Epidemic asthma and the role of the fungal mold Alternaria alternata.

Background: After July 29, 2002, an epidemic of asthma admissions was associated with a thunderstorm in the United Kingdom.
Objective: We sought to study the cause of epidemics of asthma associated with thunderstorms.
Methods: We performed a case-control study of 26 patients presenting to Cambridge University Hospital with asthma after the thunderstorm. Control subjects were 31 patients with summer seasonal asthma. Subjects underwent skin tests and specific IgE serology to inhaled aeroallergens. Meteorologic and aerobiologic data correlated with asthma admissions were analyzed.
Results: Twenty-three of 26 cases had IgE sensitization to Alternaria species. Eleven of 31 control subjects gave a history of asthma exacerbation during thunderstorms. Ten of these 11 control subjects were sensitive to Alternaria species on skin testing, but Alternaria species sensitivity was only identified in 4 of the 20 remaining control subjects who did not report thunderstorm-related asthma symptoms. The odds ratio of having epidemic thunderstorm-related asthma if sensitive to Alternaria species was 9.31 (95% CI, 2.305-37.601; P = .0008) and 63.966 (95% CI, 3.577-1143.9; P < .0001) if sensitive to Alternaria species, Cladosporium species, or both. Poisson regression analysis showed that counts of broken Alternaria species and Didymella and Cladosporium species were significantly correlated with each other and with asthma admissions. The thunderstorm was associated with increased levels of Alternaria, Cladosporium, and Didymella species.
Conclusions: Alternaria alternata sensitivity is a compelling predictor of epidemic asthma in patients with seasonal asthma and grass pollen allergy and is likely to be the important factor in thunderstorm-related asthma.
Clinical Implications: Alternaria species sensitization in asthmatic subjects with grass pollen sensitivity predicts susceptibility to thunderstorm-associated asthma.