To the Editor:
I read with interest the article by Tobias et al. 1. Firstly, I would like to state my doubts on the validity and relevance of using the umbrella term “immigrants” in reference to people from various countries of the world who settle in developed countries.
Most of the time, leaving one's home country is not a deliberate action. The main initiatives are related to economical and political reasons. Those who immigrate for economical reasons usually use legal routes. The legal process makes it obligatory to have a health check and does not permit diseased individuals to migrate. This obligation does not hold true for the immigrants who leave their countries for political reasons. Political immigrants are however, still expected to have a relatively better health status than the general population to enable them to escape the legal barriers and leave their country. The observation in Turkish workers and their families in Europe may give the main supporting evidence for this view. The prevalence of asthma, atopy and bronchial reactivity was even lower in second-generation Turkish children when compared with children of native German and Swedish populations 2. Immunoprotection is probably a multifactorial phenomenon that presumably includes bacille Calmette-Guérin (BCG) vaccination status, diet, breastfeeding, tobacco consumption, type of fuel used at home, infections in the early life (due to bacteria, viruses, and parasites), and genetic factors. In addition, I believe that a health-selection factor (similar to the “healthy worker effect”) is involved in immigrants.
Different fates may be anticipated for the immigrants in their new countries. Frequently, they work in jobs that native people do not want to do. While a minority adapt to the new society (language, diet, hobbies, etc.) without any problems, most of the others suffer great difficulties in adapting. The latter “dive in their own ghettos”, carry on their own traditions, consume their special food, try to establish their own business if they can, and visit their home town whenever possible. These two groups of immigrants, who share the same environment but have different levels of adaptation, could be compared to Germany before the unification.
Language has been cited as an outstanding problem in the epidemiological studies of asthma. “Wheezing” has been regarded as an awkward word, even in English speaking countries. As far as I know, “dyspnoea” is used as a diagnostic equivalent in many countries and asthma is a fearful “foreign phrase” for society. Thus, clinicians in various countries of the world, have used alternative terms, such as allergic bronchitis, bronchitis and spastic bronchitis. In some African languages, there is no synonym for asthma.
It has been reported that prevalence of asthma is increasing in developed countries, whereas the status in less developed countries is not well known. For example, there was no significant difference in the prevalence of asthma in a series of cross-sectional studies conducted 5 yrs apart in Ankara, Turkey 4. This is an important factor for the prevalence of asthma and allergic diseases in immigrants from less developed countries.
Another important factor is the duration immigrants stay in a new country. In Uppsala, Sweden, total immunoglobulin (Ig)-E levels of nonatopic immigrants from various parts of the world were higher than that of the nonatopic-, age- and sex-matched native Swedish people 5. Total IgE levels of the immigrants from various parts of the world showed notable differences. This difference in the level of total IgE, which is used as a rudimentary marker of allergy and asthma in epidemiological studies, is likely to disappear after living in the new country for ≥10.5 yrs 5. During the same period, allergen spectra in skin testing of atopic immigrants resembles that of the native population 5. Another study conducted in Turkish immigrants in Sweden supported this finding 6. In the atopic Turkish immigrants, sensitivity to birch, cat, and dog increased in parallel with the changes in their living conditions. We can therefore say that immigrants gain immunological adaptation to the new environment within a mean period of 10 yrs (time effect). Thus, investigations of asthma in immigrants should also assess the duration of stay in the new country.
In my opinion, studies conducted on immigrants should take into account the differences that exist within the immigrant populations. The problems of adaptation to the new society and duration of stay in the new country should also be carefully addressed. This is a promising field, as prospective studies conducted on immigrants could provide valuable information about protection from asthma and allergic diseases.
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