Four of the nation’s top retailers failed to promptly pull contaminated infant formula linked to a dangerous botulism outbreak from their shelves, federal health officials said in warning letters posted Monday. The U.S. Food and Drug Administration sent letters to leaders at Walmart, Target, Kroger and Albertsons, saying the companies continued to sell ByHeart infant formula for days or weeks, despite a Nov. 11 recall of all products in the outbreak that sickened more than 50 babies in 19 states. “As a participant in the supply chain, your firm must take prompt and effective action when notified of a product recall,” FDA officials said in warning letters sent to the companies on Dec. 12 and posted online Monday. The formula was found at Target stores in 20 states “well after the recall began,” one letter said. In addition, it was sold at a Target store in New Hampshire on Nov. 16 despite an electronic box on the product’s sales code, the FDA noted. And at a Target store in Arkansas, single-serve packets of ByHeart formula were promoted with a “Sold Out!” sign and a $2 discount from November 16th to November 22nd. Information from state and local health officials said ByHeart formula was found at Walmart stores in 21 states from Nov. 12 to Nov. 26. The formula was found in Albertsons stores in 11 states from November 12 to November 19, and at Kroger state stores from November 1 to November 10. companies failed to provide FDA with evidence that corrective actions had been taken, despite multiple requests, the agency said. The companies have 15 working days to respond to the letters. Walmart officials said in a statement that no ByHeart formula was sold after cash registers were blocked from selling the formula following the recall. “We moved quickly to issue a sales restriction and removed this product from our affected stores and clubs and online,” a company spokesperson said in an email. “We take all reports of inaction seriously and will respond to the letter.” Albertsons officials said the company worked closely with suppliers and regulators to identify and remove the products and communicate with customers. “ByHeart infant formula products have been removed from our store shelves,” the company said in a statement. All the babies in the outbreak were hospitalized and treated with an IV medication to stop the progression of the disease. The US Centers for Disease Control and Prevention has expanded the outbreak to include all babies treated for botulism after eating ByHeart formula since it was first manufactured in 2023. Steven Mandernach, executive director at the Association of Food and Drug Officials, said the FDA itself has been slow to share information about the recall with state and local food safety officials. The agency did not fully share product lists until Nov. 14 — nearly a week after the initial Nov. 8 recall of two lots of ByHeart formula. He said it was “disappointing” in an outbreak involving the only source of nutrition for vulnerable babies. “There probably wasn’t the sense of urgency to get the product off the market that I would expect,” Mandernach said. ___ 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.