MARIN COUNTY, Calif. -- Approximately 800 minimum-security inmates were under quarantine at San Quentin State Prison Thursday due to four probable cases of H1N1 influenza, California Prison Health Care Services announced.

Prison officials said while there are four probable cases, 30 inmates have shown potential symptoms of the virus and have been tested.

Health officials recommended that the California Department of Corrections and Rehabilitation quarantine the areas where the infected inmates are housed. That area includes four dormitory blocks, affecting approximately 800 inmates.