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Thunderstorm-triggered asthma (TA) is the occurrence of acute asthma attacks immediately following a thunderstorm. Epidemics have occurred across the world during pollen season and have the capacity to rapidly inundate a health care service, resulting in potentially catastrophic outcomes for patients. TA occurs when specific meteorological and aerobiological factors combine to affect predisposed patients. Thunderstorm outflows can concentrate aeroallergens, most commonly grass pollen in TA, at ground level to release respirable allergenic particles after rupture by osmotic shock related to humidity and rainfall. Inhalation of high concentrations of these aeroallergens by sensitized individuals can induce early asthmatic responses which are followed by a late inflammatory phase. Other environmental factors such as rapid temperature change and agricultural practices contribute to the causation of TA. The most lethal TA event occurred in Melbourne, Australia, in 2016. Studies on the affected individuals found TA to be associated with allergic rhinitis, ryegrass pollen sensitization, pre-existing asthma, poor adherence to inhaled corticosteroid preventer therapy, hospital admission for asthma in the previous year and outdoor location at the time of the storm. Patients without a prior history of asthma were also affected. These factors are important in extending our understanding of the etiology of TA and associated clinical indicators as well as possible biomarkers which may aid in predicting those at risk and thus those who should be targeted in prevention campaigns. Education on the importance of recognizing asthma symptoms, adherence to asthma treatment and controlling seasonal allergic rhinitis is vital in preventing TA. Consideration of allergen immunotherapy in selected patients may also mitigate risk of future TA. Epidemic TA events are predicted to increase in frequency and severity with climate change, and identifying susceptible patients and preventing poor outcomes is a key research and public health policy priority.

BackgroundEpidemic thunderstorm asthma (ETSA) severely affected Melbourne, Australia in November 2016. There is scant literature on the natural history of individuals affected by ETSA.ObjectiveA multicentre 12-month prospective observational study was conducted assessing symptomatology and behaviors of ETSA-affected individuals.MethodsWe used a structured phone questionnaire to assess asthma symptom frequency, inhaled preventer use, asthma action plan ownership and healthcare utilization over 12 months since the ETSA. Analysis of results included subgroup analyses of the “current,” “past,” “probable,“ and “no asthma” subgroups defined according to their original 2016 survey responses.ResultsFour hundred forty-two questionnaires were analyzed. Eighty percent of individuals reported ongoing asthma symptoms at follow-up, of which 28% were affected by asthma symptoms at least once a week. Risk of persistent asthma symptoms was significantly higher in those with prior asthma diagnosis, current asthma, and probable undiagnosed asthma (all p < 0.01). Of 442 respondents, 53% were prescribed inhaled preventers, of which 51% were adherent at least 5 days a week. Forty-two percent had a written asthma action plan and 16% had sought urgent medical attention for asthma in the preceding year.ConclusionsFollowing an episode of ETSA, patients experience a pivotal change in asthma trajectory with both loss of asthma control and persistence of de novo asthma. Suboptimal rates of inhaled preventer adherence and asthma action plan ownership may contribute to asthma exacerbation risk and susceptibility to future ETSA episodes. Longer-term follow-up is needed to determine the extent and severity of this apparent change.

Rationale: On the 21 st of November 2016 in Australia, a major thunderstorm-asthma epidemic struck Melbourne with an unprecedented number of emergency presentations, hospital admissions and fatalities. Objectives: We identified affected patients who presented to The Royal Melbourne Hospital, an adult tertiary centre in North-West Melbourne. We aimed to characterize individual patient factors associated with hospital admission and identify biomarkers in patient subgroups that are at risk of being severely affected by thunderstorm-asthma. Methods: Cross-sectional, retrospective analysis of demographics of 240 patients presenting to The Royal Melbourne Hospital on 21 st to 22 nd November 2016 post thunderstorm-asthma event and clinical characteristics of 70 of those patients who subsequently attended an outpatient clinic review. Results: Patients were generally young adults (mean age 35 years), with seasonal rhinitis (96%) and universally (100%) sensitised to ryegrass pollen. Forty-four patients (63%) had a known diagnosis of asthma while 20% reported no previous diagnosis but had symptoms consistent with asthma. Patient characteristics associated with hospitalisation were: uncontrolled asthma symptoms in the month before the thunderstorm-asthma event, symptomatic allergic rhinitis, high blood eosinophilia and lower lung function. Conclusion: Thunderstorm-asthma affects people with seasonal rhinitis, ryegrass sensitisation and can occur without prior history of asthma, with dramatic potential to inundate a healthcare system. Our data suggests that hospitalization, and thus a more severe thunderstorm-asthma exacerbation, was associated with a known history of asthma, prior uncontrolled asthma symptoms, allergic rhinitis, high eosinophil count and lower lung function. These factors may inform strategies to identify those most at risk of thunderstorm-asthma.

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