A 24-year-old male has recently returned from a weekend camping trip with friends. He has ulcerative colitis and a history of migraine headaches. He reports a 2-day history of headache, nausea, and vomiting with weakness. Which of the following is least likely as a possible cause?
a. Migraine headache
b. Exacerbation of ulcerative colitis
c. Acute gastroenteritis
d. Norovirus