Dales et al. 2003. Six years of emergency room visits for asthma were analyzed to determine the effects of thunderstorms on asthma. Daily hospital admissions for asthma increased 15% on days with thunderstorms. Total spores, ascospores and Cladosporium spores also increased during thunderstorms and were associated with increases in asthma. The authors conclude that a relationship exists between thunderstorms and asthma and suggests that increases in fungal spores are the factors responsible.