About 80 percent of the time the illness results from bacterial infection.
Prevention is the best defense.
With both bacteria and parasites, the main mechanisms of transfer are contaminated food or water. Raw vegetables and fruits, under-cooked eggs and fish, raw shellfish and unpasteurized milk and dairy products are common food sources. In wilderness areas, all untested water should be properly treated before drinking. Clean cold water in pristine settings may need only filtration against protozoan organisms. Otherwise all standing water should be disinfected by boiling for a minimum of five minutes plus one minute for each 1,000 feet of altitude above sea level, or by chemical treatment.