Officials say a staff member at a state prison in Los Angeles County has tested positive for tuberculosis.
Prison spokesman Lt. George Allen says that officials will be testing all inmates and staff at the Lancaster facility for the disease.
Allen says the testing was to begin Thursday and would continue as long as necessary.
A statement issued by state prison officials said an investigation was underway to try to identify "staff and inmates who may have had close contact" with the infected person.
Officials say no prisoners will be received or transferred out until testing is completed and visitations have been suspended for this weekend.
The Lancaster facility houses nearly 4,600 inmates and employs about 1,900 people.