Abstract

Background: Children whose 11th fetal week falls in pollen season (spring) reportedly have an increased risk of sensitization to food allergens. No such finding has been reported for pet allergens. Objective: The aim of the study was to (i) evaluate the incidence of pet (dog and cat) sensitization according to the season of the 11th fetal week and (ii) whether the association between pet exposure and respective sensitization is modified by the coincidence of the 11th fetal week with pollen season. Methods: The study population comprised all children (born between 2001 and 2006) in the province of South Karelia, Finland (N = 5920). Their data of immunoglobulin E antibodies and skin prick tests to pet allergens (N = 538) were collected from patient records and linked with questionnaire data on pet exposure. Results: The seasonal incidence peak of cat sensitization was observed in children whose 11th fetal week occurred in June (7.4%) and that of dog sensitization in April (3.8%) and June (4.7%). The relative rate (RR) for cat sensitization was 2.92 (95% CI 1.40‐6.08) in children with cat exposure alone, 8.53 (4.07‐17.86) in children with cat and fetal pollen exposures and 0.61 (0.20‐1.83) in children exposed to pollen alone, compared with children without these exposures. The respective RRs for dog sensitization were 2.17 (1.13‐4.19), 4.40 (2.19‐8.83) and 1.65 (0.77‐3.53). Conclusions and clinical relevance: Coincidence of the first fetal trimester with pollen season strengthens the association between pet exposure and respective sensitization. Pollen exposure at early pregnancy may deviate immune system towards Th2‐type reactivity promoting development of specific allergy in case allergen exposure occurred. Therefore, primary prevention of allergic diseases may need to begin during early pregnancy.