WASHINGTON — The Centers for Disease Control and Prevention revealed on Friday that the infant botulism outbreak associated with ByHeart baby formula has expanded to 23 cases in 13 states. This marks an increase of eight cases since the earlier report this week.

The eight latest cases involve infants who were hospitalized and received treatment with the antitoxin BabyBIG. Michigan has now joined the list of states affected by the outbreak.

As of November 14, the outbreak encompasses infants with either suspected or confirmed cases of infant botulism, ranging in age from 16 to 200 days. All previously reported cases also involved hospitalization and the administration of BabyBIG, with no fatalities recorded.

Among the 22 infants for whom demographic data is available, 10 are female, according to the CDC. The onset of illnesses spans from August 9 to November 11.

ByHeart, a manufacturer of organic baby formula, recalled all of its products nationwide on Nov. 11. 

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.

“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. Your baby’s safety is, and always will be, our biggest priority,” ByHeart co-founders Mia Funt and Ron Belldegrun said in a letter Tuesday. 

“At this moment, the most important thing for you to know is that all ByHeart product must be discarded. We know that switching formulas is not an easy process or decision,” the co-founders added. The company has posted resources about switching infant formulas on its website. 

The FDA noted that this recall shouldn’t create shortage concerns as ByHeart infant formula products makes up less than 1% of all infant formula sold in the United States.

Prior to the recall, the FDA said infants have been hospitalized in Arizona, California, Illinois, Minnesota, New Jersey, Oregon, Pennsylvania, Rhode Island, Texas and Washington — after consuming the formula between August and November.

The U.S. Food and Drug Administration 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. U.S. Food and Drug Administration inspectors were at the Portland plant Monday, she added.

Botulism is an illness caused by a toxin that attacks the body’s nerves. It can cause difficulty breathing, muscle paralysis and death in some cases. 

The FDA says infants with botulism may experience constipation, poor feeding and difficulty swallowing, which can progress into difficulty breathing and possible respiratory arrest. Infants may also lose the ability to control their heads. 

Symptoms may take weeks to develop after getting botulism, according to the warning. 

Health officials encourage anyone with these symptoms, or who have infants experiencing these symptoms, to contact their health care provider. 

The Associated Press contributed to this report.