The U.S. Food and Drug Administration, the U.S. Centers for Disease Control and Prevention and local authorities are investigating an outbreak of Listeria monocytogenes infections reported in eight states, the FDA said on Tuesday.

“To date, a positive sample of Fresh Express Sweet Hearts salad mix has been reported to match the outbreak strain,” Frank Yiannas, the FDA deputy commissioner for food policy and response, said in the statement.

“Our investigation is ongoing, and we will continue to communicate should additional products be implicated,” he added.

Listeria monocytogenes can cause “serious and sometimes fatal” infections in young children, frail or elderly people, as well as any others with weakened immune systems, the company said in an announcement published on Tuesday on the FDA website.

“Although healthy individuals may suffer only short-term symptoms such as high fever, severe headache, stiffness, nausea, abdominal pain and diarrhea, Listeria infection can cause miscarriages and stillbirths among pregnant women,” the company warned.

Fresh Express has since voluntarily recalled a selection of its salad products and customers are advised not to eat, sell or serve any recalled products.

The recall includes various fresh salad items with the product codes Z324 through Z350. Product codes can be seen on the front of the packages below the “use by” date. “No other Fresh Express products are subject to recall,” the company said.

Those who have already purchased the recalled products can get a refund by calling the Fresh Express Consumer Response Center at 1-800-242-5472 between 8 a.m. and 7 p.m. ET. Refunds are also available where the recalled items were purchased.

The recalled salad items were distributed through retailers in the country’s northeast and Midwest regions, as well as via distributors and retailers in Canada.

The U.S. states where the recalled products were distributed include Connecticut, Iowa, Illinois, Indiana, Kentucky, Massachusetts, Maryland, Maine, Michigan, Minnesota, Missouri, North Dakota, New Hampshire, New Jersey, New York, Ohio, Pennsylvania, Rhode Island and Wisconsin.

In Canada, they were distributed in the provinces of Ontario and Manitoba.

Salad Products in the Fresh Express Recall

Listed in the table below (in alphabetical order) are the salad products recalled by Fresh Express, as outlined at the FDA website.