43) Afather and son come to your office because of persistent | Paediatrics videos & books

43) Afather and son come to your office because of persistent diarrhea. They relate the presence of watery diarrhea for over 2 weeks. They noted that the diarrhea began after returning from a Boy Scout camping trip in the Rocky Mountains. The diarrhea has waxed and waned for 2 weeks. It is nonbloody and foul smelling. They have had increased flatulence and mild abdominal cramping.
What is the most likely etiology of their diarrhea?