(CNN) -- A carbon monoxide leak sickened 49 inmates at a county jail in York, Pennsylvania, with five hospitalized overnight, county officials said Thursday
Investigators suspect the heating and ventilation system in a unit housing female inmates was the source of the odorless, colorless gas. The women began showing symptoms of carbon monoxide poisoning on Wednesday evening, York County officials said in a written statement.
The affected inmates were sent to various hospitals, and five remained there until Thursday afternoon, the officials said. The women and inmates from another nearby unit were moved to different cells, and the affected unit was still closed Wednesday evening, they said.
Carbon monoxide can be released by the burning of hydrocarbons like gasoline, natural gas or propane. Symptoms of exposure include headaches, dizziness, nausea and fatigue can be mistaken for other illnesses, like the flu, the U.S. Centers for Disease Control says.
York is about 90 miles west of Philadelphia.
CNN's Dave Alsup contributed to this report.