Most of the infants sickened in last year’s nationwide outbreak of infant botulism linked to ByHeart baby formula required continued medical care after leaving the hospital, according to newly presented disease severity data that offer the clearest picture yet of how seriously the outbreak affected its youngest victims. The findings were presented Friday at the Centers for Disease Control and Prevention’s annual Epidemic Intelligence Service (EIS) Conference in Atlanta.
Myra Brooks, a first-year EIS officer with the CDC’s National Botulism Consultation Service who was involved in the outbreak response, presented the data. The CDC declared the ByHeart outbreak over on February 26, 2026, with 48 confirmed and probable cases across 17 states. All 48 affected infants required hospitalization; no deaths were reported. The outbreak is the first documented instance of infant botulism linked to powdered infant formula.
Most Cases Required Intensive Support, Extended Recovery
Investigators were able to review medical records for 46 of the 48 affected infants. The data revealed a distribution of illness severity that underscores the serious nature of the disease. Sixty-one percent of infants were classified as having moderate disease, requiring assisted feeding or non-invasive respiratory support during hospitalization. Eleven percent had severe disease and required intubation or a surgically placed feeding tube. The remaining 28 percent were classified as mild cases — though all still required hospitalization.
The median hospital stay was eight days, but some infants with severe disease remained hospitalized for more than a month. Brooks reported that one-third of infants were sent home with nasogastric tubes to supplement feeding, and two-thirds had follow-up orders for physical, speech, or occupational therapy. “Although many infants are now progressing in their recovery, evaluating their outcomes is essential to understanding the progression and severity of illness observed during this outbreak,” Brooks said.
Outbreak Timeline Stretched Back Further Than Initially Recognized
Infant botulism occurs when babies ingest spores of Clostridium botulinum bacteria, which then activate in the intestinal tract and produce a toxin capable of causing muscle weakness and paralysis. Initial symptoms typically include constipation, poor feeding, loss of head control, and difficulty swallowing. Without treatment, breathing difficulties can develop. The California Department of Public Health (CDPH) runs the national infant botulism program and distributes the only FDA-approved treatment for the condition. It was CDPH that first identified the outbreak in early November 2025, after noticing a spike in medication requests among infants who had consumed ByHeart formula.
The outbreak’s timeline proved longer than initially understood. Health officials initially believed cases began in August 2025, but later identified cases dating back to December 2023. Outbreak response was complicated by delays in removing recalled formula from store shelves and reported lags in the FDA sharing product distribution information with state food safety officials. The FDA issued warning letters to four major retailers in December 2025 for failing to promptly pull the product.
All ByHeart Whole Nutrition Infant Formula products were recalled. Although ByHeart represented approximately one percent of infant formula sales in the United States, the brand’s premium organic positioning gave it a loyal consumer base, and the outbreak broadly shaken public confidence in formula safety. Recalled product was also distributed internationally, with shipments tracked to more than 20 countries.
Root Cause Investigation Reveals Complex Contamination Pattern
The root cause investigation remains open. In January and February 2026, the FDA announced that whole genome sequencing had linked Clostridium botulinum isolates found in organic whole milk powder — supplied to ByHeart through Dairy Farmers of America, the processor for Organic West Milk — to clinical and product isolates from the outbreak. Testing has identified 17 distinct strains of the bacteria across patients, finished products, and ingredients, adding complexity to efforts to pinpoint a single contamination source. ByHeart, in a statement to the outlet that first reported the new severity data, said its root cause investigation remains ongoing.
This infant botulism outbreak has exposed gaps in surveillance, recall execution, and inter-agency communication. The new severity data reinforce that the burden of this event extended far beyond acute hospitalization, with families navigating months of follow-up care for affected infants. The findings also highlight the importance of robust post-outbreak surveillance and outcome tracking, particularly when the affected population includes the most vulnerable patients.
Sources and further reading:
Severity of Illness and Clinical Outcomes of Infants Linked to an Infant Botulism Outbreak Caused by Powdered Infant Formula — United States, 2025 – U.S. Centers for Diseases Control and Prevention
Many babies sickened in ByHeart formula botulism outbreak needed more treatment after hospitalization – Healthbeat
Outbreak Investigation of Infant Botulism: Infant Formula (November 2025) – U.S. FDA