The incidence and prevalence of asthma are increasing worldwide making it a global health concern (1). The International Study of Asthma and Allergy in Childhood (ISAAC) reported major geographic variations in the prevalence of asthma in more than 50 countries (2).
Both environmental and genetic factors are thought to influence the prevalence and severity of asthma. Environmental factors may include viral infections (3, 4), allergen sensitization (5), air pollution (6, 7), and inner-city habitat (8). As to genetic factors, similar to hypertension and diabetes mellitus, the inheritance pattern of asthma is complex and cannot be characterized by a single gene. Moreover, varying disease-modifying genes have been linked to asthma in different populations and geographic zones (9–11). Studying the effect of immigration on the prevalence of asthma may help to identify the reasons for the geographic variations and the effects of the environmental and genetic factors on this disease. Immigration involves exposure to new allergens and pollutants and socioeconomic issues such as changes in living conditions and availability of medical services. It has been found that the prevalence of asthma and allergy is relatively low in developing compared with industrialized countries (2, 12, 13). Recently, it has been shown that immigration from developing to industrialized countries increases the risk of having asthma and allergy (14–23). Several studies have also demonstrated a possible correlation between duration of residency in the new country and increased risk for developing asthma and allergy (15, 18–20). Evidence also exists suggesting that the risk of developing asthma increases even within months after immigration (19). Although all these studies have demonstrated similar trends, several limitations need to be considered. First, most studies were held on relatively small populations of both immigrants and controls. Second, given that the diagnosis of asthma was mainly based on self-reported symptoms without objective confirmation of the diagnosis, nonasthmatic transient wheezing or other respiratory diseases could have been mistaken for asthma. Finally, there were insufficient data regarding the possible correlation between duration of residency in the new country and the risk for developing asthma.
Two major factors make the Israeli population ideal for evaluating the effect of immigration on the prevalence of asthma. For many years, Israel has been a destination for Jewish immigrants from all over the world. During the last 20 years more than one million immigrants arrived in Israel, most of them from the FSU, others from other parts of Europe, North America and Ethiopia. Furthermore, at the age of 17, most Israeli adolescents undergo a complete medical evaluation as part of a routine health assessment before mandatory military service. This provides a unique opportunity to study the effects of immigration on the prevalence of asthma in a large group of Israeli adolescents.
Accordingly, we aimed to study the effect of age at immigration and the country of birth on the prevalence of asthma in 17 years old Israeli adolescents.