Thunderstorm-asthma has made headlines in Victoria recently after claiming the lives of two people and hospitalising dozens more, however, this phenomenon is far from new. Thunderstorms have been linked to asthma epidemics, especially during the pollen seasons, and there are descriptions of asthma outbreaks associated with thunderstorms, which occurred in several cities, prevalently in Europe (Birmingham and London in the UK and Napoli in Italy) and Australia (Melbourne and Wagga Wagga).
It has been demonstrated that changes in the weather, such as rain or humidity, may induce hydration of pollen grains and sometimes also their fragmentation, which generates atmospheric biological aerosols carrying allergens.
During the first phase of a thunderstorm, pollinosis subjects may inhale a high concentration of allergenic material dispersed in atmosphere, which can induce asthmatic reactions and sometimes even severe ones. In other words, there is evidence that under wet conditions or during thunderstorms, pollen grains may, after rupture by osmotic shock, release into the atmosphere part of their content, including respirable, allergen-carrying cytoplasmic starch granules (0.5–2.5 μm) or other paucimicronic components that can reach lower airways inducing asthma reactions in pollinosis patients.
Fortunately, although it can induce severe asthma, outbreaks associated with thunderstorms are neither frequent nor responsible for high entity of disease exacerbations. However, the mechanisms involved in the release of allergens from pollens during thunderstorm should be known so that pollinosis patients can receive information about the risk of an asthma attack also in subjects affected only by seasonal allergic rhinitis.
Although thunderstorm-associated asthma outbreaks are not frequent, it is possible to observe in clinical practice single cases of patients with deterioration of the allergic respiratory symptoms during a thunderstorm and this possibility should be considered, because the frequency of thunderstorms is recently increased in some geographical areas, particularly in temperate and subtropical climate.
The characteristics of described epidemics of thunderstorm-associated asthma can be summarized as follows:
- There is a link between asthma epidemics and thunderstorm.
- The epidemics related to thunderstorm are limited to seasons when there are high atmospheric concentrations of airborne allergenic pollens.
- There is a close temporal association between the start of the thunderstorm and the onset of epidemics.
- There are not high levels of gaseous and particulate components of air pollution.
- Subjects with pollen allergy, who stay indoors with window closed during thunderstorm, are not involved.
- There is a major risk for the subjects who are not under antiasthma correct treatment, but subjects with allergic rhinitis and without previous asthma can experience severe bronchoconstriction.
In the light of the above, subjects affected by pollen allergy should be alert to the danger of being outdoors during a thunderstorm in the pollen season, as such events may be an important cause of severe exacerbations of asthma
In other words, when asthmatic patients realize that a thunderstorm is approaching the best thing for them to do is to stay indoors, with windows closed.
D’Amato, G., Liccardi, G. and Frenguelli, G. (2007), Thunderstorm-asthma and pollen allergy. Allergy, 62: 11–16. doi:10.1111/j.1398-9995.2006.01271.x
