The Centers for Disease Control and Prevention and other federal agencies are investigating an E. coli outbreak linked to McDonald’s Quarter Pounders, sending shares of McDonald’s down sharply. One death of an older adult in Colorado has been reported.

The Centers for Disease Control and Prevention (CDC) issued a food safety alert on Tuesday which said an E. coli outbreak linked to McDonald’s burgers has led to one death and ten hospitalizations. “Most people in this outbreak are reporting eating the Quarter Pounder hamburger at McDonald’s before becoming sick,” the alert read.