Three sick from E. coli after swimming in Lake Minnetonka

Three cases of E. coli O157:H7 illness in Minnesotans have been linked to swimming in the Big Island area of Lake Minnetonka, state health officials reported.

The illnesses occurred in young adults, and all are residents of the seven-county metropolitan area. One of the cases was hospitalized but has since recovered. All of the cases reported swimming and boating on July 4 in the Big Island area of Lake Minnetonka, where boaters are known to gather.

Officials aren't yet certain of the source of the E. coli, but lakes can be contaminated by feces, individual septic systems or sewage spills, improper boat waste disposal or ill swimmers. People who swim when they are ill can easily contaminate the water - even if they don't have a fecal accident.

All public beaches on Lake Minnetonka remain open and have passed their regular water quality monitoring tests.

From 2000 to 2011, 24 swimming pool outbreaks and 15 beach outbreaks were identified in Minnesota, sickening 900 people. The most common symptom is diarrhea, which frequently is severe enough for hospitalization. Symptoms may not begin until a week or more after swimming. The parasite Cryptosporidium commonly causes waterborne disease; E. coli does very infrequently.

About 160 to 220 cases of E. coli O157:H7 are reported in Minnesota each year.

Anyone who thinks they may have E. coli should contact a health care provider.