COLUMBUS (AP) — More than 20 Ohio death row inmates have tested positive for COVID-19 in an outbreak flaring up just this past week, The Associated Press has learned.

The Department of Rehabilitation and Correction confirmed the first case to the AP on July 24 but by Friday said the number had jumped to 23.

Thirteen of those inmates were tested based on their symptoms and 10 were asymptomatic and tested through contract tracing, said prisons spokesperson JoEllen Smith.

Medical staff are monitoring the inmates, who are being quarantined and isolated under the prison system’s coronavirus policy, Smith said.

The inmates are all housed at Chillicothe Correctional Institution, where the state’s death row is based. All inmates there undergo daily symptom screening, Smith said.

Ohio has about 140 death row inmates, most housed at the Chillicothe prison. No executions are scheduled for this year as the state struggles to find drugs for its lethal injection process.

Ohio’s prison system is one of the hardest-hit in the country, with more than 5,200 inmates testing positive as of Thursday. In addition, 88 inmates have died from confirmed or probable cases of the coronavirus.

Virtually all prisons have cases, but the majority have been at Marion Correctional Institution and Pickaway Correctional Institution, which has a medical wing.