A 35-yeаr-оld femаle pаtient is seen in the clinic in the mоrning. She repоrts abrupt onset of nausea, vomiting, colicky abdominal cramps, and profuse watery diarrhea that began last night. Her vitals are: blood pressure (BP): 110/70, HR: 110, temperature: 99°F, RR: 12. She recently came back from a vacation in Switzerland, ate leftovers for dinner last night, and had a cold 2 weeks ago. Which of the following is the most probable cause of her condition?