Health officials are investigating an outbreak of intestinal illness cases reported in the Tri-Cities during the weekend.

The cause of the outbreak has not been determined though Susan Shelton with the Benton Franklin Health District said there were at least 20 documented cases as of Tuesday evening.

Anyone who has symptoms, including nausea, vomiting and diarrhea, should contact their health care provider for treatment.

Health care professionals then are encouraged to report the cases to health department officials.

"We are very early in our investigation," she said.

Exact figures weren't immediately available but three people were treated for gastroenteritis at Kennewick General Hospital, a hospital official confirmed.

All three said they had attended the RadCon science fiction and fantasy convention in Pasco over the weekend before feeling ill.

Several others were treated for nausea, vomiting and diarrhea at Kadlec Regional Medical Center in Richland, said spokesman Jim Hall.

And Lourdes Medical Center in Pasco did not immediately report whether it treated similar cases in recent days.

A public service notice about the outbreak was posted on pages and profiles throughout the social networking website Facebook, encouraging people who were ill to contact the health district.

Shelton said she and health officials still are piecing together information as they look for a cause.

"We're looking for commonalties," she said.

-- Ty Beaver: 582-1402; tbeaver@tricityherald.com