The multistate infant botulism outbreak linked to ByHeart Nutrition infant formula has been declared over with 28 confirmed cases and 20 probable cases.

Originally, 51 cases were under investigation as part of the outbreak, but three previously reported cases from three states were ultimately diagnosed with illnesses other than infant botulism and were therefore excluded from the case count.

Extensive WGS Evidence Connects ByHeart Formula, Ingredients, and Illnesses

As of February 26, whole genome sequencing (WGS) analysis conducted by the U.S. Food and Drug Administration (FDA) and state public health partners as part of this outbreak investigation has identified 17 different strains of Clostridium botulinum in samples from patients, finished products, and ingredients.

First C. botulinum Cluster

Testing and WGS analysis conducted by FDA have matched two C. botulinum Type A isolates from one lot of organic whole milk powder to a previously identified cluster of product and clinical isolates. The two new isolates were collected by FDA at Dairy Farmers of America, the processor for Organic West Milk, which is a ByHeart supplier.

In addition to the newly identified isolates, the C. botulinum outbreak cluster includes:

• One closed powdered infant formula sample (tested by ByHeart)
• One closed powdered infant formula sample (tested by the New York State Department of Health, Wadsworth Laboratory)
• One clinical isolate
• Three isolates from one lot of organic whole milk powder (tested by ByHeart).

Second and Third C. botulinum Clusters

Additionally, WGS has shown that two clinical isolates collected and recently analyzed by the California Department of Public Health (CDPH) match clusters of isolates from product samples.

The first of these clinical isolates matches a cluster that now includes:

• Three clinical isolates
• An open powdered infant formula sample (tested by CDPH and previously reported as confirmed positive on November 18, 2025).

The second recently analyzed clinical isolate matches a cluster that now includes:

• One clinical isolate
• Four isolates from one lot of powdered infant formula (tested by ByHeart and previously reported by FDA on January 23); this lot was reported by one patient
• One sample of base mix used to make powdered infant formula (tested by ByHeart).

Root Cause Still Under Investigation; Post-Incident Updates Forthcoming

While the myriad confirmatory sample results add to the available evidence needed to investigate the root cause of this outbreak, due to the complexities of C. botulinum and limited scientific evidence currently available, FDA has not yet determined the root cause(s). Additional sample analysis and research is being conducted to inform possible conclusions about the root cause of this outbreak.

This outbreak is no longer ongoing, and FDA is transitioning from its initial response activities, managed by FDA’s Office of Coordinated Outbreak Response, Evaluation, and Prevention (CORE+EP), which focused on containing the event so that no additional illnesses occurred. The agency is now focused on post-incident response actions and activities, which may include additional surveillance, as well as prevention and compliance activities.

FDA will continue investigating the root cause(s), and future updates will be reported through FDA’s webpage, “FDA's Actions to Respond to Clostridium botulinum Illnesses Associated with Consumption of Powdered Infant Formula.” This webpage will be updated with information on FDA’s ongoing efforts to ensure the safety of powdered infant formula, including general information about formula safety.

FDA Announces New Formula Resources for Families Under ‘Operation Stork Speed’

FDA has also announced an update to its infant formula web-based resources as a deliverable of the Operation Stork Speed initiative.

The website updates include a redesign and modernization of FDA's infant formula web pages to make information more accessible and user-friendly through:

• An updated and redesigned infant formula homepage
• Several new, specific web pages outlining advancements under Operation Stork Speed
• A new, publicly accessible list of all infant formulas that are available in the U.S. market.