Cross-sensitization profiles of edible nuts in a birch-endemic area

Background: Sensitization to birch pollen causes cross-sensitization to nuts, but rarely leads to clinical nut allergy. The aim was to study sensitizations to nuts in individuals sensitized to birch pollen and examine cross-reactivities between birch and nut species. Methods: All subjects with skin prick tests (SPTs) for birch pollen conducted during 1997-2013 in the Skin and Allergy Hospital in Helsinki (n = 114 572) and their available SPTs for nuts (n = 50 604) were included. Nut sensitizations were analyzed both with and without cosensitization to birch and stratified into age-categories. Cross-reactivities were analyzed with hierarchical clustering. One group of 1589 patients was surveyed for symptoms. Data were gathered also from Lapland to examine sensitizations in an area with less birch-pollen exposure. Results: Of subjects with birch sensitization, 84% were cosensitized to hazelnut, 71% to almond, and 60% to peanut. In a subgroup without birch sensitization, young children (<5 years) were most commonly nut-sensitized (8-40%); and this prevalence decreased in adolescents and further in adults (4-12%). Cashew and pistachio (q = 0.66; P < 0.001) and pecan and walnut (q = 0.65; P < 0.001) correlated the strongest. The majority of nut-sensitized patients (71% hazelnut, 83% almond, 73% peanut) reported no or mild symptoms. Cosensitizations between nuts and birch were similar in Lapland with its lower birch-pollen exposure. Conclusion: Birch-sensitized individuals are frequently cosensitized to hazelnut, almond, and peanut. Among the birch-negatives, prevalences of nut sensitizations decrease from early childhood to adolescence. Cashew and pistachio, and pecan and walnut cross-react the most.