Final answer:
The 19-year-old male with a severe allergy to seafood is at the greatest risk for anaphylactic shock, which is a rapid and potentially fatal hypersensitivity reaction treatable with epinephrine.
Step-by-step explanation:
The client at the greatest risk of developing anaphylactic shock is the 19-year-old male with a severe allergy to seafood. Anaphylactic shock is a systemic and potentially life-threatening type I hypersensitivity reaction. When an individual with a severe allergy to a specific allergen, such as seafood, is exposed to that allergen, systemic mast cell degranulation occurs, leading to a drop in blood pressure, contractions of bronchial smooth muscle, and other life-threatening symptoms. These reactions can be fatal within 20 to 30 minutes if left untreated. The primary drug used to counteract the effects of anaphylaxis is epinephrine, which raises blood pressure and relaxes bronchial smooth muscles. Individuals with known severe allergies are often prescribed epinephrine autoinjectors to carry with them at all times.