This story was updated at 5:27 p.m.
The Department of Correction announced late Tuesday afternoon that the six employees at Cheshire Correctional Institution treated for possible fentanyl exposure have tested negative for the drug.
Earlier in the day, the DOC said it was conducting an investigation after six employees at the prison were taken to nearby hospitals for possible exposure to the synthetic opioid. But in a subsequent statement, the agency said all of the employees tested negative for the drug and had been released from the hospital.
The state agency also said the cause of the staff illnesses “has still yet to be determined” and will continue to be investigated by the DOC and state police.
Earlier in the day, the Cheshire Fire Department tested the facility for excessive amounts of carbon monoxide in the air, and found no abnormal levels.
“I am glad that the staff members are out of the hospital,” said Department of Correction Commissioner Rollin Cook in a statement sent to reporters. “I cannot overstate how important the safety of our agency’s staff is to me.”
Prison officials called an ambulance around 9 a.m. Tuesday to transport a correctional officer to the hospital, according to a DOC press release. About an hour later, a staff member from Cheshire’s school system also began feeling unwell. Shortly after that, a school teacher and three additional correction officers also fell ill.
All of the affected staffers remained conscious and alert, the DOC said.
No inmates have exhibited signs of fentanyl exposure, the press release notes.
The state police hazmat team and the Department of Energy and Environmental Protection have since reported to the Cheshire prison, which has been placed on lockdown status.
The DOC declined to say why officials believed fentanyl was involved, stating that the matter is still under investigation.