Prevalence of birch pollinosis and oral allergy syndrome in the general population of Hokkaido, Japan

Objective Birch pollen is the predominant tree pollen allergen in Hokkaido, Japan, and is frequently associated with oral allergy syndrome (OAS). However, most previous studies have been hospital-based, and population-level data remain limited. Methods We conducted a cross-sectional questionnaire survey of residents of Hokkaido recruited through 10 medical institutions and their family members. Data were collected on physician-diagnosed birch pollinosis, oral allergy symptoms after food ingestion, demographic factors, residential area, and comorbid allergic diseases. Associations were evaluated using chi-square tests, odds ratios (OR) with 95% confidence intervals (CI), and multivariate logistic regression analyses. Results A total of 3615 residents were included. The prevalence of physician-diagnosed birch pollinosis was 15.21%, higher than that of other pollen allergies. In multivariate analysis, residential area was an independent determinant of birch pollinosis, with significantly higher odds in northern, central, and eastern Hokkaido than in southern Hokkaido. Female sex, age, perennial allergic rhinitis and food allergy were also independently associated with birch pollinosis. Oral allergy symptoms were reported by 22.41% of participants and occurred in 66.55% of individuals with birch pollinosis. In the multivariate model for oral allergy symptoms, birch pollinosis was a strong independent factor, with additional associations observed for female sex, age, perennial allergic rhinitis and atopic dermatitis. Conclusions Birch pollinosis and OAS are highly prevalent in Hokkaido. Oral allergy symptoms are strongly linked to birch pollinosis, supporting OAS as a characteristic clinical manifestation of birch pollen sensitization in birch-endemic regions.