Two different infant formula brands, made by different companies on different continents, sickened infants with Clostridium botulinum seven months apart. What the two products had in common was not a factory. It was an ingredient. FDA’s traceback determined that the ByHeart formula implicated in the November 2025 outbreak and the Nara Organics formula implicated in the 2026 outbreak were both made with organic whole milk supplied by Organic West Milk and spray dried into powder by Dairy Farmers of America. On August 27, 2026, the laboratory work caught up to the paperwork: whole genome sequencing showed that C. botulinumisolated from an infant sickened by Nara formula is a genetic match to C. botulinum isolated from an infant sickened by ByHeart formula, to a powdered infant formula base sample collected in the ByHeart investigation, and to four samples of unopened cans of ByHeart formula. The same organism reached babies through two brands. The only place the two supply chains overlap is upstream of both formula plants — at the milk and at the dryer.

The production point of view.

Follow the powder forward. Organic West Milk supplies raw organic whole milk. Dairy Farmers of America takes that liquid milk, and spray dries it into organic whole milk powder — the bulk dairy base that a formula manufacturer buys by the tote and blends with oils, carbohydrates, vitamins and minerals to make finished infant formula. That powder then goes to whichever formula maker bought it. In 2025 it went to ByHeart, whose formula is made in the United States. In 2025 and 2026 it also went into the Nara Organics product, which FDA says was manufactured in Europe at two firms the agency had inspected before these illnesses, issuing observations citing deficiencies to both. Two brands, two sets of formula plants, two countries of manufacture — and one shared dairy base flowing into both.

That is why the shared ingredient matters more than anything either brand did on its own canning line. A contamination event at a formula plant contaminates that plant’s product. A contamination event in the milk, or in the drying step that converts milk to powder, contaminates every downstream customer that bought from the affected production — regardless of how clean the formula plant is, whose name is on the label, or which continent the can was filled on.

Sources: FDA, Post-Outbreak Response Activities (July 13, 2026); FDA outbreak advisory updates of June 26, July 6 and August 27, 2026; CDC outbreak pages for both investigations. The two chains are identical through the dryer and diverge only after it.

Two features of this product make an upstream contamination event carry all the way to a bottle. First, C. botulinum forms spores, and FDA states plainly that spore-formers survive typical pasteurization and harsh environmental conditions — so heat treatment of the milk upstream does not remove them. Second, powdered infant formula is not a sterile product and has no terminal kill step after blending and canning; the finished powder is not retorted or otherwise treated in a way that would destroy surviving spores. Contamination that is present in the milk or introduced during drying is therefore not corrected by anything that happens later. It is packaged.

FDA has not resolved which of those two points the organism entered at. Its position on August 27 remains that there is not enough evidence to determine whether the milk was contaminated before drying or during the drying process, and its root cause investigation stays open with a focus on ingredients. That is an unresolved question between two defendants’ operations, not a gap in the link between the two outbreaks.

The laboratory point of view — what whole genome sequencing actually showed.

Whole genome sequencing reads the full DNA of a bacterial isolate. Two isolates that are indistinguishable, or separated by only a few base differences, are the same strain — which in practice means they came from the same contamination event rather than from two unrelated encounters with an organism that is common in soil and dust. It is the difference between saying two products shared a supplier and saying two products shared a contamination.

What was published in the ByHeart investigation:

• FDA’s inspections of the ByHeart facilities identified C. botulinum in a powdered milk ingredient.
• FDA and ByHeart sampled dairy ingredients at Dairy Farmers of America. Two samples from one lot of organic whole milk powder were shown by WGS to match a clinical sample and a positive infant formula sample. That is a closed chain: milk powder at the dryer, to finished formula, to a sick baby.

What FDA added on August 27, 2026:

• One clinical sample from an infant in the Nara outbreak is a genetic match to a clinical sample from an infant in the 2025 ByHeart outbreak; to a powdered infant formula base sample collected during the ByHeart investigation; and to four samples of unopened cans of ByHeart formula.

The word doing the most work there is unopened. A positive from an opened can invites the argument that a household, a scoop or a countertop introduced the organism after purchase. Sealed cans foreclose it. The strain was in the product as it left the manufacturer.

Put the two publications together and the chain runs the length of the supply. The Nara infant’s isolate matches the ByHeart infant’s isolate. The ByHeart infant’s isolate was previously reported to match organic whole milk powder sampled at Dairy Farmers of America. If the clinical sample described in the August 27 update is the same patient isolate described in the earlier one — which FDA has not stated, and which is the first thing to confirm — then the organism recovered from a baby fed Nara formula is indistinguishable from the organism recovered from a lot of milk powder at the dryer that served both brands. That is the inference the published record supports. It should be pled as an inference and confirmed with the isolate identifiers, the NCBI accessions and the SNP distances before it is stated as a fact.

Sources.

• FDA, Outbreak Investigation of Infant Botulism: Powdered Infant Formula (June 2026), updates of June 13, June 26, July 6 and August 27, 2026, https://www.fda.gov/food/outbreaks-foodborne-illness/outbreak-investigation-infant-botulism-powdered-infant-formula-june-2026.
• FDA, Post-Outbreak Response Activities: Clostridium botulinum Illnesses Associated with Consumption of Powdered Infant Formula, content current as of July 13, 2026, https://www.fda.gov/food/outbreaks-foodborne-illness/post-outbreak-response-activities-clostridium-botulinum-illnesses-associated-consumption-powdered.
• CDC, Infant Botulism Outbreak Linked to Powdered Infant Formula, June 2026, August 27, 2026, https://www.cdc.gov/botulism/outbreaks-investigations/infant-formula-june-2026/index.html.
• CDC, Infant Botulism Outbreak Linked to Infant Formula, November 2025, https://www.cdc.gov/botulism/outbreaks-investigations/infant-formula-nov-2025/index.html.