The Food and Drug Administration is now warning hospitals not to give probiotics to preterm infants, after a baby was killed by bacteria linked to a probiotic.

An investigation has also now been launched into the death, the FDA announced in a warning published Friday, which followed use of Evivo with MCT Oil, a probiotic manufactured by California-based Infinant Health that is now being recalled.

"Genomic sequencing data demonstrate the bacterium that caused sepsis in this infant was a genetic match to the bacteria contained in this probiotic," the agency said.

It is not clear which hospital administered the probiotic now being investigated by the FDA. An agency spokesperson did not immediately respond to a request for comment.

In a statement, a spokesperson for Infinant Health said the company is "cooperating with FDA's ongoing investigation." The company has voluntarily agreed with FDA to stop shipping its Evivo with MCT Oil product, the spokesperson said.

"That product was used by health care professionals in hospital settings, including neonatal care for preterm infants," the company said in its statement.

In a separate warning letter Friday, the FDA also alleged Infinant Health had overstepped its boundaries as a dietary supplement manufacturer. Medical claims about the product were on par with an "unapproved new drug and unlicensed biological product" that would be illegal to sell in the U.S.

The company is planning to continue distributing its "Evivo powder product" for consumers to buy, Infinant Health's spokesperson said. They also intend "to work with the FDA toward approval of the use of our MCT oil product in hospital settings."

In a May news release, Infinant Health had claimed its Evivo probiotics are "widely used by parents" as well as in hospitals and neonatal intensive care units "throughout the U.S." 

Probiotics are bacteria eaten for health benefits, such as those in yogurt or supplements. Studies have shown some benefits for infants taking probiotics in guarding against some diseases.

Infinant Health makes a number of claims about its Evivo product for consumers, including that babies fed the probiotic have better sleep, less diaper rash and "a healthy gut microbiome."

"For parents asking, 'Should I give my baby probiotics?' note that 80% of our immune system is in our gut. It's imperative to care for your baby's gut microbiome today to give them a strong foundation for good health," the company says.

On its website, the company says in an FAQ for doctors that the product can be started "right after birth" alongside breast milk.

The FDA warns that no probiotics have been approved for use as a drug or biological product in babies, meaning probiotics are not subject to the "agency's rigorous manufacturing and testing standards" for other medications regulated by the FDA.

Instead, probiotics are allowed to be sold in the U.S. as dietary supplements, bypassing the FDA's higher bar for drug and biologics approvals.

"Evivo is a food for special dietary use, meeting all FDA regulations for food products, and has been used by parents, hospitals and providers for five years with over 4.7 million feedings to date in over 60,000 babies," the company said in its May news release.

The FDA also pointed to recommendations from the American Academy of Pediatrics counseling against wide use of probiotics for preterm infants. 

That 2021 report cited data suggesting 1 in 10 "extremely low gestational age" babies were now being given probiotics by hospitals.

"Given the lack of FDA-regulated pharmaceutical-grade products in the United States, conflicting data on safety and efficacy, and potential for harm in a highly vulnerable population, current evidence does not support the routine, universal administration of probiotics to preterm infants," the report's authors wrote.

Alexander Tin

CBS News reporter covering public health and the pandemic.