The Pennsylvania Department of Corrections has placed prisons statewide on lockdown, after a series of incidents in which correctional officers were hospitalized in connection with exposure to an unknown substance.

"The safety and security of our employees is my No. 1 concern," Corrections Secretary John Wetzel said in a statement released Wednesday. "Our state prisons, especially those in the western part of the state, have experienced recent incidents in which employees have been sickened, and we need to get to the bottom of this issue now."

That means visiting rooms are closed, non-legal mail service is suspended, and employees will be given training and personal protective gear to prevent further exposure.

"There has been one confirmed case of exposure to a synthetic cannabinoid at SCI Greene on Aug. 13," a spokesperson said in an email. "The DOC suspects the substance sickening individuals is a form of K2 but there is only that one confirmed case so far."

READ MORE: Overdose just by touching fentanyl? Highly unlikely, experts say.

Wetzel cited media reports that 24 staff and inmates at Ross Correctional Institution in Chillicothe, Ohio, were sickened Wednesday morning — and many received doses of naloxone — after contact with a substance authorities said may be fentanyl.

But whether fentanyl can actually sicken workers who come into incidental contact with it is another matter. The National Institute for Occupational Safety and Health describes fentanyl as a "potential hazard" and recommends that emergency responders use protective equipment. However, the American College of Medical Toxicology and the American Academy of Clinical Toxicology issued a position paper last year describing the risk from incidental contact to the drug as extremely low. Medical authorities have warned against "opioid hysteria," and noted that just because someone received naloxone and later recovered doesn't mean it was an appropriate treatment.

Here in Pennsylvania, state police are still working to identify what sickened at least 23 officers at the state prisons at Camp Hill, Smithfield, Fayette, Greene, and Mercer over the last month.

Six staffers were infected in a single incident Aug. 6 at Camp Hill, the DOC said in a statement. They were admitted to a hospital after searching a cell and packing an inmate's property. "All had either come into direct contact with a suspicious substance or had been in contact with someone who had contact with the substance. One employee required administration of Narcan and was admitted to the hospital," the statement noted. "Prison officials were informed that the entire hospital, including the ER, was shut down for decontamination."

The DOC noted it has uncovered several instances of suspected smuggling in past weeks.

On Aug. 21, the department outlined a series of measures in the works to improve security at the prisons.

Those include purchasing body scanning devices, expanding the K-9 unit (and purchasing special doses of the overdose-reversing drug naloxone for dogs), and updating mail-delivery procedures. One option under review would involve contracting with a third-party vendor to scan and forward all incoming mail to prevent the possible delivery of illicit substances hidden under stamps or saturated into paper.

Gov. Wolf issued a statement praising the DOC for working "diligently to address the emerging issue of synthetic drugs in our prison system. … Today's action to lock down all of the state's correctional facilities is a necessary step to ensure the safety of our officers."

The Pennsylvania State Correctional Officers Association president, Jason Bloom, said in a statement that the union was monitoring the situation.

"Corrections officers already work a very dangerous job," he said. "We expect the department to do all that it can to ensure this issue is eradicated in state prisons."

This article has been updated to include information about one confirmed case of exposure to a synthetic cannabinoid.