Demi Moore and Aston Kutcher could be at risk of Hep A after a birthday party.

Celebrities Demi Moore, Ashton Kutcher and Madonna are among hundreds of patrons of a New York bar being urged by New York health officials to get a Hepatitis A vaccination after a bartender was found to be infected. The city health department issued a statement, warning anyone who visited Socialista in Manhattan's West Village on February 7, 8 or 11 to get a vaccination.

Local media reports said Moore hosted a 30th birthday bash for her husband Kutcher at the venue on February 7 after a star-studded dinner at Gemma restaurant.

Other celebrities reported at Socialista were Javier Bardem, nominated for a best supporting actor Oscar, Eric Dane, Rebecca Gayheart and fashion designer Roberto Cavalli.

Socialista was not immediately available for comment, nor were representatives of Moore, Kutcher or Madonna.

"Any patron who visited the establishment after 8pm on February 7th or 8th, or after 10pm on February 11th (the times the infected person worked after becoming infectious), is considered to be at risk and needs a preventive shot," the health department said.

It said the bar owners were cooperating fully and estimated between 700 and 800 people had visited the bar on those nights, but added that no cases of illness had yet been identified.

Hepatitis A is a liver disease caused by a virus and is spread from person to person by putting something in the mouth that has been contaminated with traces of faecal matter from an infected person, the department said.

Symptoms include jaundice, fatigue, abdominal pain, nausea, and diarrhoea.