The Cook County Sheriff's Office reported that 64-year-old Karl Battiste died at Stroger Hospital on Sunday.
Battiste's cause of death is pending autopsy, the county sheriff's office said.
Just one week ago, county officials reported the death of Cook County Jail detainee Nicholas Lee. The 42-year-old also died at Stroger Hospital.
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The other detainees who died after testing positive for COVID-19 are 51-year-old Leslie Pieroni and 59-year-old Jeffrey Pendleton.
There are 395 Cook County Jail detainees who have contracted COVID-19, according to county data reported Sunday. Of the nearly 400 cases, 215 detainees are currently positive for the virus, while 180 are no longer positive.
The detainees who are no longer positive are being monitored at a recovery facility at the jail.
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Meanwhile, 191 correctional officers are confirmed to be infected, as well as 34 Cook County Sheriff's employees.
The county sheriff's office said 79 employees who previously tested positive are now recovered and have returned to work.