Allergic patients have more numerous and prolonged respiratory infections than nonallergic subjects.

Allergic disorders are characterized by type 2 helper T cell (Th2)-polarization, thus physiological type 1 helper T cell (Th1)-dependent mechanisms involved in fighting respiratory infections (RI) may be defective. It has previously been reported that allergic children have more numerous and severe RI than nonallergic ones.The aim of the study was to evaluate the number and duration of RI in adult allergic and nonallergic subjects.Six hundred and twenty-four subjects were studied; 202 of them were allergic (i.e. suffering from allergic rhinitis). The number of RI as well as the duration of the disease were recorded for 2 years.Allergic subjects showed a significantly higher rate of RI episodes [adjusted incidence rate ratio (IRR) = 2.16, 95\% confidence interval (CI) 1.94-2.41, P < 0.001] than subjects without allergy. The number of mild RI episodes was slightly higher in allergic subjects (IRR = 1.68, 95\% CI 1.50-1.89, P < 0.001), while the number of severe episodes was markedly higher (IRR = 15.71, 95\% CI 10.35-23.84, P < 0.001) when compared with nonallergic subjects. Moreover, allergic patients showed a longer total duration of RI than nonallergic subjects, with a mean difference of 17.4 days (95\% CI 15.5-19.4, P < 0.001).This study provides evidence that adult allergic patients have more numerous and prolonged RI than nonallergic subjects.