The Federal Bureau of Prisons (BOP) reported 599 confirmed cases of COVID-19 at the federal prison facility in Lompoc on Thursday.
This comes after the prison began testing all of the inmates in the low-security unit of the complex this week.
According to the BOP website, a total of 574 inmates have tested positive for the virus. Another 25 staff members have also tested positive.
Officials say two inmates at the prison have died as a result of COVID-19.
Oliver Boling, 66, died on April 17 and Jimmie Lee Houston, 75, died on May 6. Prison officials said both had long-term, pre-existing medical conditions.
The prison was set to open a newly constructed "hospital care unit" on prison grounds Wednesday. It will be used to treat ill inmates who would normally require outside hospitalization.
Both Boling and Houston died at outside hospitals.
Prison officials have said, in addition to other social distancing measures to prevent spread of the virus, inmates have been restricted from using telephone and email stations. They are encouraging friends and family members of inmates to instead correspond by sending letters through the mail.