The U.S. Food and Drug Administration has sent warning letters to major retailers including Albertsons, Kroger, Target and Walmart for "failing to remove" recalled ByHeart infant formula products from store shelves that have been linked to at least 51 infant botulism cases so far.
The federal agency announced the move in a Monday release, calling for companies to adopt "best practices in recall implementation, especially for recalls involving foods for ... infants and young children."
All of ByHeart's Whole Nutrition Infant Formula products, including all cans and Anywhere Pack single-serve sticks, were voluntarily recalled online and in stores on Nov. 11.
ByHeart's formula products are linked to an outbreak of infant botulism, a type of severe illness caused by botulinum toxin, according to the Centers for Disease Control and Prevention and the FDA.
So far, at least 51 children between the ages of 2 weeks and 9 months have been hospitalized across 19 states, the agencies stated in recent outbreak investigation updates.
The FDA said investigators checked store shelves over 4,000 times across the country in the wake of the recall to ensure consumers wouldn't be able to buy any of the affected products but found recalled formula in over 175 store locations across 36 states. In one instance, the FDA said, the recalled formula continued to be available to consumers "for over three weeks."
"When a food is recalled, every industry member along the supply chain plays an important role in carrying out the recall," the agency said in its release. "Retailers play the especially crucial role in the last step of the supply chain by ensuring that recalled products are immediately removed and not available to consumers at their stores."
"The agency is particularly concerned with these retailers' capability to quickly remove unsafe products from their store shelves and ensure it remains off shelves as required during a public health emergency," it added.
Retailers have 15 days to respond to the FDA to explain what the companies have done to address any potential violations and prevent any future violations.
In a statement to ABC News, Walmart said, "The health and safety of our customers and members is always a top priority. When notified of the recall, we moved swiftly to issue a sales restriction and removed this product from our impacted stores and clubs and online. We take all reports of inaction seriously and will respond to the letter."
Albertsons Companies said in a separate statement to ABC News this week, "At Albertsons Companies, we are committed to the health and safety of our customers. We have procedures to address product recalls, including working closely with suppliers and regulators to identify and remove affected items and communicate guidance to customers. ByHeart infant formula products have been removed from our store shelves."
ByHeart president and co-founder Mia Funt told ABC News previously that "the safety and well‑being of every infant who uses our formula is, and always will be, our highest priority."
In a Nov. 24 statement on its website, ByHeart said that as soon as it learned about the outbreak, "we immediately partnered with IEH Laboratories & Consulting Group ... to test un-opened cans of ByHeart product, and conducted a nationwide recall."
"We tested 36 samples from three lots and ... received positive test results for Clostridium botulinum Type A in five of the 36 samples across all three lots. Based on these results, we cannot rule out the risk that all ByHeart formula across all product lots may have been contaminated," the company said at the time.
It added, "We continue to be focused on finding the root cause, through a rigorous audit of every step of our product development chain, from suppliers and raw ingredients, through to packaging and transportation. This includes testing more product samples."
The multistate outbreak of infant botulism remains under investigation by the FDA, CDC, the California Department of Public Health Infant Botulism Treatment and Prevention Program, and other state and local health authorities.
ByHeart is offering anyone with recalled ByHeart formula purchased on the company's website on or after Aug. 1 a full refund. Affected customers can reach out to ByHeart at 866-201-9069. Customers who bought recalled formula at another retailer can reach out to the individual retailer for more information about refund policies.
Botulism is a rare but serious illness. According to the CDC, botulinum toxin can attack the nerves, leading to difficulty breathing, muscle weakness and paralysis, visual disturbances, trouble swallowing, speech issues and, in some instances, death.
Infant botulism occurs when a baby swallows Clostridium botulinum spores, which can then grow in the gut and produce the botulinum toxin, the agency states.
Symptoms of infant botulism can include poor feeding, constipation, pupils that are slow to react to light, drooping eyelids, fewer facial expressions than usual, low muscle tone or a weaker-than-normal cry.
"Seek immediate medical care if your infant has consumed ByHeart Whole Nutrition Infant Formula and has any of these symptoms: poor feeding; loss of head control; difficulty swallowing; decreased facial expression," the CDC stated in its most recent outbreak update.
