MADISON, Wis. -

Federal and state health officials said a multistate outbreak of salmonella bacteria that is resistant to several drugs has been linked to infected dairy bull calves purchased in Wisconsin.

The Centers for Disease Control and Prevention said 21 people have been infected in eight states from Jan. 11 through Oct. 24. Eight of the 21 people sickened were hospitalized, but no deaths have been reported.

Those who were sickened ranged in age from 1 year to 72. Wisconsin has the most cases with 12 people infected in eight counties.

State Veterinarian Paul McGraw is urging dairy farmers to take precautions to protect people who work closely with animals.

Symptoms of salmonella infection include diarrhea, fever and abdominal cramps.

The CDC said its investigation identified dairy bull calves from livestock markets in Wisconsin as the likely source of infections. Minnesota and South Dakota each have two cases and California, Iowa, Idaho, Missouri and Oklahoma each have one.