Changes over 13 years in skin reactivity to histamine in cohorts of children aged 9-13 years

Background: Several studies report substantial differences in the prevalenc e of skin test reactivity to allergens in children from adjacent geographic areas; others report an increased prevalence over time. To find out whethe r these differences depend on variations in skin reactivity to histamine, w e determined the time trend of histamine wheal sizes in successive cohorts of unselected children living in the same area (Viterbo, Italy). Methods: We conducted three epidemiologic surveys, each including children aged 9 and 13 years. The 1983-7 study investigated 170 children (150 were t ested twice); the 1992 study, 158 children; and the 1996 study, 208 childre n. Results: In both age groups, the mean diameter of the wheal induced by hist amine skin prick tests (10 mg/ml) increased significantly over time (9-year -olds: 3.25 mm in 1983, 4.68 in 1992, and 5.89 in 1996; 13-year-olds: 3.89 mm in 1987, 5.18 in 1992, and 6.50 in 1996) (P < 0.001 between subsequent s tudies). The distribution of the wheal diameters for both ages showed a tre nd to a right shift in the three successive studies (P < 0.001). The dose-r esponse curves for three histamine concentrations (0.2, 1, and 10 mg/ml) ha d significantly steeper slopes in 1996 than in 1983-7 (P < 0.001). Conclusions: The marked time-related increase in the size of the histamine wheals could help to explain the trend toward an increased prevalence of po sitive allergen skin test reactions reported during the past years. The cau ses of increased skin reactivity to histamine remain conjectural.