A salmonella-tainted salad served at a northeastern Arizona prison caused 241 inmates and three employees to become ill this month, a spokesman said on Friday.

Health officials determined lettuce or cabbage served on Aug. 31 to inmates inside two units at the Arizona State Prison Complex-Winslow was responsible, said corrections department spokesman Andrew Wilder.

"We are confident now that this wasn't a cleanliness issue and came from a product that was brought into the kitchen," said Wilder, adding that operations returned to normal last week.

Prison officials said inmates began feeling the first symptoms of the bacteria on Sept. 1 in the Kaibab unit and the next day in the Coronado unit. The illnesses continued for another five days, and three prison employees were among those who got sick, officials said.

Inmates reported suffering from nausea, diarrhea, vomiting, chills and fever and were treated at the prison, Wilder said.

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They were restricted to their housing quarters as a precaution, officials said.

Outside visitation was canceled during the busy Labor Day weekend and the units were scrubbed with bleach, and off-site work details for minimum-security inmates was halted, officials said.

No one died from the outbreak, officials said.

Normal operations at the two units, which house more than 1,400 inmates, resumed on Sept. 16, Wilder said.

Overall, the U.S. Centers for Disease Control and Prevention reports that about 1.2 million people become ill annually from salmonella, with about 450 cases resulting in death.