen asthma. Although air pollution has not been implicated in this acute event, it has a recognised role in worsening asthma through airway inflammation and so is a background concern for those vulnerable to poor respiratory health. Some researchers have postulated that air pollutants help facilitate allergic sensitisation of the airways in predisposed individuals. So global warming will likely increase our exposure to allergens and air pollutants that arise from sources contributing to climate change and may intensify allergic responses.
Health care workers did an amazing job of rising to the challenge of this epidemic. But the challenges will keep coming, and it is clear we need to do more to understand and prepare for the increasing impacts that climate change will have on our health. This involves giving good preventive care as well as treatment to vulnerable individuals, strengthening our health care systems and also taking rapid and effective action against further climate change.
Dr Marion Carey is a public health physician, an adjunct associate professor at the University of Notre Dame School of Medicine Sydney and a member of the management committee of Doctors for the Environment Australia.
First published in the Sydney Morning Herald on 29 November 2016