As cases of potentially deadly botulism in babies who drank ByHeart infant formula continue to grow, state officials say they are still finding the recalled product on some store shelves.

Investigators in at least three states found ByHeart formula for sale a week after the New York-based company recalled all products nationwide, officials told The Associated Press.

At least 31 babies in 15 states who drank ByHeart formula have been hospitalized and treated for infantile botulism since August, federal health officials said Wednesday. They range in age from about 2 weeks to about 6 months, with the most recent case reported on Nov. 13.

No deaths have been reported.

In Oregon, nine of more than 150 stores checked still had the formula on shelves this week, a state agriculture official said. In Minnesota, investigators conducted 119 checks between Nov. 13 and Nov. 17 and removed recalled products from sale at four sites, an agriculture department official said. An Arizona health official also said they found the product available.

Businesses and consumers should remain alert, Minnesota officials said in a statement. “No affected product should be sold or consumed,” they wrote.

Investigators with the U.S. Food and Drug Administration conducted inspections at ByHeart manufacturing plants in Allerton, Iowa, and Portland, Oregon. No results from the inspections have been reported.

ByHeart officials said they voluntarily recalled their products “in close cooperation” with the FDA, “despite the fact that no unopened ByHeart product has tested positive" for the spores or toxin that cause infant botulism.

California officials previously confirmed the type of bacteria that can lead to illness was confirmed in an open can of ByHeart formula fed to a baby who developed botulism.

Infant botulism, which can cause paralysis and death, is caused by a type of bacteria that forms spores that germinate in a baby's gut and produce a toxin.

Symptoms can take up to 30 days to develop and include constipation, poor feeding, a weak cry, drooping eyelids or a flat facial expression. Babies can develop weakness in their limbs and head and may feel “floppy.” They can have trouble swallowing or breathing.

ByHeart had been manufacturing about 200,000 cans of formula per month. It was sold online or at retail stores such as Target and Walmart. A Walmart spokesperson said the company swiftly issued a restriction that prevented sale of the formula, removed the product from stores and notified consumers who had bought it. Customers can visit any store for a refund of the formula, which sold for about $42 per can.

Federal and state health officials are concerned that some parents and caregivers may still have ByHeart products in their homes. They are advising consumers to stop using the product — including formula in cans and any singe-serve sticks. They also suggest marking it “DO NOT USE” and keeping it for at least a month in case a baby develops symptoms. In that case, the formula would need to be tested.

The California health department operates the Infant Botulism Treatment and Prevention Program, which tracks cases and distributes treatment for the disease. Officials there have launched a public hotline at 833-398-2022, which is staffed with health officials from 7 a.m. to 11 p.m. Pacific Standard Time.

The hotline has fielded hundreds of calls from parents and caregivers to date, officials said. It is being operated in addition to a longstanding hotline for doctors to discuss suspected infant botulism cases.

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The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education and the Robert Wood Johnson Foundation. The AP is solely responsible for all content.