Half of Deuel Vocational Institution is on lockdown this week after an outbreak of a stomach virus affected 39 prisoners.

Inmates began to come down with flu-like symptoms from the norovirus such as stomach pain, diarrhea and vomiting last Thursday. Meals have been served in cells in the infected wings, and most inmates cannot go into any of the common areas, like the cafeteria and yard.

Prison spokesman Ray Munoz said the cause of the outbreak has yet to be pinpointed. DVI, a reception center for prisoners in Northern California, moves 750 inmates in and out of the prison each week.

The same kind of stomach virus broke out at the prison in May. Some speculated the virus was sparked by rotten milk from the onsite dairy run by prisoners, but Munoz said that was never proven.

"The norovirus is out in our community," Munoz said. "It's just a fact of life."

Visitors weren't allowed in the prison last weekend and there will not be visitation this weekend. San Joaquin County Health Department wants prison employees to wait 96 hours after the last signs of the virus before the lockdown is lifted, and before visitation is open.

A few employees have also called in sick.