The investigation into an incident that made several employees ill at the Sonic Restaurant on Route 50 in Winchester has been closed by investigators.

A press release from the Frederick County Fire and Rescue Department released today said investigators view the incident as a prank that "was initiated to create a foul odor but was intended harmless in nature."

"However, due to the confined area in which the prank was executed," the release states, "some employees did suffer from some nausea and vomiting as a result. Those employees were transported to Winchester Medical Center where they were treated and released."

Investigators from the U.S. Food and Drug Administration Office of Criminal Investigations, The Federal Bureau of Investigation, the Frederick County Sheriff's Office, the Frederick County Fire and Rescue Department-Emergency Management Division and the Lord Fairfax Health District met to discuss the incident on Tuesday and they determined then to close the investigation.