Jan 23 (Reuters) - U.S. Health officials found spores that can cause infant botulism at a supplier for formula-maker ByHeart during an investigation into an outbreak that has sickened dozens of babies, Bloomberg News reported on Friday, citing a document.

Infant botulism occurs when babies ingest spores of the bacteria Clostridium botulinum, which can grow in their immature digestive systems and produce the toxin.

Symptoms include constipation, poor feeding, loss of head control and difficulty in swallowing. In severe cases, infants can develop breathing problems.

U.S. Food and Drug Administration inspectors had found sanitation issues at some of ByHeart's factories over the last few years, and it had been unclear whether it was those conditions or an ingredient from an outside supplier that was the source of the contamination, the Bloomberg report said.

The document did not identify the contaminated ingredient or its maker, the report added.

As of December 17, 2025, an outbreak of the illness had sickened 51 infants across 19 states, according to the Centers for Disease Control and Prevention.

ByHeart claimed to have made the "closest to breast milk" formula with organic ingredients, the report added.

ByHeart initially recalled certain lots of its formula, in November. Three days later, it expanded the recall to include all its infant formula products.

The recall covered both cans and single-serve stick packs.

The FDA sent warning letters to four major retailers including Walmart WMT.O, Target TGT.N, Kroger KR.N and Albertsons ACI.N last month for continuing to sell baby formula linked to infant botulism, even after the products were recalled.

(Reporting by Siddhi Mahatole in Bengaluru; Editing by Alan Barona)

((siddhi.mahatole@thomsonreuters.com;))