Greater severity of new onset asthma in allergic subjects who smoke: a 10-year longitudinal study.

Background: Little is known about the association between cigarette smoking and asthma severity. We assessed smoking as a determinant of disease severity and control in a cohort of clinic-referred allergic subjects who developed new onset asthma.

Methods: Allergic rhinitis subjects with no asthma (n = 371) were followed-up for 10 years and routinely examined for asthma diagnosis. In those who developed asthma (n = 152), clinical severity and levels of asthma control were determined. Among these subjects, 74 (48.7%) were current smokers, 17 (11.2%) former smokers, and 61 (40.1%) never smokers.

Results: When comparing current or past smokers to never smokers they had a higher risk of severe asthma in the univariate analysis, which became non-significant in the multivariate analysis. On the other hand, the categories of pack-years were significantly related to severe asthma in a dose response relationship in both the univariate and multivariate analysis: compared to 0 pack years, those who smoked 1-10 pack-years had an OR(95% CI) of 1.47(0.46-4.68), those who smoked 11-20 pack-years had an OR of 2.85(1.09-7.46) and those who smoked more than 20 pack-years had an OR of 5.59(1.44-21.67) to develop more severe asthma. Smokers with asthma were also more likely to have uncontrolled disease. A significant dose-response relationship was observed for pack-years and uncontrolled asthma. Compared to 0 pack years, those who smoked 1-10 pack-years had an OR of 5.51(1.73-17.54) and those who smoked more than 10 pack-years had an OR of 13.38(4.57-39.19) to have uncontrolled asthma.

Conclusions: The current findings support the hypothesis that cigarette smoking is an important predictor of asthma severity and poor asthma control.