Three staff members and one inmate at the Collin County Detention Facility tested positive for COVID-19.
The four positive tests received on Tuesday were the first positive results at the jail, according to the Collin County Sheriff's Office.
Precautions were immediately implemented and additional staff is being tested.
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The inmate who tested positive is being kept in an isolated infirmary cell. The conditions of the jailers are not known.
Currently, the jail screens all new incoming inmates and monitors inmates for symptoms while checking temperatures in the housing area several times per day.
On Monday, the Texas Department of Criminal Justice announced that it would resume limited intake of inmates from county jails starting July 1. In the TDCJ system, 7,445 inmates and 1,116 employees have tested positive for COVID-19 since March.