LOS ANGELES, Dec. 10 (Xinhua) -- A total of 51 infant botulism cases have been reported across 19 U.S. states as of Wednesday amid a nationwide recall of potentially contaminated infant formula, according to an update from the U.S. Food and Drug Administration (FDA).

Epidemiologic and laboratory evidence indicated that ByHeart Whole Nutrition infant formula may be contaminated with Clostridium botulinum, which is causing infant illness in multiple regions of the country, the FDA said.

Investigations by both ByHeart and the FDA into the root cause of the contamination are ongoing. At this stage, the FDA said it cannot rule out the possibility that all ByHeart infant formula products may have been affected.

In response, the U.S. Centers for Disease Control and Prevention (CDC) broadened its case definition to include any infant with botulism who was exposed to ByHeart formula at any time since the product's launch in March 2022.

Previously, case counts only included illnesses beginning on or after Aug. 1, 2025. With the expanded definition, the CDC and state health partners identified 10 additional cases that occurred between December 2023 and July 2025.

Illness onset dates range from Dec. 24, 2023 to Dec. 1, 2025. All 51 affected infants were hospitalized, but no deaths have been reported to date. The infants range in age from 16 days to 264 days, and 43 percent are female, according to the FDA.

State and local public health officials are interviewing caregivers about foods the infants consumed in the month prior to becoming sick. All 51 infants had been fed ByHeart Whole Nutrition powdered formula before falling ill.

Additional testing by ByHeart, the FDA, the CDC, and state partners is underway, with results expected in the coming weeks.

The FDA said its investigation continues to determine the point at which contamination occurred. ■