Tests of ByHeart infant formula tied to a botulism outbreak that has sickened dozens of babies showed that all of the company's products may have been contaminated.

Laboratory tests of 36 samples of formula from three different lots showed that five samples contained the type of bacteria that can lead to the rare and potentially deadly illness, the company said Monday on its website.

“Based on these results, we cannot rule out the risk that all ByHeart formula across all product lots may have been contaminated,” the company wrote.

At least 31 babies in 15 states who consumed ByHeart formula have been sickened in the outbreak that began in August, according to federal and state health officials. In addition, other infants who drank ByHeart formula were treated for botulism in earlier months, as far back as November 2024, although they are not counted in the outbreak, officials said.

Clostridium botulinum type A, the type of bacteria detected, can be unevenly distributed in powdered formula. Not all babies who ingest it will become ill, though all infants under age 1 are at risk, medical experts said.

ByHeart recalled all of its formula nationwide on Nov. 11. However, some product has remained on store shelves despite the recall, according to state officials and the U.S. Food and Drug Administration.

Parents and caregivers should stop feeding the formula to babies immediately and monitor the children for symptoms, which can take up to 30 days to appear.

Infant botulism occurs when babies ingest spores that germinate in their intestine and produce a toxin. Symptoms include constipation, difficulty sucking or feeding, drooping eyelids, flat facial expression and weakness in the arms, legs and head. The illness is a medical emergency and requires immediate treatment.

At least 107 babies nationwide have been treated for botulism with an IV medication known as BabyBIG since Aug. 1, health officials said. In a typical year, less than 200 infants are treated for the illness.

To report an illness tied to the outbreak, contact an FDA consumer complaint coordinator or fill out an online MedWatch form.

Consumers who bought ByHeart on the company's website on or after Aug. 1 can receive a full refund, an expansion of its previous policy, the company said.

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