Washtenaw County health department officials say they believe an E. coli outbreak that sickened at least 10 people has been contained.

But health officials say they have not yet confirmed the source of the contamination.

No additional similar illnesses have been reported in recent days, which would suggest the spread of the illness was contained to a time period of a couple of days, said county health department spokeswoman Susan Cerniglia.

Preliminary tests indicated 10 people were sickened, the health department announced Monday. The department is awaiting tests results to confirm whether additional people were also sickened by E. coli.

As they continue to investigate the source, officials are not telling county residents to avoid any particular foods at this point, Cerniglia said.

"If we thought people were still being exposed, different actions would be taken," she said.

The first cases of illness were reported on Thursday, said Laura Bauman, an epidemiologist for the county health department.

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.

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

E. coli can be spread from cattle to people by 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. Children may be contagious for up to three weeks.

Although officials do not believe E. coli is actively being spread, at this point, any one who does develop bloody diarrhea should seek medical attention. They should also report suspected E. coli illness to Washtenaw County Public Health at 734-544-6700.

Bauman said identifying the source can be a challenge because the incubation period for E. coli illness can be several days before a person shows symptoms. Those sickened must try to remember everything they consumed for the previous seven days from the first day they began showing symptoms.

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.