1. A 27-year-old woman presents to the emergency department complaining of 10-12 episodes of nonbloody diarrhea per day for the past 2 days, along with severe abdominal cramps, nausea, vomiting, and a low-grade fever. She states that she just returned from a vacation to Mexico. While in Mexico, she did not drink any of the local water and ate only cooked foods and a few fresh salads. If fecal leukocytes are present, the patient should most likely be empirically treated with