Female inmates are returning to a housing unit inside York County Prison where a carbon-monoxide leak sent 49 prisoners to area hospitals last week.

The leak occurred "during HVAC replacement construction activities" by the Harrisburg-based McClure Company, according to a news release from the county.

"Based on information provided by the company, the conditions that caused the CO migration have been remediated," the news release reads. "CO levels within the facility have remained normal since shortly after the initial incident."

The leak sent the inmates and two staff members to York and Memorial hospitals Wednesday night after dozens fell ill with "flu-like symptoms" consistent with carbon-monoxide exposure.

Six were admitted for treatment. All inmates returned to the prison by Thursday afternoon.

Detectors: In light of the incident, the county will purchase portable CO detectors, said Carl Lindquist, county spokesman.

Prison guard supervisors will wear the portable units. Supervisors were selected to wear the units on their belts because they walk throughout all parts of the prison, meaning they'll get readings from all over the entire facility, Lindquist said.

The county opted not to purchase and install hardwired detectors because of cost concerns and because inmates could tamper with the devices.

"You have tampering and security issues with the hardwired units," Lindquist said. "The best solution in our case is to go with the portable units that will go all over the place."

- Reach Greg Gross at ggross@yorkdispatch.com.- Erin James may also be reached at ejames@yorkdispatch.com.