By Linwood Outlaw III -- Daily Staff Writer

WINCHESTER — Authorities have determined that a prank initiated a foul odor that caused several employees at a local Sonic Drive-In to become sick in May.

In a press release issued Wednesday, Frederick County emergency management specialist Gail Miller, the primary spokeswoman for the investigation, said officials from the Lord Fairfax Health District, Frederick County Fire and Rescue Department, U.S. Food and Drug Administration's Office of Criminal Investigations, and FBI convened on Tuesday to discuss the status of a nearly three-month investigation into what made several employees suddenly feel nauseous during their shifts.

Emergency crews initially responded to the Sonic Drive-In restaurant located on U.S. 50 on May 17 around 10 p.m. At least four employees were taken to Winchester Medical Center for treatment after complaining of feeling light-headed and nauseous. They were later released. No customers were reportedly affected, and the restaurant remained open for business.

Agencies involved with the investigation have concluded there is no evidence of "prosecutable criminal activity by the employees" at the restaurant, the press release states. After conducting a series of inspections at the restaurant, officials with the Lord Fairfax Health District also found no evidence of improper food handling, storage or preparation methods. Officials ruled out the possibilities of carbon monoxide and food poisoning early in the investigation.

"It appears that, after all of the information has been evaluated, that this incident was, most probably, caused by a 'prank' which was initiated to create a foul odor but was intended to be harmless in nature," the press release reads. "However, due to the confined area in which the prank was executed, some employees did suffer from some nausea and vomiting as a result."

A spokesman for the restaurant could not immediately be reached for comment. Officials will not investigate the matter further, and no charges in the case are pending, Miller said via telephone Wednesday afternoon. Miller said that while "there was speculation" as to who may have been responsible for the prank, no employees were formally charged.

"There just wasn't any concrete evidence to tie anyone to that claim," she said.

Miller stressed restaurant officials' willingness to work fully with the investigation.

"Sonic was very cooperative. They gave access to whatever information was needed for the investigation. ... They have really bent over backwards to accommodate this investigation," Miller said, adding the probe included "unannounced and announced visits" to the restaurant.

The area's second Sonic Drive-In recently opened at 171 Gateway Drive, off Berryville Pike, in Winchester.

* Contact Linwood Outlaw III at loutlaw@nvdaily.com