A child who lives on Mercer Island likely has E. coli, public health officials said Sunday.

The state laboratory has yet to confirm the case, and King County public health officials say it's not possible to say whether there is a link between the child's illness and problems with the Mercer Island water system.

The child, who is not hospitalized, had multiple possible exposures to E. coli, including water from the Mercer Island system and foods that can be contaminated with the bacteria, health officials said.

King County has about 20 to 30 cases of E. coli each year. The source of most cases is never identified, health officials say.

"E. coli comes from a variety of sources including ground beef, unpasteurized milk and cheese, and produce. We may never be able to definitively link this case to a particular source," Dr. Meagan Kay, medical epidemiologist for Public Health - Seattle & King County, said in a statement.

Officials started advising residents of the Seattle suburb to boil their water after some city water tested positive for E. coli. Tests

Health officials reported on Sunday that samples collected Friday and Saturday all tested negative for E. coli, but they have decided to continue to advise people to boil their water. Saturday included seven samples from residential properties.

Mercer Island schools will be in session Monday on their regular schedule.

Twice this week, residents of this island in the middle of Lake Washington were told to take precautions with their tap water. That forced about 60 businesses to close. About 15 restaurants were allowed to open this weekend, but they must follow special procedures.

The source of two different positive E. coli test results has yet to be identified, Mercer Island police Cmdr. Leslie Burns said