Birch-pollen sensitization in an area without atmospheric birch pollens

Objective: To clarify the incidence of individuals with a subclinical allergy to birch pollen and the possible allergic association between birch pollen and other allergens in areas without atmospheric birch pollen. Methods: Birch-pollen-specific immunoglobulin E concentration in sera, together with those for some other inhaled and ingested allergens, was measured in 409 male and 525 female patients (an average age of 58.6 years, born and raised in an area without atmospheric birch pollen) with suspicious nose and/or throat allergies. Concomitantly, types and concentrations of pollen grains in the regional air were examined. Results: Of 934 patients 13.2% showed birch-pollen-specific immunoglobulin E although no birch pollens were observed in the atmospheric air. The rate was relatively low in comparison with those for clinically important inhaled allergens in this area: 35.2% for Japanese cedar pollen, 24.7% for house dust and 23.2% for cypress pollen. Spearman's rank correlation analysis and logistic regression analysis revealed that birch pollen correlated strongly with apple and some foodstuffs commonly ingested by all age groups ( ρ>0.6000, odds ratio>27.191). Conclusions: A considerably large number of patients with a subclinical allergy to birch pollen exist in an area without atmospheric birch pollen. Measurement of specific immunoglobulin E to birch pollen is important even in such areas for screening and diagnosing patients with oral allergy syndrome.