Background: The objectives of this study were to investigate the prevalence of sIgE to galactose-α-1,3-galactose (α-gal) in individuals with acute urticaria or anaphylaxis from different geographical areas of Spain and to evaluate the relevance of demographics and lifestyle as risk factors for this immune response.
Methods: Participants were recruited from allergy departments at 14 Spanish hospitals. Patients aged 18 years or older presenting with urticaria or anaphylaxis were enrolled into one of 2 arms: cases and controls. An interviewer-administered questionnaire collecting demographic data, lifestyle habits, and the presence of cofactors was obtained from each participant. sIgE to α-gal and total IgE were determined using ImmunoCAP. sIgE levels ≥0.35 kU/L were considered a positive result.
Results: The study population comprised 160 cases and 126 controls. The median age was 44 years. The overall prevalence of a positive result of sIgE to α-gal was 15.7%; this was higher in cases (26.3%) than in controls (2.4%). The sIgE anti–α-gal positivity rate ranged from 37.68% (rural) to 15.38% (semiurban), and 7.85% (urban). The rates of positivity were 46.32%, (Northern), 0.72% (Center), and 0% (Mediterranean). A positive result for sIgE to α-gal was associated with a history of tick bites, participation in outdoor activities, pet ownership, and ingestion of mammalian meats or innards before the onset of symptoms. Only alcohol consumption could be implicated as a cofactor.
Conclusion: Sensitization to α-gal in patients with urticaria or anaphylaxis differs considerably between the 3 geographical areas studied and is related to tick bites.

Key words: α-Gal, Risk factors, Epidemiology, Outdoor activities, Tick bites, Cofactors