(CBS) — Federal health officials are investigating an E.coli outbreak that has sickened dozens of people.

Fast-food chain Wendy’s is pulling romaine lettuce from its sandwiches in some restaurants while the E.coli outbreak is investigated.

Nearly 40 people have now been infected with the outbreak strain E.coli 0157 in 4 states with most of the cases from Michigan and Ohio, according to the CDC.

At least 10 people have been hospitalized, including three in Michigan, with a type of kidney failure.

The CDC says people should call their healthcare provider if they have severe E.coli symptoms such as:

  • Diarrhea that lasts for more than 3 days
  • Diarrhea accompanied by a fever higher than 102
  • Bloody diarrhea
  • So much vomiting that you cannot keep liquids down

A specific food has not been confirmed as the source of the outbreak, but most people reported eating sandwiches with romaine lettuce at Wendy’s restaurants before getting sick. A different type of romaine lettuce is used in salads.

The CDC is also asking for the public’s help. If you have E.coli symptoms, write down what you ate in the week before you became ill and report the illness to your local or state health department.

There is no evidence at this time that the romaine lettuce sold in grocery stores is connected to this outbreak.