Allergen immunotherapy effectively reduces the risk of exacerbations and lower respiratory tract infections in both seasonal and perennial allergic asthma: a nationwide epidemiological study

Background Allergic asthma is associated with increased risk of respiratory tract infections and exacerbations. It remains unclear whether this susceptibility is conditioned by seasonal or by perennial allergy. Aim To investigate perennial allergy compared with seasonal allergy as a risk factor for lower respiratory tract infections and exacerbations in asthma and whether this risk can be reduced by allergen immunotherapy (AIT). Methodology This is a prospective register-based nationwide study of 18–44-year-olds treated with AIT during 1995–2014. Based on the type of AIT and use of anti-asthmatic drugs, patients were subdivided into two groups: perennial allergic asthma (PAA) versus seasonal allergic asthma (SAA). Data on antibiotics against lower respiratory tract infections (LRTI) and oral corticosteroids for exacerbations were analysed before starting AIT (baseline) and 3 years after completing AIT (follow-up). Results We identified 2688 patients with asthma treated with AIT, of whom 1249 had PAA and 1439 had SAA. At baseline, patients with SAA had more exacerbations (23.8% versus 16.5%, p≤0.001), but there were no differences in LRTI. During the 3-year follow-up, we observed a highly significant reduction of exacerbations with an average decrease of 57% in PAA and 74% in SAA. In addition, we observed a significant reduction of LRTI in both PAA and SAA: 17% and 20% decrease, respectively. Conclusion AIT effectively reduced the risk of exacerbations and lower respiratory tract infections in both seasonal and perennial allergic asthma. Perennial allergy is seemingly not a stronger risk factor for respiratory infections and exacerbations than seasonal allergy.