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BackgroundOn 21st November 2016, Melbourne experienced an epidemic of ‘thunderstorm asthma.’ Although previously described in the literature, risk factors and natural history remain incompletely understood.ObjectiveOur aim was to follow up those presenting to the 3 Emergency Departments (EDs) in our health service during the epidemic, and assess their history for previous asthma, rhinitis, and allergies.MethodsED notes of all respiratory presentations within 48 hours of the thunderstorm event were reviewed and patients with acute asthma included. A standardised questionnaire was devised encompassing asthma diagnosis, undiagnosed asthma symptoms and rhinitis severity. Patients were contacted by phone within 30 days of the event.ResultsThree hundred forty-four patients were identified overall; 263 patients were contactable and completed a phone or mail questionnaire. The mean age was 32.7 ± 19.2 years (range, 6 months–87 years; 25% < 18 years) with 58% male sex. A previous diagnosis of asthma was present in 42% (n = 111), and there was no previous asthma diagnosis in 58% (n = 152). Of those who had no asthma diagnosis 53% had probable undiagnosed asthma. Overall, rhinitis prevalence was 88%, of which 72% were moderate or severe (Allergic Rhinitis and its Impact on Asthma guidelines) and 51% (n = 133) reported a history of grass pollen allergy.ConclusionOur data highlights the importance of atopy and rhinitis as risk factors for epidemic thunderstorm asthma. Better identification of undiagnosed asthma, and implementing treatment of asthma and rhinitis may be important.