Wheezing in relation to atopy and environmental factors in Estonian and Swedish schoolchildren

Background The prevalence of asthma and allergic diseases is significantly lower in post socialist Eastern Europe than in Western industrialized countries. The reason for this difference is largely unknown. Different types of childhood wheezing could be related to different risk factors. Objective To compare the prevalence of respiratory symptoms, asthma and atopic diseases among Estonian and Swedish schoolchildren and to evaluate characteristics for wheezing in the two countries. Methods In a prevalence study, population-based random samples of 10-11-year-old schoolchildren in Tallinn (n = 979), Estonia and in Linkoping (n = 911) and Ostersund (n = 1197), Sweden were studied by a parental questionnaire and skin prick tests (SPT). All 275 children with wheeze in the past 12 months and 710 randomly selected controls within the original cohorts were invited to a case-control study involving a parental questionnaire, examination for flexural dermatitis and bronchial challenge with hypertonic saline. The study adhered to the International Study of Asthma and Allergies in Childhood (ISAAC) Phase II protocol. Results The prevalence of current wheezing was similar (8-10%) in the three centres, while diagnosed asthma and atopic symptoms were more common in Sweden and cold-related respiratory symptoms were more prevalent in Estonia. Frequent wheezing was more common in Sweden than in Estonia (but significantly so only in Ostersund). Wheezing children in Sweden had a high rate of positive SPT (49% in Linkoping and 58% in Ostersund) bronchial hyper-responsiveness (BHR) (48% in Linkoping and Ostersund) and anti-asthmatic treatment (63% in Linkoping and 81% in Ostersund). In Estonia, the proportion of wheezing children with positive SPT, BHR and anti-asthmatic treatment was only 26%, 13% and 17%, respectively. Domestic crowding was inversely related to wheezing in one of the study areas (Ostersund). The mean baseline forced expiratory volume in one second (FEV1) was higher in Estonia than in Sweden, both in wheezing and non-wheezing children. Conclusions Our study suggested that although wheezing symptoms were equally common in Estonia and Sweden, they were less severe in Estonia. More frequent symptoms and a high rate of atopy, BHR and anti-asthmatic medication characterized wheezing children in Sweden. In contrasts BHR, atopy and medication were uncommon among wheezing children in Estonia.