Astronauts and NASA flight surgeons overwhelmingly dismissed reports of a crewmember flying drunk, although they did confirm a single incident of an astronaut seemingly inebriated a few days before liftoff, an employee survey released on Wednesday showed.

The single isolated incident was "an apparent interaction between prescription medication and alcohol," Ellen Ochoa, a former astronaut who now serves as the deputy director of the Johnson Space Center in Houston, told reporters on a conference call.

The incident was not considered to represent a flight risk, Ochoa said, adding that further information was not being released to protect medical privacy.

NASA chief Michael Griffin ordered the anonymous surveys after an independent panel of experts studying astronaut mental health issues reported anecdotes of astronauts being drunk on launch day and before flying an airplane.

The panel was convened in the wake of the arrest of astronaut Lisa Nowak, who faces charges stemming from a midnight attack on a romantic rival in a parking lot at Orlando International Airport last February.

"It is near impossible to predict with any reliability actions of that nature, but I think we're better off than we were a year ago," said Richard Williams, chief health and medical officer at NASA headquarters in Washington.

The anonymous Web-based surveys were taken by 87 of NASA's 98 current astronauts and all 31 of its flight surgeons between August and December 2007.

"Overall, it showed good levels of trust and healthy communications," Ochoa said.

The results painted a different picture of astronauts' rapport with flight surgeons than what the Astronaut Health Care System Review Committee, headed by Air Force Col. Richard Bachmann, found, including the anecdotes of astronauts drinking on launch day.

The Bachmann report, for example, found that astronauts were intimidated about raising medical concerns out of fear it could jeopardize their flight assignments.

NASA said it continued to foster better internal communications.

"We think of the humans as one of the critical systems on board the spacecraft," Ochoa said. "You need to have trust, you need to have good communication between astronaut and flight surgeons to make sure any medical issues are addressed."