Washtenaw County officials are warning county residents about a suspected outbreak of E. coli cases among local residents.

Ten cases have been reported to public health officials and other cases are being investigated, according to a release. Preliminary tests have come back positive for a toxin that is usually detected with E. coli illness, said Laura Bauman, an epidemiologist for the county health department.

Microscopic image of E. coli bacteria.

Symptoms most often include abdominal cramping followed by progressively worsening diarrhea that is bloody. Those who have been sickened have mostly been young adults and at least a couple of those cases have ended up in the hospital. Most of them live in Ann Arbor.

E. coli can be spread from cattle to people through eating raw or undercooked beef (especially ground beef). It can also be spread by consuming contaminated water or foods such as melons, lettuce, spinach, apple cider, alfalfa sprouts, or unpasteurized milk, according to a fact sheet from the county.

Infected individuals may spread the illness to others by not washing their hands well after a bowel movement. An adult infected with E. coli is contagious for a week. However, children may be contagious for up to three weeks.

County health officials advise residents to store thawing and uneaten cooked foods in the refrigerator, to keep cooked meat and other foods from coming in contact with surfaces that raw meat has touched and to disinfect cutting boards and counters and wash hands properly after going to the bathroom or changing a diaper.

Anyone who develops bloody diarrhea should seek medical attention and should report suspected E. coli illness to Washtenaw County Public Health at 734-544-6700.

"We're still wanting to make sure we don't have any more cases out there and, as we talk to everyone, we're tyring to find the common denominator," Bauman said.

Identifying the source can be a challenge, Bauman said, because to do that, officials ask those who have been sickened about everything they've eaten in the seven days previous to the first day they became ill.

“We are in the early stages of our investigation, and we are doing everything we can to identify probable cases and to prevent any additional illness," Diana Torres-Burgos, medical director for Washtenaw County Public Health, said in a release. The county is still working to identify the strain of E. coli and how many people might be affected, she said.

In Washtenaw County, about six cases of E. coli sickness are normally reported to the county public health department annually, the department said. Most recover within a week, but some infections can be more serious.

Update: Washtenaw County E. coli outbreak not believed to be spreading

Tina Reed covers health and the environment for AnnArbor.com. You can reach her at tinareed@annarbor.com, call her at 734-623-2535 or find her on Twitter @TreedinAA.