The effect of selected risk factors, including the mode of delivery, on the development of allergic rhinitis and bronchial asthma

Introduction
Cesarean section affects the process of colonization by bacteria transferred from the mother’s skin and hospital bacteria, which in turn contributes to development of allergic conditions.

Aim
To assess selected risk factors, including the mode of delivery, parity, and the role of genetic factors for the development of allergic rhinitis and bronchial asthma.

Material and methods
The study was conducted in 18,617 respondents aged 6–7, 13–14, and 20–44 years who completed the ECRHS II and ISSAC questionnaires. Thirty percent of the study population underwent complementary assessments in the form of skin-prick tests, serum IgE levels, lung function tests, and peak nasal inspiratory flow (PNIF). The study is a part of the Epidemiology of Allergic Disorders in Poland (ECAP) study conducted in 8 areas in Poland (Warsaw, Lublin, Bialystok, Gdansk, Poznan, Wroclaw, Katowice, Krakow, and two rural areas – Zamosc and Krasnystaw counties).

Results
Respondents diagnosed with allergic rhinitis were at a significantly higher risk of inheriting the allergic condition if their mother (OR = 2.17; 95% CI: 1.98–2.39, p = 2.00 × 10^–16) or father (OR = 2.20; 95% CI: 1.96–2.47; p = 2.00 × 10^–16) suffers from this allergy. Conversely, in the group diagnosed with bronchial asthma, the highest risk of an inherited allergy was observed in situations where maternal (OR = 2.00; 95% CI: 1.57–2.55; p = 1.69 × 10^–5) or paternal (OR = 1.94; 95% CI: 1.42–2.66; p = 3.61 × 10^–5) grandparent was affected. Moreover, the risk of developing allergic rhinitis depended on the mode of delivery: i.e. it was higher for a Cesarean section (OR = 1.20; 95% CI: 1.01–1.43; p = 0.04) than vaginal delivery (OR = 0.88; 95% CI: 0.78–0.99; p = 0.03). The higher the number of siblings, the lower the risk of allergic rhinitis.

Conclusions
Allergy risk factors, especially those predisposing to allergic rhinitis, include not only genetic factors but also the mode of delivery: vaginal delivery or Cesarean section.