INDIANAPOLIS — Health professionals are trying to figure out what is behind an outbreak of E. coli that has sickened people in two states.

On Wednesday, the CDC announced that it is working with public health and regulatory officials in Michigan and Ohio to identify what is behind the outbreak. They are using different types of data to identify the food source.

The investigation comes after Michigan and Ohio reported large increases in the number of E. coli infections in their states. The CDC says most people infected with Shiga toxin-producing E. coli experience severe stomach cramps, diarrhea, and vomiting three to four days after swallowing the bacteria.

While most people recover without treatment within 5 to 7 days, some people may develop a type of kidney failure and need to be hospitalized.

As of Tuesday, 29 people have been confirmed to be infected with the outbreak strain. The illnesses started on dates ranging July 26 to August 6.

Those sickened by the outbreak strain include people aged 6 to 91. Most of the people that were sickened were male. While nine people have been hospitalized with the outbreak strain so far, no deaths have been reported.

The CDC said the true number of such people in the outbreak is likely higher than the reported number, and the outbreak may not be limited to Michigan and Ohio. This is because some of the recent illnesses have not been reported to PulseNet, as it usually takes three to four weeks to determine if a person is part of an outbreak. Other people may recover without medical care so they are not tested.

If a food item is identified as the cause of the outbreak, the CDC said investigators will issue advice for people and businesses. They encourage people with E. coli symptoms to report it to their local or state government.

To prevent getting sick with E. coli, the CDC encourages people to follow the following four food safety tips:

• Clean: Wash your hands, utensils, and surfaces often. Rinse fruits and vegetables under running water before eating, cutting, or peeling.
• Separate: Keep food that won’t be cooked separate from raw meat, poultry, and seafood.
• Cook: Use a food thermometer to make sure you have cooked your food to a temperature high enough to kill germs.
• Chill: Refrigerate perishable food (food that goes bad) within 2 hours. If the food is exposed to temperatures above 90°F (like a hot car or picnic), refrigerate within 1 hour. Thaw food in the refrigerator, not on the counter.