Forty-eight infants in 17 states across America were hospitalized with botulism after consuming ByHeart Whole Nutrition infant formula between late 2023 and early 2026 — the largest infant botulism outbreak ever documented in the United States. All 48 were treated with BabyBIG, the only available treatment for infant botulism. No infants died. The CDC and FDA declared the outbreak over on February 26, 2026, with no new cases reported since December 2025.
But the definitive answer to how Clostridium botulinum contaminated a commercially manufactured infant formula product — a contamination event that should be virtually impossible given the regulatory oversight applied to one of the most tightly controlled categories of food in America — remains officially undetermined. A June 10, 2026 investigation by Food Safety Magazine reveals that the FDA's completed inspections of ByHeart's facilities "did not identify any deficiencies that could explain the root cause of this outbreak" — even though whole-genome sequencing has confirmed a genetic match between C. botulinum isolated from patients, from ByHeart finished formula products, and from organic whole milk powder collected at Dairy Farmers of America, the processor for ByHeart's supplier Organic West Milk.
The gap between "we know the contamination came from this ingredient" and "we cannot explain how" is one of the most uncomfortable positions in food safety regulation — and it is where the ByHeart investigation currently stands.
How the Outbreak Was Discovered and How It Unfolded
The outbreak came to light when the California Department of Public Health's Infant Botulism Treatment and Prevention Program (IBTPP) — the single national program that supplies all BabyBIG treatment for infant botulism and therefore has visibility into every diagnosed U.S. case — detected a surge in infant botulism cases in babies who had consumed ByHeart formula. Because California's IBTPP is the only source of the antitoxin treatment in the country, it effectively functions as a passive national surveillance system for this rare disease.
The FDA announced the investigation on November 14, 2025, initiating product testing and an onsite inspection of ByHeart's facilities. ByHeart initially declined to recall. Following continued FDA requests and the identification of matching bacterial strains in formula and from patients, ByHeart recalled all of its infant formula on November 11, 2025 — a recall that affected approximately $1.5 million of product and represented the company's entire product line.
ByHeart stated the recall was done under protest, saying it disputed being the cause of the outbreak. On January 23, 2026, the FDA shared a pivotal finding: two samples of organic whole milk powder collected at Dairy Farmers of America tested positive for C. botulinum, and whole-genome sequencing confirmed a genetic match to isolates from patients and finished formula products. Two milk powder suppliers — Dairy Farmers of America and, by implication, Organic West Milk — were identified as the likely source of contaminated ingredients.
Why the Root Cause Remains Unknown — and Why It Matters
The outstanding puzzle is this: Clostridium botulinum spores are common in the environment. They are found in soil, sediment, and dust. They can enter any food manufacturing facility. But the standard safeguard for powdered infant formula is precisely the heat treatment process — spray drying — that converts liquid milk into powder. At properly controlled temperatures and conditions, this process should inactivate botulinum spores.
FDA's completed inspection of ByHeart's facilities did not identify any failures in this process. Prior inspection reports from 2023 had surfaced hygiene and food safety violations at a now-closed ByHeart production facility, and the company had received an FDA warning letter in 2023 — but FDA's outbreak investigation did not link those historical violations to the 2025 contamination event.
This leaves investigators examining the upstream dairy supply chain — specifically whether contamination occurred during the conversion of raw milk to powder, or in the sourcing of the raw milk itself, or in post-drying handling and storage. FDA is now undertaking surveillance sampling to better assess the presence of C. botulinum in powdered milk broadly, and has advocated for a formal risk assessment on spore-forming pathogens in powdered infant formula by the FAO/WHO Expert Meetings on Microbiological Risk Assessment.
ByHeart has announced a new C. botulinum-specific testing protocol that will be applied to every dairy ingredient and finished batch before release as it works with FDA to safely resume infant formula production. The formula company confirmed on June 3, 2026 that FDA's completed onsite inspections found no deficiencies — and that production resume planning is underway.
What Parents Should Know
The recalled ByHeart products should no longer be in circulation. Parents who previously purchased ByHeart formula should not use any remaining product and should contact their pediatrician if they have concerns. Infant botulism is a medical emergency — the warning signs include constipation, poor feeding, weak cry, generalized weakness, and difficulty swallowing or breathing. Any infant showing these signs requires immediate emergency care.
Frequently Asked Questions
Q: How many infants were sickened in the ByHeart botulism outbreak?
A: 48 confirmed infants across 17 states. All were hospitalized and treated with BabyBIG. No deaths were reported. The outbreak was declared over February 26, 2026.
Q: Has the root cause been identified?
A: Not definitively. Whole-genome sequencing linked the contamination to organic whole milk powder from a third-party supplier, but FDA inspections of ByHeart's facilities found no specific deficiency explaining how the contamination occurred.
Q: Is ByHeart formula still on sale?
A: ByHeart recalled all of its products in November 2025. Production has not resumed as of the most recent reporting. The company is working with FDA to implement new testing protocols before resuming.
Q: What are the warning signs of infant botulism?
A: Constipation (often the first sign), poor feeding, weak cry, decreased movement and muscle tone, difficulty swallowing, and in severe cases, breathing difficulty. Any of these symptoms in an infant require immediate emergency medical evaluation.
Q: What is BabyBIG and is it available?
A: BabyBIG (botulism immune globulin intravenous) is the only approved treatment for infant botulism. It is supplied exclusively by the California Department of Public Health's IBTPP. It must be administered promptly after diagnosis and must be requested through the program at (510) 231-7600.
