A case of late-onset anaphylaxis caused by natto

Abstract

A 29-year-old man presented with wheals, nausea, and vomiting, and he was diagnosed with anaphylaxis by a nearby clinic. Thereafter, he suffered from five anaphylactic episodes with symptoms including abdominal cramps, wheals, nausea, vomiting, and decreased blood pressure. Since he had ingested "natto (fermented soybeans)" the day before each of the fourth and fifth anaphylactic episodes, late-onset anaphylaxis against natto was suspected. A skin prick-to-prick test for natto was positive, and after an oral challenge with natto, he developed pharyngeal discomfort and wheals accompanied by a severe decrease in blood pressure six hours after ingestion. Therefore, this case was diagnosed as anaphylaxis due to natto. No anaphylactic or allergic symptoms have occurred after he stopped eating natto.