Eleven‐year trends in walnut‐induced anaphylaxis in children in Japan: A multicenter retrospective study

Abstract Background In recent years, the prevalence of walnut allergies has been increasing worldwide; however, the trends and clinical characteristics of walnut‐induced anaphylaxis remain unclear. Herein, we evaluated the changes in the incidence of walnut‐induced anaphylaxis and assessed patient characteristics and symptoms. Methods This retrospective study enrolled patients who visited the pediatric emergency departments (ED) at three institutions due to food‐induced anaphylaxis between 2011 and 2021 in Japan. Changes in the proportions of each causative food over 11 years were evaluated using the Cochran–Armitage trend test. Patient characteristics and detailed symptoms were compared between patients with anaphylaxis due to walnuts (walnut group) and other foods (other food group). Results In total, 904 patients presented to the ED with food‐induced anaphylaxis. Among the causative foods, the incidence of walnut‐induced allergies increased from 3.2% in 2011 to 26.1% in 2021 ( p < .0001), while no significant changes were observed for other foods. Comparing 80 patients in the walnut group with 824 patients in the other food group, the median ages were 3.9 years in both groups ( p = .42). The proportion of patients previously diagnosed with allergy to the causative food was lower in the walnut group (28.8%) than in the other food group (47.4%; p = .006). Gastrointestinal symptoms were more common in the walnut group (72.5%) than in the other food group (55.9%; p = .004). Conclusion Since the late 2010s, the incidence of walnut‐induced anaphylaxis has rapidly increased in Japan, particularly among young children with first‐episode reactions.