Three additional inmates at the San Luis Obispo County Jail have tested positive for covid-19.
All three inmates were from the same housing unit and have been isolated.
They are being treated at the jail.
The housing unit, where the infected inmates were living, has been quarantined and all 18 inmates are being tested as well as 14 staff members.
This is the jail's first outbreak since July, according to sheriff's officials.
So far, 15 inmates have tested positive for the virus, four sheriff's deputies, eight patrol deputies and six correctional deputies.