This was a well plate containing patients’ samples being tested for SARS-CoV-2 antibodies, using the CDC serologic test. (James Gathany/CDC 2020)

A dozen inmates at the Santa Cruz County Main Jail tested positive for COVID-19 last week in what authorities say is the most significant outbreak at the lockup since the start of the pandemic.

The cases came to light on Nov. 12 during routine testing using rapid tests, according to a release on Monday from Sheriff Jim Hart.

The prisoners who tested positive are either asymptomatic or have mild symptoms, and have been quarantined. Another 35-40 inmates who were exposed have been quarantined as well, the sheriff said.

The Santa Cruz County Health Services Agency is working with the jail’s medical provider to find the source of the outbreak and contact tracing is underway.

“We are committed to ensuring the safety of all 279 inmates at the main jail as well as our staff,” according to the release from the sheriff’s office.

Prisoners who are booked into the jail are tested for COVID-19 using a rapid test and are quarantined until they receive a negative test result. Inmates are also offered the COVID-19 vaccine, provided masks, given extra cleaning materials, and encouraged to socially distance. Correctional officers also go through testing and wear masks during their shifts, the sheriff’s office said.