Two consecutive thunderstorm associated epidemics of asthma in the city of Melbourne. The possible role of rye grass pollen

Objective: To document the clinical impact and identify the meteorological and environmental circumstances surrounding two epidemics of asthma exacerbations associated with thunderstorms in the city of Melbourne and to find a possible aetiology for these events. Design: Collection of meteorological and environmental data from the Victorian Bureau of Meteorology and the Environment Protection Authority; collection of clinical data from metropolitan emergency departments and the Victorian Ambulance Service; and study of a cohort of affected patients with asthma and a control group of asthmatics who were not affected by the storms. Setting: Tertiary institution. Patients: Twelve storm-affected patients with asthma and 16 asthmatics not affected by the storms. Intervention: Administration of a questionnaire, medical interview, pulmonary function tests and skin prick tests with common allergens. Main outcome and results: Both epidemics caused a major increase in the number of hospital attendances and admissions because of asthma exacerbation (five to ten fold rise). These events could not be related to atmospheric pollution or specific meteorological features of the storms. Patients affected by the second storm were significantly more likely to suffer from hay fever (P < 0.05), rye grass pollen allergy (P < 0.05) and allergy to rainfall released rye grass starch granules (P < 0.025). Conclusions: Late spring thunderstorms in the city of Melbourne can trigger epidemics of asthma attacks. The seasonal nature of the phenomenon and the pattern of allergic responses found in affected patients suggest a possible aetiological role for rye grass pollen.