Patients with thunderstorm asthma or severe asthma in Melbourne: a comparison

The Melbourne epidemic thunderstorm asthma (ETA) event of 21/22 November 2016 was unprecedented in size and health impact.1 There is an urgent need to understand the characteristics of the people who were affected. We therefore sought to characterise the patients with ETA who attended Austin Health, a metropolitan teaching hospital in the northern suburbs of Melbourne, during the event, and to compare them with patients with severe asthma.

The study was approved by the Austin Health Human Research Ethics Committee (reference, LNR/17/Austin/319). All adults who attended the emergency department with a diagnosis of asthma on 21/22 November were offered an appointment with a dedicated ETA clinic. Patients underwent clinical assessment and completed the Asthma Control Questionnaire. Spirometry before and after bronchodilator use, radio-allergosorbent testing (RAST), and skin prick testing for aeroallergens were undertaken, and exhaled nitric oxide, total serum IgE, and peripheral blood eosinophil count assessed. Data for the adult patients with ETA were compared with those of adult patients from our severe asthma clinic who had previously undergone similar testing.

Of 203 patients with ETA who attended the emergency department on 21/22 November 2016, 145 were adults, of whom 31 (21%) attended for follow-up and underwent full assessment by our census date of 22 June 2017. The other patients declined an appointment, failed to attend, or have not yet completed full testing. The demographic characteristics (age, sex) of attendees and non-attendees were similar.

The ETA group had better lung function, fewer current asthma symptoms, and higher levels of sensitisation to rye grass than the severe asthma group (Box). Notably, most ETA patients had a very high RAST result for rye grass (≥ 17.5 kIU/L). Levels of fungal and dust mite sensitisation in the two groups did not differ significantly. The use of inhaled corticosteroids with long acting β-agonists and omalizumab was more frequent in the severe asthma group. Despite their reduced lung function, none of the severe asthma group attended the emergency department or was admitted to hospital during the thunderstorm event.

These results suggest that rye grass pollen was the principal allergen for patients who presented to hospital with ETA. An earlier community study of allergic rhinitis found that a high level RAST result for grass pollen (17.5 kIU/L or more) was associated with a 50-fold relative risk (compared with non-allergic controls) of rhinitis and asthma symptoms when exposed to grass pollen.2 Combined with our findings, this suggests that a high level positive RAST result for rye grass may be useful for predicting the likelihood of risk of ETA in individuals with allergic rhinitis, with or without asthma.

Omalizumab and inhaled corticosteroids attenuate early and late asthmatic responses to allergen challenge,3 and inhaled corticosteroids alleviate ETA.4 We also found that our patients with severe asthma, 70% of whom were sensitised to rye grass, appear to have been protected from ETA by current asthma preventer medications. Because of our small sample sizes, our findings must naturally be interpreted with caution.