About 20% of the infant formula produced in the US comes from a plant on the edge of the city of Sturgis, in southern Michigan, where it’s been a presence for more than five decades. It’s owned by Abbott Laboratories and makes Similac, the country’s most popular brand. On a September morning in 2021, two US Food and Drug Administration investigators arrived for an annual inspection that was a year overdue because of the agency’s Covid-19 restrictions. When they reviewed company records, they saw evidence of Cronobacter sakazakii, bacteria that can survive for months, sometimes years, in powdered formula and cause devastating illness in infants.