ELISA is a biochemical technique used in immunology to detect antibodies or antigens in a sample. It works by attaching an unknown antigen to a surface, applying the antibody, and using an enzyme to detect the antigen-antibody complex. ELISA is useful for medical tests like HIV and West Nile Virus tests. Hives are itchy red welts on the skin caused by allergic reactions. Symptoms include swelling and itching and treatment involves antihistamines. Nosocomial infections are those acquired during medical treatment in places like hospitals, where infections are sometimes transmitted due to lack of hygiene among hospital workers.