Alternative definition : FDA: Progression of anaphylaxis into systemic shock, which is characterized by significant
reduction in tissue perfusion which leads to hypoxia and hypotension, and can lead
to death if untreated.; NCI-GLOSS: A severe and sometimes life-threatening immune system reaction to an antigen
that a person has been previously exposed to. The reaction may include itchy skin,
edema, collapsed blood vessels, fainting, difficulty in breathing, and death.;