02/21/2008 AT 09:00 PM EST
It may sound like an episode of Punk'd
– but this time it's real.
Guests at Ashton Kutcher
's 30th birthday party
at the trendy New York bar Socialista are being urged to get a Hepatitis A vaccination because one of the bartenders was infected.
Among the A-listers at the Feb. 7 event: Kutcher's wife Demi Moore
, Bruce Willis
, Gwyneth Paltrow
, and Salma Hayek
The bartender also worked on Feb. 8 and Feb. 11.
"We are asking these bar patrons to get this vaccination as a precautionary measure," said Dr. Sharon Balter, medical epidemiologist at the New York City Department of Health and Mental Hygiene.