North-south differences in US emergency department visits for acute allergic reactions

In a previous study, latitude was positively associated with EpiPen prescription rates.

To determine whether a similar geographic difference exists for emergency department (ED) visits for acute allergic reactions (including anaphylaxis).

We combined National Hospital Ambulatory Medical Care Survey data for ED visits to noninstitutional hospitals from 1993 to 2005. Acute allergic reactions were identified by International Classification of Diseases, Ninth Revision, Clinical Modification codes 995.0, 995.60-995.69, 995.1, 995.2, 995.3, 989.5, and 693.1, and visit rates were compared across standardized geographic divisions.

Between 1993 and 2005, there were 17.3 million ED visits for acute allergic reactions, representing 1.3% (95% confidence interval [CI], 1.2%-1.3%) of all ED visits. Per 1000 population, the Northeast had 5.5 visits (95% CI, 4.7-6.2 visits) and the South had 4.9 visits (95% CI, 4.3-5.6 visits). In a multivariable model, the Northeast had a higher odds ratio (OR) than the South (1.13; 95% CI, 1.01-1.27; P = .04). The association was stronger when restricting the analysis to visits for food-related allergic reactions (OR, 1.33; 95% CI, 1.14-1.56; P < .001).

The ED visit rates for acute allergic reactions are higher in northeastern vs southern regions. These observational data are consistent with the hypothesis that vitamin D may play an etiologic role in anaphylaxis, especially food-induced anaphylaxis.