WASHINGTON - Pennsylvania is one of 15 states reporting cases in an ongoing national investigation into additional infant illnesses linked to a recalled powdered infant formula.

The Food and Drug Administration and the Centers for Disease Control and Prevention are investigating a multistate outbreak of infant botulism that may be connected to ByHeart Whole Nutrition infant formula.

A total of 31 infants across the country have been reported with suspected or confirmed illness and confirmed exposure to the ByHeart formula. All 31 infants were hospitalized, but no deaths have been reported. The infants ranged in age from 16 to 200 days.

The investigation suggests that the ByHeart formula might be contaminated with a type of bacteria known as Clostridium botulinum.

On November 8, state health officials in California detected a substance called botulinum neurotoxin in a sample from an opened can of ByHeart powdered formula that had been fed to one of the sick infants.

Further testing confirmed the presence of the Clostridium botulinum bacteria in that sample.

The FDA is also collecting and analyzing samples of unopened products as part of its inspection.

All ByHeart Whole Nutrition Infant Formula products have been recalled. This includes all unexpired cans and single serve "anywhere pack" sticks. The formula was sold online and at major retailers nationwide and was also shipped to customers outside the United States.

Despite the recall, the FDA has received reports that the recalled product is still being found on store shelves in multiple states. The FDA is working with state partners and retailers to ensure the formula is removed from sale.

Federal health officials advise parents and caregivers to stop using any ByHeart infant formula products immediately.

Infant botulism can be serious, and medical attention should be sought right away if a child given the formula shows signs of illness.

Symptoms of infant botulism can take up to several weeks to develop after the formula is consumed. These signs often begin with constipation, poor feeding, loss of head control, and difficulty swallowing.

If you still have the formula at home, officials advise keeping the container in a safe spot, labeling it as DO NOT USE, and documenting the package information in case health officials want to collect it for testing.

The states with reported cases are Arizona, California, Idaho, Illinois, Kentucky, Maine, Michigan, Minnesota, North Carolina, New Jersey, Oregon, Pennsylvania, Rhode Island, Texas, and Washington.