Ragweed allergy in northern Italy: are patterns of sensitization changing?

BACKGROUND: Previous surveys performed in this area showed that the age at onset of ragweed allergy in monosensitized subjects is about 35.
OBJECTIVE: To detect whether a reduction in the mean age of ragweed sensitization in the area of Milan has taken place after the last survey.
METHODS: All patients developing clinical ragweed pollen allergy in the years 2007-2010 and monosensitized to this allergen seen were included. 30 randomly selected subjects already sensitized to at least one other allergen source among grass, pellitory, or mite who developed ragweed allergy during the same period served as controls.
RESULTS: The 137 patients showed a median age at onset of ragweed allergy of 36-40 years in the years 2007-2010 with no tendency to reduction. About 10% of patients were < 20 years old in 3 of the 4 study years. 15% of patients were > 50 years old at onset, and 3 of them were > 70. In the control group the mean age at onset of ragweed allergy was 31,6 years (median 32,5 years; range 10-60; p < 0.001 vs patients).
CONCLUSION: In this area monosensitization to ragweed occurs steadily at an adult age. In already allergic subjects it occurs at a younger age. The age at onset of allergy to one specific airborne allergen source seems to depend on several variables, including exposure duration, atopic status, and specific features of the allergen.