In another sign that Chicago-area infections from the coronavirus’s omicron variant may be ebbing, Cook County Sheriff Tom Dart is reporting a drop in COVID-19 cases at the massive jail he runs on the city’s Southwest Side.

His office on Wednesday reported that 352 of the jail’s 5,848 detainees were “currently positive” for the virus. Those cases were 81 fewer than the count last Friday, when the jail set a pandemic record with 433 positive detainees.

Approximately 52% of the infected detainees tested positive during the jail’s intake procedure, according to the sheriff’s office.

“They contracted the virus in the community,” a statement from office spokesman Matt Walburg said. “Those individuals were immediately medically isolated to minimize the spread of the virus.”

The virus is also brought into the facility by jail personnel. As of Wednesday, 275 of the jail’s roughly 3,100 staffers were positive for COVID-19, according to Dart’s office. Those infections were among 392 current cases among sheriff’s employees, who also provide security in county courthouses and police services in several suburbs.

A big COVID outbreak in the jail at the start of the pandemic led criminal justice officials that spring to trim the jail population by more than a quarter to about 4,000. Since May 2020, however, the population has returned to its former size.

Before omicron, the peak in daily COVID-19 numbers among detainees was 370 cases on Dec. 7, 2020. Vaccines helped reduce that number to single digits through much of this past spring and summer. Even as the delta variant swept into the county in late-summer, the number of detainees with the virus did not exceed more than a few dozen per day.

Beginning in early November, however, the tally began to climb. After omicron arrived in December, it skyrocketed. Starting Dec. 31, the number of known infections among jail detainees hovered around 400.

Dart’s office says sheriff’s personnel and Cermak Health Services, a county unit under County Board President Toni Preckwinkle, ramped up testing and vaccinations long before omicron’s arrival. The office says it also shows educational videos about the benefits of the vaccines on a daily basis throughout the jail.

The sheriff’s office has reported no deaths among detainees due to COVID-19 during the omicron wave. During earlier stages of the pandemic, according to the office, 10 detainees who had tested positive for the virus died at local hospitals.

Nearly 70% of detainees and about 80% of sheriff’s employees are vaccinated, according to the office.

Those numbers compare to 70.4% of Chicago residents, ages 18-64, who are fully vaccinated and 75.5% of suburban Cook County residents in that age range who are, according to Illinois Department of Public Health figures.

Dart required jail personnel and other employees of his office to be vaccinated but he suspended enforcement of that rule because of pushback from unions.

Chip Mitchell reports out of WBEZ’s West Side studio about policing. WBEZ’s Dan Mihalopoulos contributed reporting. Follow them at @ChipMitchell1 and @dmihalopoulos.