Which of the following is considered a systemic symptom of anaphylaxis?

Anaphylaxis is a severe and potentially life-threatening allergic reaction that involves multiple body systems. It typically presents with a rapid onset of symptoms affecting the skin, respiratory tract, gastrointestinal tract, and cardiovascular system. The gastrointestinal symptoms such as diarrhea and vomiting are considered systemic because they indicate involvement of the overall body response to an allergen.

In anaphylaxis, the release of mediators like histamine from immune cells can cause vasodilation and increased permeability, affecting the gastrointestinal tract and leading to manifestations such as nausea, vomiting, and diarrhea. These symptoms reflect a systemic reaction rather than localized effects, highlighting the body's extreme response to an allergenic trigger, which can impact the entire organism.

While fever, headache, and myalgia may be associated with various medical conditions, they are not typically direct symptoms of anaphylaxis and do not reflect the immediate and severe systemic effects that characterize this allergic response. Diarrhea and vomiting thus stand out as key systemic symptoms specifically tied to the physiological responses during anaphylaxis.