Review Question - QID 214593

A 45-year-old man presents to the emergency department after several episodes of nausea and vomiting. The patient states that he feels nauseous currently. He was at a company picnic the day before where he consumed potato salad and barbecued meats. He has a history of diabetes and hypertension. The patient is currently sexually active with multiple partners and intermittently uses condoms. He recently was exposed to cesium-containing waste at his work but did not report this to his employer as he felt fine afterwards. His temperature is 97.6°F (36.4°C), blood pressure is 110/70 mmHg, pulse is 110/min, respirations are 19/min, and oxygen saturation is 98% on room air. Physical exam reveals a healthy appearing man with normal breath sounds and heart sounds. He is observed in the emergency department and suddenly has several episodes of vomiting and bloody diarrhea. He is admitted to the hospital. On day 2 in the hospital, laboratory studies are ordered as seen below.

Hemoglobin: 12 g/dL
Hematocrit: 36%
Leukocyte count: 1,500/mm^3 with 1.0% lymphocytes
Platelet count: 109,500/mm^3

The patient's gastrointestinal symptoms have worsened during this time frame. Which of the following is the most likely etiology of this patient's symptoms?