Occurrence and risk factors of asthma, allergic rhinoconjunctivitis and allergic sensitisation in rural and urban Mongolia

Abstract

Introduction: The prevalence of atopic diseases varies widely throughout the world. The increase in the risk of these types of diseases has been associated with a western lifestyle. The aim of this study was to investigate the role of environment and lifestyle changes on the risk of atopy in Mongolia, a country in transition between nomadic and western lifestyles. Objective: To study the prevalence and risk factors of asthma, allergic rhinoconjunctivitis and allergic sensitisation in Mongolia in areas with different levels of urbanisation: villages, rural towns and Ulaanbaatar city. Materials and Methods: In the screening study, questionnaire data were obtained from 9453 subjects aged 10–60 years. In the clinical study, a subsample of 869 subjects (participation rate 50.0%), enriched with symptomatic subjects, was examined. A detailed questionnaire-based interview, clinical examination, skin-prick tests, spirometry, and bronchodilation tests or methacholine challenge tests were carried out. Asthma, allergic rhinoconjunctivitis and allergic sensitisation were defined by the clinical examination. The results were related to the population level using sampling weights. The prevalence rates were evaluated in the villages, rural towns and Ulaanbaatar city. Multiple logistic regression analysis was used for the investigation of risk factors. Results: The prevalence rate of current asthma was low, 1.1%–2.4%, depending on the study area. The prevalence rate of allergic rhinoconjunctivitis was high in relation to the prevalence rate of asthma, but low compared internationally, 9.3%–18.4%. The prevalence rate of allergic sensitisation was 13.6%–31.0%. The prevalence rates were lowest in the villages. A significant increase was seen in the prevalence rates of allergic rhinoconjunctivitis and allergic sensitisation with increasing exposure to town environment in analyses of current place of residence and also in analyses considering relocation from rural to urban areas. Keeping herd animals did not explain the protective effect of living in a village, but exposure to both herd animals and to dung heating was associated with a reduced risk for allergic sensitisation and allergic rhinoconjunctivitis. Keeping animals was a risk factor for asthma in the city, but not in the rural areas. Conclusions: The prevalence rate of atopic disorders was low in rural Mongolia, but it increased with increasing urbanisation. Moving from a village to a town increased the risk of atopy, but the risk was highest among those living in a town since birth. An environment with exposure to dung heating and herd animals protected against atopy in rural Mongolia, which suggests the importance of exposure to environmental microbes for protection.