Confined spaces make rich locations for a contagious illness.  Highly infectious diseases like influenza can spread like wildfire in dorms, cruise ships, health care facilities and of course prisons. 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.

San Quentin

Luis Patino, spokesman for the federal receiver who runs prison medical care, says tests have come back on four of the 30 inmates showing flu-like symptoms. The tests show a 97 percent probability that the H1N1 virus sickened the inmates, but confirmation will take 10 days. Tests are under way on the other ill inmates.

California ended visitations at all state prisons for 10 days in May after an inmate at Centinela State Prison in Imperial County became ill.

Patino says this time officials are isolating inmates only in one cellblock at San Quentin, north of San Francisco, because they know better now how the flu affects humans. 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.