The association between asthma and rhinitis is stable over time despite diverging trends in prevalence

Background: Despite the well-known association between asthma and rhinitis, in Swedish adults the prevalence of rhinitis rose from 22% to 31% between 1990 and 2008 while asthma prevalence was unchanged. We tested whether the association of rhinitis with asthma was stable over time using the same population-based databases. Methods: Two surveys of adults (20-44 years) living in three regions of Sweden, carried out in 1990 (n = 8982) and 2008 (n = 9156) were compared. Identical questions regarding respiratory symptoms, asthma and rhinitis were used. Asthmatic wheeze: Wheeze with breathlessness apart from colds. Current asthma: Asthma attacks and/or asthma medication use. Results: Subjects with rhinitis had level time trends in asthmatic wheeze, current asthma and most nocturnal respiratory symptoms between 1990 and 2008, adjusted for age, sex, area and smoking. Any wheeze however decreased slightly. In never-smokers asthma symptoms were similarly associated with rhinitis in 1990 and 2008: any wheeze OR 4.0 vs. 4.4 (p = 0.339); asthmatic wheeze OR 6.0 vs. 5.9 (p = 0.937); and current asthma OR 9.6 vs. 7.7 (p = 0.213). In the whole population there were decreases in the asthma symptoms most closely associated to smoking, which decreased by half 1990-2008. Conversely current asthma, which was strongly associated with rhinitis and not with smoking, increased (p < 0.001). Conclusions: The association of rhinitis with asthma was stable between 1990 and 2008. The pattern in the time trends of asthma outcomes strongly suggests that decreased smoking counterbalanced the driving effect of increased rhinitis on asthma prevalence. The findings illustrate the public health benefits of decreased smoking.