ByHeart, a manufacturer of organic baby formula, recalled all of its products sold nationwide Tuesday, days after some batches were recalled in an expanding outbreak of infant botulism.

At least 15 babies in 12 states have been sickened in the outbreak since August, with more cases pending, according to state and federal health officials. All of the infants were hospitalized after consuming ByHeart formula, officials said. No deaths have been reported.

ByHeart officials expanded the voluntary recall from two lots announced Saturday to all products in consumers' homes and in stores. That includes ByHeart Whole Nutrition Infant Formula and Anywhere Pack pouches of powdered formula. 

"The decision to broaden our recall to all ByHeart products comes after a call with the FDA late last night, informing us that they found two more cases of infant botulism in babies that had also consumed ByHeart at some point," Mia Funt and Ron Belldegrun, the cofounders of ByHeart, said in an open  Tuesday on the company's website. 

"The FDA's investigation into infant botulism in the U.S. is still ongoing, and we feel that there are still too many unanswered questions," they said. "Your baby's safety is, and always will be, our biggest priority." 

The company sells about 200,000 cans of infant formula a month online and in stores such as Target, Walmart, Albertsons and Whole Foods, according to Dr. Devon Kuehn, chief medical officer.

Parents and caregivers who have the formula in their homes "should immediately discontinue use and dispose of the product," Kuehn said.

ByHeart said in a  it enacted the unusual recall "in close collaboration" with the U.S. Food and Drug Administration "despite the fact that no unopened ByHeart product has tested positive" for the contamination.

"It's important that you know that neither we, nor the FDA or CDC, have found Clostridium botulinum spores or toxins in any unopened can of ByHeart formula," Funt and Belldegrun said in their open letter.

The company said its recall will remain in place while the FDA investigates the cause of the botulism outbreak. At the same time, ByHeart said it will test "every batch of formula with an independent third-party laboratory—a process which has already begun," and allow access to its facilities and unopened products for the FDA and California health officials to test "without restriction."

California health officials earlier confirmed that a sample from an open can of ByHeart baby formula fed to an infant who got sick contained the type of bacteria that causes the toxin linked to the outbreak.

The FDA is investigating 84 cases of infant botulism detected since August. Of those, 36 consumed infant formula, with a more than a third who received ByHeart formula, the agency said in a statement.

"This information shows that ByHeart brand formula is disproportionately represented among sick infants in this outbreak, especially given that ByHeart represents an estimated 1% of all infant formula sales in the United States," the FDA statement said.

ByHeart produces formula powder at a plant in Allerton, Iowa, and then ships it to a site in Portland, Oregon, for canning and distribution, Kuehn said. FDA inspectors were at the Portland plant Monday, she added.

Infant botulism is a rare and serious illness that occurs in babies under age 1, whose gut microbiomes are immature. It is caused when the infants consume bacteria that contain spores that produce a toxin in the gut. Symptoms include constipation, poor feeding, drooping eyelid, weak muscle tone, difficulty swallowing and breathing problems, among others.

Babies who develop those symptoms need immediate medical attention. The sole treatment for the infection is BabyBIG, an IV medication made from blood plasma of people immunized against botulism.