Spokeswoman Suzanne Pate said the district's nurses noted two cases last week and on Friday asked Snohomish County physicians to do further testing if any patients came in with bloody diarrhea for at least two days — a symptom of E. coli.
By noon Monday, medical professionals in the county had reported a total 14 cases, none of which have yet been confirmed by additional testing, which can take several days.
Snohomish County has between 16 and 20 reported cases of E. coli in a year, "so this is a significant number," Pate said.
The source of the contamination isn't known, she said.
Health-district officials are reading through the nine-page questionnaire that the ill patients completed to check for anything in common, such as a place they visited.
Pate said E. coli is a fecal-oral form of contamination.
It could be picked up if someone "patted a sheep and ate cotton candy," for example, or changed a diaper, then prepared food without washing hands first, she said.
Seattle attorney Bill Marler said the biggest reservoir for E. coli is cattle feces. Marler represented some of the 600 people sickened during a 1993 E. coli outbreak linked to improperly cooked hamburgers at Jack in the Box restaurants.
"Whether it's contaminated lettuce or hamburger, you always have to look for the cow," Marler said.
The summer petting-zoo season is over, he said.
There's been a nationwide outbreak of E. coli contamination in the past 30 days.
On Monday, the U.S. Department of Agriculture said cattle fed an ethanol byproduct called distiller's grain, a cheap and common feed, have a higher concentration of acid in their digestive tracts and are more likely to have E. coli than cornfed cattle.
The Department of Agriculture didn't tell farmers to refrain from feeding distiller's grain to cattle.
Since early September, E. coli outbreaks have been linked to lettuce grown in California and beef sold in Vermont.
In addition to diarrhea, nausea and abdominal cramping, E. coli can cause kidney failure and in some cases be fatal.
Three children died in the 1993 outbreak at Jack in the Box restaurants.
"Public Health in Snohomish County is working to solve this disease puzzle," said director Dr. Gary Goldbaum.
"No single source is jumping out at us from the preliminary investigation. However, we learn more with each interview and each lab test."