Objective: The aim of this study was to explore the role of rhinoconjunctivitis (RC), taking into account atopy and the level of bronchial responsiveness to methacholine, on the incidence of respiratory symptoms and in the development and/or worsening of asthma.
Methods: We examined data from a prospective study in 769 students starting exposure to high-molecular-weight occupational allergens and who were serially followed for up to 44 months.
Results: The presence of RC symptoms at baseline was significantly associated with an increased risk of developing shortness of breath and wheezing in atopic subjects regardless of PC20 level and in subjects with a PC20 ≤ 32 mg/ml regardless of atopic status. RC symptoms were significantly associated with the development of exercise-induced respiratory symptoms. Multivariate analyses indicated that having a measurable PC20 was significantly associated with the incidence of all respiratory symptoms studied, whereas baseline seasonal RC was associated only with incident exercise-induced respiratory symptoms; atopy played a minimal role, and only through an interaction with seasonal RC.
Conclusion: Of the three potential factors for the development of respiratory symptoms that we considered, i.e. RC symptoms, having a measurable PC20 and atopy, having a measurable PC20 is the most significant one.