What lies behind the rare phenomenon of "thunderstorm asthma"

On a single day, 3,365 people sought treatment at hospital emergency departments for acute respiratory complaints. That was almost seven times the number of such cases on "normal" days. As the German "Pharmazeutische Zeitung" reported, 476 of the patients had to be admitted as inpatients — ten times the usual frequency.

The Melbourne 2016 case

According to the Allergieinformationsdienst, the phenomenon has characteristic features: "The severe allergic symptoms occur about 20 to 30 minutes after the start of a thunderstorm." Pollen from grasses as well as fungal spores are especially stirred up in greater quantities in the run-up to a thunderstorm. During the storm, they swell osmotically due to electrostatic charging and high humidity and burst open.

"The allergy-triggering components of the pollen and spores are hurled into the surrounding air and then transported quickly and in large quantities to ground level by strong downdrafts," according to the experts' explanation of the phenomenon surrounding thunderstorms that are often longed for after sultry hot days. Small respirable particles are generally more prevalent in the air during higher atmospheric turbulence, but during a thunderstorm many coarser particles from soil material, bacteria, or mold spores are additionally present.

Who is particularly at risk?

Those affected are not only patients with known bronchial asthma, but also those with other respiratory allergies such as allergic rhinitis. In fact, even more TSA patients have pre-existing allergic rhinitis than asthma. Even individuals who under ordinary conditions have only mild hay fever symptoms can develop TSA, as reported by the German Apothekerzeitung. In people without a prior asthma diagnosis, it is then a case of previously undetected asthma that, for the first time, produces symptoms due to the heavy burden.

For particularly at-risk asthma patients, experts recommend taking medication preventively when a thunderstorm is approaching. Often these are corticosteroid sprays for inhalation and, in acute cases, medications that widen the bronchi. People with severe allergic asthma or hay fever should preferably stay indoors during a thunderstorm.

Recommendations for protection

If staying outdoors cannot be avoided, the German Bundesverband der Pneumologen advises protecting the airways by having those affected inhale through the nose over a cloth and exhale through the mouth without a cloth. In the long term, specific immunotherapy (hyposensitization) can also protect those affected from "thunderstorm asthma."

Allergic asthma attacks or symptoms of allergic rhinitis can occur particularly intensely in people with allergies about half an hour after the start of a thunderstorm, the Munich expert noted. "Thunderstorm asthma" has characteristic features that distinguish it from ordinary pollen exposure — above all, the sudden, mass occurrence of severe symptoms.