BOISE, Idaho (AP) — Idaho health officials are trying to determine what is causing the gastrointestinal illness that has affected commercial and private rafters on the Middle Fork of the Salmon River, as well as fire personnel.

Mike Taylor, an epidemiologist with the Eastern Idaho Public Health District, tells the Idaho Statesman (http://bit.ly/1f4HI5f ) that river guides have fallen ill and a Forest Service weed control crew had to be flown out after getting sick. Taylor suspects it may be norovirus, a highly-contagious viral illness that causes nausea, vomiting and diarrhea and lasts for about two days.

About 50 people have reported getting ill while rafting or working on the river in the past month. However, three people who were tested came back with three different illnesses — one had norovirus, one had E. coli and one had giardia.