Background: Although the occurrence of bronchial asthma is still increasing, the possible factors associated with the development of severe asthma have not been completely determined.
Objective: To measure the incidence of severe asthma and its determinants in outpatients. Aspirin intolerance, house dust mite (HDM) allergy, male sex, age older than 65 years, and duration of asthma exceeding 10 years were investigated as factors potentially related to the severity of asthma.
Methods: The study population included 598 women and 408 men, mean age of 44.59 years (SD +/- 16.45 years), randomly chosen from patients with asthma under follow-up surveillance in an outpatient clinic. Their medical histories were reviewed; spirometry and skin prick tests were performed.
Results: The asthma was diagnosed as intermittent in 35.39%, persistently mild in 33.40%, moderate in 23.76%, and severe in 7.45% of the study cohort. In the patients with atopy, HDM allergy was a significant factor associated with the development of severe asthma [odds ratio (OR) = 5.65]. Of the 1,006 patients, 341 (33.90%) had had asthma for at least 10 years, which was a significant factor in the overall study group (OR = 3.64). We found 95 cases (9.44% of the study group) of aspirin intolerance, including 23 of the 75 patients with severe asthma (30.67%; OR = 5.44). Logistic regression analysis showed that aspirin intolerance was most closely associated with severe asthma (beta = 5.79; P < .001).
Conclusions: The data from this study show that aspirin intolerance, HDM allergy, and asthma duration exceeding 10 years are major factors associated with severe asthma in outpatients.