LINCOLN, NE (AP) — A hepatitis A outbreak in Nebraska, Indiana and Wisconsin has been traced to blackberries sold in Fresh Thyme grocery stores and federal authorities on Wednesday warned consumers in 11 states against eating some berries bought from that chain.

The Nebraska Department of Health and Human Services said in a news release that the outbreak began several weeks ago in Nebraska. The department said it, the U.S. Food and Drug Administration and the Centers for Disease Control and Prevention are investigating and have confirmed 11 cases of the virus, including six in Nebraska.

Fresh Thyme said in a written statement that it’s cooperating with the investigation, working to identify its suppliers and isolate the source of the contamination.

“At this time, there is no reason to believe that any of the product was contaminated via handling in our stores,” the company said.

The FDA urged consumers in Nebraska, Indiana, Wisconsin, Iowa, Illinois, Kentucky, Michigan, Missouri, Minnesota, Ohio and Pennsylvania to not to eat any fresh blackberries bought from Fresh Thyme between Sept. 9 and Sept. 30.

Anyone who froze the berries for later use should throw them out, the FDA said.

Hepatitis A is a virus that infects the liver and can cause mild, flu-like symptoms for several weeks.