(CNN) An outbreak of E. coli from tainted ground beef has expanded to sicken 177 people in 10 states, the US Centers for Disease Control and Prevention said Friday.

Of those infected, 21 have been hospitalized. No deaths have been reported. Those infected range in age from younger than 1 to 84 years old, with a median age of 18.

The cases include people who've eaten the beef since March 1, the agency said, but no supplier, distributor or brand of beef has been identified.

"Traceback investigations are ongoing to determine the source of raw ground beef supplied to grocery stores and restaurant locations where ill people reported eating," the CDC said.

"Illnesses that occurred after March 29 might not yet be reported due to the time it takes between when a person becomes ill with E. coli and when the illness is reported. This takes an average of two to three weeks," the CDC said.