Thirty fi ve members of a tour group fl ew from Boston to Los Angeles. Of them, 5 developed symptoms of nausea and vomiting with a sixth experiencing multiple episodes of diarrhea. Patients walked throughout the airplane with one toilet needing to be closed due to soilage. Eventually, 15 members of the group and 8 non-tour group passengers were diagnosed with the same illness, with the culprit identifi ed in the stool of sick tour group members and one other passenger. What is the likely cause of this illness (Hannah et al. 2008)?