The U.S. Centers for Disease Control and Prevention (CDC) has declared the infant botulism outbreak caused by Byheart infant formula to be over.
Initially it was thought there were 51 patients, but further review revealed that three of the babies were sick from other causes. This brings the total number of cases to 48 across 17 states from coast to coast. All 48 infants were hospitalized, but no one died.
Most of the babies became ill between August and November 2025, but investigators found at least one patient developed the disease in March 2022. A related company, Byheart, began selling powdered infant formula in December 2023.
Laboratory testing detected botulinum neurotoxins types A and botulinum C in an opened container of formula associated with one infant. Whole genome sequencing identified a genetic match between bacteria isolated from infant stool samples and ByHeart powdered formula products, strengthening evidence for a common cause.
Investigators also identified atypical geographic patterns of toxoid types, including rare Type A cases in some parts of the country where Type B disease typically predominates. It’s another sign that’s prompted federal and state agencies to treat the situation as a multistate outbreak, the Center for Infectious Disease Research and Policy said.
The California Department of Public Health (CDPH), Infant Botulism Treatment and Prevention Program (IBTPP) was the first agency to confirm the outbreak. The Food and Drug Administration (FDA) assisted CDC and California officials in investigating the outbreak.
The FDA found that two isolates from a lot of organic whole milk powder used to produce ByHeart infant formula matched two isolates from a lot of organic whole milk powder collected and analyzed by the FDA. This was found to be consistent with a cluster of isolates reported by the FDA on January 23, 2026, through whole genome sequencing (WGS) analysis. These two new isolates were collected by the FDA from Dairy Farmers of America, the processor of Organic West Milk, which supplies ByHeart. This cluster now also includes:
- One (1) sample of closed powder infant formula tested by ByHeart;
- One (1) sample of closed powdered infant formula tested by the New York State Department of Health Wadsworth Laboratory;
- One clinical isolate;
- These are the three ingredients isolated from one lot of organic whole milk powder tested by ByHeart.
Additionally, WGS analysis of clinical isolates revealed that two recently analyzed clinical isolates collected and analyzed by CDPH matched the cluster of isolates in the product samples.
One clinical isolate currently corresponds to a cluster that includes:
- three clinical isolates and
- Open powdered infant formula sample (tested by CDPH and previously reported as confirmed positive on November 18, 2025)
The second recently analyzed clinical isolate is consistent with a cluster that currently includes:
- One clinical isolate;
- Four substances isolated from one lot of powdered infant formula tested by ByHeart and previously reported in the FDA’s January 23, 2026 update. This lot was reported by one patient;
- One (1) sample of the base mix used to make infant formula powder tested by ByHeart
According to the FDA, detecting Clostridium botulinum in infant formula or ingredients is complex. To date, 17 strains of this bacterium have been identified in patient samples, finished products, and ingredients through WGS analysis.
“These sample results add to the evidence needed to investigate the root cause of this outbreak, but due to the complexity of Clostridium botulinum and the limited scientific evidence currently available, FDA has not yet determined the root cause. Additional sample analysis and studies are being conducted and are needed to inform possible conclusions about this outbreak,” according to the FDA.
