As health officials investigate more than 30 cases of infant botulism linked to ByHeart baby formula since August, parents who say their children were sickened with the same illness months before the current outbreak are demanding answers, too.

California public health officials last week confirmed that six babies in that state who consumed ByHeart formula were treated for botulism between November 2024 and June, up to nine months before the outbreak that has sickened at least 31 babies in 15 states.

At the time, there was “not enough evidence to immediately suspect a common source,” the California Department of Public Health said in a statement.

Even now, “we cannot connect any pre-Aug. 1 cases to the current outbreak,” officials said.

Parents of at least five babies said that their infants were treated for the rare and potentially deadly disease after drinking ByHeart formula in late 2024 and early 2025, according to reports shared with The Associated Press by Bill Marler, a Seattle food safety lawyer representing the families.

ByHeart recalled all of its products nationwide on Nov. 11 in connection with growing cases of infant botulism.

ByHeart officials last week confirmed that laboratory tests of previously unopened formula found that some samples were contaminated with the type of bacteria that leads to infant botulism.

Marler said at least three other cases that predate the outbreak involved babies who drank ByHeart and were treated for botulism, according to their families. One consumed ByHeart formula in December 2024. The other two were sickened later in the spring, he said.

An official with the U.S. Centers for Disease Control and Prevention said federal investigators were aware of reports of earlier illnesses but that efforts are focused now on understanding the unusual surge of dozens of infections documented since Aug. 1.

“That doesn’t mean that they’re not necessarily part of this,” said Dr. Jennifer Cope, a CDC scientist leading the probe. “It’s just that right now, we’re focusing on this large increase.”

Because so much time has passed and because parents of babies who got sick earlier may not have recorded lot numbers of product or kept empty cans of formula, “it will make it harder to definitively link them” to the outbreak, Cope said.

Cope and other health officials said the strong signal connecting ByHeart to infant botulism cases only became apparent in recent weeks.

Before this outbreak, no powdered infant formula in the United States had tested positive for the type of bacteria that leads to botulism, California health officials said.

The number of cases also was within an expected range.