Birch Rust Spore Exposure and Upper Airway Symptom Dynamics in a Subarctic Region: Indications for a Novel Seasonal Allergen

BACKGROUND: Airway allergies affect 20%-30% of the global population, with pollen and fungal spores representing major environmental triggers. Although fungal spores are far more abundant than pollen, their allergenic role-particularly from phytopathogenic rust fungi such as birch rust (BR)-remains poorly understood. In Northern Norway, where seasonal dispersal of BR spores occurs with minimal overlap from other aeroallergen exposures, we investigated their potential contribution to autumnal airway symptoms by linking spore distribution with clinical outcomes.

METHODS: In this prospective study, 160 patients and 94 controls were followed during BR season (Aug-Oct) and out of season (Jan-Feb). Participants reported allergic rhinitis, conjunctivitis, and/or asthma. Symptom scores (Visual Analogue Scale), nasal airflow (Peak Nasal Inspiratory Flow), and lung function (spirometry) were recorded, alongside daily BR spore counts from three monitoring sites.

RESULTS: During BR season, patients showed significantly higher symptom severity (VAS difference 1.58, p < 0.01) and lower PNIF values (-12.2 L/min, p = 0.01) versus controls. Seasonal increases in symptoms were observed (1.70, p < 0.001), and anti-allergic medication use was more frequent in patients (62.5% of patients vs. 1.1% of controls (p < 0.001). Symptom worsening was associated with reported proximity to birch forests (regression coefficient 0.46, p < 0.01, R 2 = 0.48).

CONCLUSIONS: BR spore exposure was associated with increased autumnal airway symptoms, suggesting that BR may represent an underrecognized trigger. These findings highlight the need for further research, including allergen-specific testing and dispersal modelling, to clarify their clinical relevance.

TRIAL REGISTRATION: This study is registered at ClinicalTrials.gov (identifier: NCT05661812).