A bartender at a hot New York City celebrity nightspot had hepatitis A, the Health Department confirmed Friday — and was working the same night that Ashton Kutcher held his star-studded birthday party there earlier this month.

The New York City Health Department confirmed it notified patrons of Socialista of the exposure on Feb. 7, Feb. 8 and Feb. 11 and urged them to get a hepatitis A vaccination as a precautionary measure.

Kutcher was joined by dozens of celebrities at Socialista on Feb. 7 to celebrate his birthday, MyFoxNY.com reported. While the Health Department could not confirm exactly who was there, TMZ reported that Madonna, Gwyneth Paltrow, Salma Hayek and Bruce Willis were among the guests.

Click here for the MyFoxNY report and to see a photo of Kutcher leaving the nightspot on Feb. 7.

Bartender-to-Celebrity Transmission of Hepatitis A Possible

Bar owners estimate roughly 700 to 800 people may have partied at Socialista on those three nights; no additional cases of illness have been identified.

"We are asking these bar patrons to get this vaccination as a precautionary measure," Sharon Balter, a Health Department official, told MyFoxNY. "If people experience symptoms, they should see a doctor, but for most people bed rest and avoiding alcohol are all that is needed to recover. This incident serves as an important reminder to always wash hands thoroughly and regularly to prevent the spread of disease."

Video: Celebrity Hepatitis Scare

Click here to read more on this story in TMZ.

Hepatitis A is a liver disease caused by a virus that is spread by putting something in one's mouth (even though it might look clean) that has been contaminated with traces of fecal matter from an infected person, according to the Health Department.

Symptoms include jaundice (yellowing of eyes and skin), fatigue, abdominal pain, nausea and diarrhea. While some people who have chronic liver disease or a weakened immune system could experience more severe illness and require hospitalization, hepatitis A very rarely is fatal (fewer than 1 percent of cases).

FOX News' Caroline Cooney contributed to this report.