Injection immunotherapy with different airborne allergens did not prevent de novo Sensitization to ragweed and birch pollen north of Milan

Background: Previous studies suggest that allergen-specific immunotherapy ( SIT) with a single allergen may prevent sensitization to other airborne allergens. Objective: To assess the effectiveness of injection SIT in preventing sensitization to birch and ragweed pollen north of Milan, a geographical area that was recently colonized by these two airborne allergens. Methods: 691 adult patients monosensitized to grass (n = 342), pellitory ( n = 76), ragweed ( n = 66), birch ( n = 112), and house dust mite ( n = 95) were studied. 284 (41%) of them received injection SIT as part of routine outpatient care; the remaining 407 (59%) not submitted to SIT, served as controls. All patients underwent follow-up visits after no less than 2 years in order to detect possible new sensitization to birch and/or ragweed. Results: 227 (33%) patients became sensitized to birch and/or ragweed pollen during the follow-up period. Surprisingly, the prevalence of new sensitizations was significantly higher among subjects receiving SIT (132/284; 46%) than among those not receiving SIT (95/407; 23%; p < 0.001). 27 subjects developed new sensitization to birch and/or ragweed pollen while undergoing SIT. These findings were consistent in all subgroups with different airborne allergies. Conclusion: In this study, injection SIT did not exert any preventive effect against denovo sensitization to the two novel airborne allergens, birch and ragweed pollen, in adult monosensitized patients. Copyright (C) 2004 S. Karger AG, Basel.