A third inmate at the California Men's Colony in San Luis Obispo has tested positive for COVID-19, according to the California Department of Corrections and Rehabilitation (CDCR).
Prison officials said they could not provide information on whether the three cases were connected.
The first CMC case was reported on April 11 and the second case was reported this past Wednesday.
A total of 20 inmates at the prison have reportedly been tested for the coronavirus. Sixteen were negative and the results for one inmate are still pending.
One staff member at the prison has also tested positive for COVID-19.
CDCR says it is working with local health officials to conduct contact investigations and determine if any other inmates or staff have been exposed to the virus.