The San Luis Obispo County Sheriff's Office says five housing units at the County Jail are under quarantine because of a flu outbreak.
Nine inmates have reportedly come down with the flu since early March.
The sheriff's office says it is managing influenza cases in the jail with the help of the Public Health Department.
Four of the nine inmates who've become ill have recovered and were released from isolation, according to sheriff's officials.
Inmates are offered Tamiflu to help prevent them from getting sick, and so far, the sheriff's office says no new cases of flu have been identified in the quarantined units.
Each housing unit contains between five and 40 people and they are released from quarantine after seven days without any new cases.
As a result of the illnesses, court appearances are being conducted via video conferencing.
Sheriff's officials say each inmate entering the jail is screened and they are isolated if they show any symptoms of illness. Jail staff is also reportedly conducting extra cleaning of cells and common areas.
The sheriff's office says this is not out of the ordinary at the jail during flu season.
The illnesses are not related to the coronavirus pandemic, according to sheriff's officials. They say ill inmates who tested negative for influenza have also been tested for COVID-19 and there have been no positive results.