The Role of Fungal Spores in Thunderstorm Asthma

Robert E. Dales, MD, MSc, Sabit Cakmak, PhD, Stan Judek, MSc, Tom Dann, MEng, Frances Coates, MLT, Jeffrey R. Brook, PhD, Richard T. Burnett, PhD


CHEST. 2003;123(3) 

In This Article

Abstract and Introduction


Study objectives: To document the existence and investigate the etiology of "thunderstorm asthma," which has been reported sporadically over the past 20 years.
Design: We assessed the relationship between thunderstorms, air pollutants, aeroallergens, and asthma admissions to a children's hospital emergency department over a 6-year period.
Results: During thunderstorm days (n = 151 days) compared to days without thunderstorms (n = 919 days), daily asthma visits increased from 8.6 to 10 (p < 0.05), and air concentrations of fungal spores doubled (from 1,512 to 2,749/m3), with relatively smaller changes in pollens and air pollutants. Daily time-series analyses across the 6 years of observation, irrespective of the presence or absence of thunderstorms, demonstrated that an increase in total spores, equivalent to its seasonal mean, was associated with a 2.2% (0.9% SE) increase in asthma visits.
Conclusions: Our results support a relationship between thunderstorms and asthma, and suggest that the mechanism may be through increases in spores that exacerbate asthma. Replication in other climates is suggested to determine whether these findings can be generalized to other aeroallergen mixes.


Increased asthma morbidity during thunderstorms has been reported sporadically over the past 2 decades, but the underlying mechanism has not been established. On July 6 and July 7, 1983, the number of patients with asthma presenting to the emergency departments of eight Birmingham (United King-dom) hospitals averaged 50 over the 2-day period, compared to a usual average of 10 visits.[1] The increase in visits was associated with an increase in airborne fungal spores, particularly Sporobolomyces and Didymella, and a decrease in pollen. Airborne pollutants represented by smoke and sulfur dioxide were not believed to be unusually elevated. The authors of the report suggested that asthma may have been caused by an increased release of fungal spores due to an initial rainfall. During a thunderstorm 11 years later (June 24 and June 25, 1994), the number of patients presenting with asthma or other airways diseases to emergency departments in the London area increased 10-fold. "Out-of-hours calls" to general practitioners also increased during this time, in south and east England.[2] This thunderstorm was described as unusually large and multicentered, and was associated with reduced temperatures and severe wind gusting.[3,4] A high level of grass pollen occurred 9 h previously.[4]

Meteorologic risk factors for daily asthma admissions during 1987 and 1994 were investigated, using the English Hospital Episodes System database. Fifty-six "epidemics," defined as an exceptionally high number of asthma hospital admissions compared to the week before and the week afterward, were identified. Risk factors for asthma epidemics included increased temperature, increased rainfall, increased lightning flashes, and the combination of lightning flashes and elevated grass pollen.[5]

In the southern hemisphere, "thunderstorm asthma" epidemics have been reported in Australia.[6] Fivefold to 10-fold increases in emergency visits to major hospitals in Melbourne occurred during two 24-h periods in 1987 and 1989. Meteorologic associations included increased rainfall and humidity, a drop in temperature, and no change in ambient pollutants. Aeroallergens were not discussed.

There are several limitations to our understanding of the association between thunderstorms and asthma. First, there have been few reported observations of this phenomenon over the past 25 years. Secondly, associations have often been based on simple descriptive statistics, and occasionally on multivariable analysis that did not adjust for serial autocorrelations.[7,8] Finally, attributing the increase in asthma to one factor -- grass pollen, for example -- is difficult if other plausible factors have not also been simultaneously accounted for, such as temperature, air pollutants, and fungal spores.[9,10]

A recent study by Lewis et al[11] used time-series analyses to account for serial autocorrelations. Fungal spores tended to increase while grass pollen decreased on thunderstorm days, but the level of statistical significance was not reported. Interest-ingly, grass pollen influenced asthma only on days when there was light rainfall. Our previous report detected an association between fungal spores and emergency asthma visits independent of thunderstorms.[12]

To address the issue of thunderstorm asthma, we determined if both asthma hospital admissions and aeroallergens increased during thunderstorms. We then tested whether the allergens that increased during thunderstorms were associated with asthma exacerbations on a daily basis irrespective of the presence or absence of thunderstorms. In summary, we explored the hypothesis that thunderstorms, by increasing aeroallergen levels, cause asthma exacerbations. Analysis was done using 6 years of emergency department visit data with approximately 4,000 asthma hospital admissions yearly. Air pollution, meteorologic factors, and aeroallergen levels were accounted for simultaneously.


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