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The Perfect Storm for Asthma:
Epidemic asthma and the role of the fungal mold Alternaria alternata
ThomasB. Pulimood, MBBS, MRCPa, JulieM. Corden, BScb, Clare Bryden, MA, MSc, FRMetSc, Linda Sharples, PhDd, ShuaibM. Nasser, MBBS, MD, FRCPa
Many of us have been perplexed by the asthmatic patient whose symptoms flare when foul weather rolls in, sometimes resulting in Emergency Department visits. In the September 2007 issue of the Journal of Allergy and Clinical Immunology, Pulimood et al have sought to explore the cause of epidemic asthma associated with thunderstorms with a case-control study of patients presenting to Cambridge University Hospital with asthma after a storm in late July 2002, when grass pollen levels were on the wane but fungal spores were spiking.
It had previously been reported from Canada that a strong association between emergency visits for asthma and thunderstorms couldn't be explained by grass pollen counts. A review of Mayo Clinic records had revealed that exposure to airborne Alternaria, a mold fungus, was a risk factor for respiratory arrest in children and young adults with asthma. So how is it that the occasion of a thunderstorm presented a "perfect storm" of circumstances to set the stage for an asthma epidemic?
The authors looked at 26 cases of admission for asthma with 31 summer seasonal asthmatics as controls. At the time there was a rise in fungal spore levels that overlapped the end of grass pollen season. This uncommon situation did not give grass-allergic asthmatics who were also allergic to mold spores sufficient time to recover from their pollen-induced bronchial hyperresponsiveness. It is surmised that although grass sensitivity is not an absolute prerequisite for thunderstorm-related asthma, it acts as a cofactor in patients with hay fever and Alternaria allergy by lowering the threshold at which severe acute asthma occurs. Scientists at the California Institute of Technology have proposed a model explaining how a mature thunderstorm may suck up mold spores into the high humidity of the cloud base, break them up into small respirable fragments and then blow these down and out along the ground level in dry cold outflows that can extend 5 km ahead of the rainfall.
These observations having been made, we are left with the question of what can be done. Possible solutions for investigation are preventive therapy with high-dose inhaled corticosteroid or specific immunotherapy to Alternaria prevent these potentially life-threatening attacks of asthma.
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