A ping pong ball falls into a red cup during a game of beer pong.Here’s news for party animals also concerned about trying to stay healthy: beer pong can be dirty. And gross.

A group of student researchers from Clemson University tested pingpong balls being used in beer pong in various locations around campus one weekend. They found them laden with bacteria. In addition, they determined that the balls contaminated the glasses of beer (from which contestants later drank) with organisms such as E. coli, listeria, staph and salmonella.

“It makes sense when you consider that these balls are rolling on the ground and also being used by some people whose hand hygiene may be questionable,” said Christina Leonard, MD, an infectious disease specialist at Spectrum Health Medical Group.

The basic game of beer pong involves players tossing pingpong balls into glasses of beer, then chugging the brews. The researchers studied balls from indoor and outdoor games and found the outdoor brews carried the highest level of contamination. Indoor games played on carpet produced the lowest bacterial load.

“I do not endorse drinking games, but I’d say players should certainly avoid drinking out of the cups contestants are throwing balls into. It’s a needless risk,” Dr. Leonard said. “Players could use their own individual cups of beer to avoid contamination. Or, better yet, they could just use water, keep score and not over indulge.”

For those thinking a quick removal of the ball from beer may limit their risk, the researchers took the study one step further.

In the lab they placed bacteria on balls and put the balls in glasses of beer. The transfer of bacteria to beer was surprisingly high, no matter how long those balls stayed in the glass.