BACKGROUND:
The impact of migration on the risk of anaphylaxis is unknown. We hypothesized that non-Western immigrants have a lower incidence of anaphylaxis compared to Danish-born. We investigated variations in hospital attendance for anaphylaxis between immigrants and Danish-born including time- and age- trends.

METHODS:
A register-based, historical prospective cohort design. Refugees or family reunified immigrants (n=127,250) who, between January 1,1994 and December 31, 2010, obtained residency permits in Denmark were included and matched in a 1:6 ratio on age and sex with Danish-born individuals (n=740,600). Personal identification numbers were cross-linked to the Danish National Patient Registry identifying all first-time hospital attendances for anaphylaxis from January 1,1994 and December 31, 2010. Incidence rate ratios were estimated stratified for sex and region of birth, adjusting for age using a Cox regression model including the influence of duration of residence and age when residence was obtained.

RESULTS:
In total 1,053 hospital attendances for anaphylaxis were identified: 89 among non-Western immigrants, 9 among Western immigrants and 955 among Danish-born patients. Both male (RR=0.65; 95%CI: 0.46;0.90) and female (RR=0.64; 95%CI: 0.48;0.85) non-Western immigrants had a significantly lower risk ratio of hospital attendance for anaphylaxis compared to Danish-born. Compared to Danish-born, non-Western immigrants living in Denmark during the entire follow-up period also showed a decreased risk (RR=0.65; 95%CI: 0.34;1.25). Compared to Danish-born, non-Western immigrants who obtained residence permission as children had a decreased risk of hospital attendance for anaphylaxis (RR=0.48; 95%CI: 0.25;0.91).

CONCLUSION:
This Danish register-based study using nationwide data revealed fewer hospital attendances for anaphylaxis among non-Western immigrants compared to Danish-born; however this protection was lost over time.