We subtracted the midpoint of these ranges from the subject’s age to estimate the age at immigration and then dichotomized as < 2 years or ≥ 2 years. In order to examine whether the age of immigration affected the odds of food sensitization, we used a variable for length of stay in the US which categorized subjects as having lived in the US for < 1 year, 1-<5 years, 5-<10 years, 10-<15 years, 15-<20 years, or 20-<30 years. The US-born group was then split into those living with a US-born householder (“US-born/non-immigrant household”) and those living with a foreign-born householder (“US-born/immigrant household”). Analyses were first done comparing US-born to foreign-born children and adolescents. Data from the 2010 census support this use, showing that more than 98% of the time a child is a relative of the head of household with whom he/she lives 89% of the time the head of household is a parent( 24). The nativity of head of household was used as a proxy for the parent’s nativity. The main exposures were the nativity of the subject and the subject’s head of household, which were both defined as US-born or foreign-born. Seasonal sensitizations, which were only assessed in subjects at least 6 years of age, were defined as a specific IgE of at least 0.35 kU/L for at least one of: ragweed, rye grass, Bermuda grass, oak, birch, and thistle. pteronyssinus, cat, dog, cockroach, and Alternaria. In addition to the foods mentioned above, specific IgE was measured in all subjects to: D. Because of the difficulty in diagnosing asthma in young children, sensitivity analyses were conducted of asthma outcomes including only those aged 6 and above. We also assessed the relationship between immigration and sensitization to aeroallergens, and to history of health professional’s diagnosis of asthma, hay fever, and eczema. Accordingly, probable food allergy was defined as at least one of the following: If less than 2 years of age, IgE to milk ≥ 5 kU/L, egg ≥ 2 kU/L, or peanut ≥ 14 kU/L, and if at least 2 years of age, IgE to milk ≥ 15 kU/L, egg ≥ 7 kU/L, or peanut ≥ 14 kU/L ( 4). Because no information on clinical reactivity was available, sensitivity analyses were done using food-specific IgE cut-offs that have previously been identified as being indicative of probable food allergy( 4, 22, 23). Allergen specific IgEs were analyzed using the Pharmacia Diagnostics Immunocap 1000 system (Kalamazoo, MI). The main outcome measure was food sensitization, defined by a specific IgE of at least 0.35 kU/L to milk, egg or peanut. Measurement and definition of exposures and outcomes In this study, we sought specifically to investigate whether native and foreign-born residents of the US have different risks of food sensitization, whether the risk of food sensitization differs by immigration status of a child’s parent, and whether the timing of immigration affects the risk of food and aeroallergen sensitization. As a country of immigrants representing many generations, the US offers a unique opportunity to examine multi-generational effects of immigration on the risk of allergic disease. In order to examine the effects of immigration to the US on the risk of food sensitization, we examined a large, nationally representative sample of children and adolescents living in the US. In our clinical practice, we have noted a disproportionate rate of food allergy among first-generation Americans, and thus hypothesized that personal and parental nativity may affect the risk of food sensitization differently.
However, the relationship between immigration and food allergy has only rarely been studied( 5, 20, 21), even though the pathophysiologic mechanisms of food allergy may be distinct from other allergic disorders. Despite the fact that immigrants to developed countries tend to have lower rates of most sensitizations than native born populations, ethnic minorities in developed countries tend to have high rates of allergic sensitization( 4, 14, 18), and some data indicate that children of immigrants are at particular risk for various atopic diseases( 14, 19, 20). Previous studies of asthma have generally shown that immigrants to developed countries have lower rates of asthma and allergic sensitization than native born populations of the same( 5- 15) and different ethnicities( 16, 17). Large discrepancies in the rates of food allergy are found by geography( 2) and ethnicity( 1, 3, 4). Food allergy is a problem of complex etiology that appears to be rapidly increasing in prevalence( 1).
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