Botulism spores are common in the environment and can be found in most foods at very low levels, said Kristin Schill, a botulism expert at the University of Wisconsin-Madison.
Healthy adults consume Clostridium botulinum spores every day without becoming sick. But babies have immature guts that may not be able to prevent the spores from germinating and growing. Once they do, the spores produce a toxin that can cause paralysis and death.
Spores can be found everywhere, including in milk, though typically at low levels, Schill said. Pasteurization doesn’t kill the germs. They can be present in the processing environment, too.