MINNEAPOLIS (AP) -- Hennepin County officials say they still don't know why more than 170 people got sick after boating near Big Island in Lake Minnetonka last weekend.

Officials have interviewed 225 people and have confirmed that 172 of them were near Big Island over the July Fourth holiday and became sick with vomiting, diarrhea or both.

Hennepin County Public Health epidemiology manager Dave Johnson says the illness does not seem to have spread since then. He says most people were sick for a few days and have recovered.


But the illness is a mystery. A test of one person's stool came back negative on all 22 viruses, bacteria, and parasites that typically lead to diarrhea and vomiting.

Johnson says people should not swim if they are sick and "don't use the lake as a toilet."