Systemic urticaria in an infant after ingestion of processed food that contained a trace quantity of wheat.

BACKGROUND: Wheat is a food allergen that occasionally causes a systemic allergic reaction; however, little is known about the quantities of wheat allergen required to evoke allergic symptoms. OBJECTIVE: To report the case of a wheat allergic boy who experienced systemic urticaria and angioedema within 40 minutes after the ingestion of 9 g of packed rice crackers. METHODS: A skin prick test and IgE immunoblotting with wheat proteins were performed. Contamination of wheat protein in the offending rice cracker and other processed rice crackers from local food retail outlets, with labels that did not mention wheat, was examined with enzyme-linked immunosorbent assaying. RESULTS: A skin reaction to wheat was positive. IgE-bound bands were observed with water- and salt-soluble wheat protein and ethanol-soluble wheat gliadin in immunoblotting. A trace quantity of wheat protein, 1.50 microg/g, was determined in the offending rice cracker. In addition, 3 of 8 other kinds of processed rice crackers were contaminated by wheat protein, with levels ranging from 0.26 to 1.13 microg/g. CONCLUSIONS: Approximately 13.5 microg of wheat protein can elicit a systemic adverse reaction in highly sensitive, wheat allergic individuals. The present study confirms the need for control of contamination of food by nondeclared proteins.