Management of gastroenteritis focuses on supportive care, such as maintaining adequate hydration with an oral rehydration solution. Antimicrobials should be avoided as they can increase the likelihood of developing hemolytic uremic syndrome (HUS) in patients infected with EHEC. Beta-lactam antibiotics such as ceftriaxone (Choice A) are among the medications most commonly associated with HUS. Ceftriaxone is appropriate only in patients who appear septic or bacteremic. However, this patient's normal vital signs and nontoxic appearance argue against sepsis.