Effect of natural allergen exposure on non-specific bronchial reactivity in asthmatic farmers

The aim of the study was to assess the seasonal variability of non-specific bronchial reactivity (NSBR) evaluated with methacholine in asthmatic farme rs allergic to pollens. Twenty farmers (16 male and four female) with aller gy to pollens, e.g. 'Graminae' and 'Parietaria: entered the study, None of the patients had been previously treated with specific immunotherapy. Patie nts underwent a methacholine challenge at the first visit and then in the s ubsequent seasons. Four groups of tests were obtained according to the peri od when the challenge was performed. Group 1: challenges performed in Decem ber, January and February; group 2 in March, April and May; group 3 in June , July and August; group 4 in September, October and November. PD20 values were expressed as the natural logarithm of the cumulative dose of methachol ine causing at least a 20% fall in FEV1. Bronchial hyperreactivity was high est in summer, followed by spring and autumn; in winter it was much lower. Multiple group analysis (ANOVA) showed statistically significant difference s between the groups (P < 0.01). When th:e groups were compared individuall y, statistically significant differences existed only between group 1 (wint er) and each of the other groups, respectively 2 (spring) (P = 0.02), 3 (su mmer) (P = 0.004) and 4 (autumn) (P = 0.02). The results underlined the imp ortance of allergic inflammation in determining changes in NSBR. In the reg ion where the study was carried out (central Italy), the grass and Parietar ia pollination lasts from March to November. Therefore, farmers had a progr essive increase in NSBR from spring to summer and a decrease in fall as a c onsequence of the varying pollen concentration in different seasons. The le vel of allergen exposure is, in fact, the main factor that determines the s everity of bronchial inflammation, thus affecting NSBR. <(c)> 2001 Elsevier Science B.V. All rights reserved.