Surprises at birthday bashes are usually welcomed, but when it comes to the likelihood of a surprise infection with hepatitis A, everybody needs to do the same thing: vaccinate!

Ashton Kutcher celebrated his 30th birthday at a West Village drink and dance club, Socialista. But before the details and gossips of the party were spread, the New York City Department of Health issued an alert: all those party-people should have a shot as a precaution.

A bartender working at Socialista was infected with the condition, the health agency informed the management of the bar. He worked on February 7 (when the celebrity-studded bash took place), 8 and 11 and an estimated number of 800 people were at the club during these three nights. A vaccination is a sure means of preventing the infection, which is an inflammation of the liver. The disease is spread via direct contact with an object which may seem clean, but be bearing minuscule traces of fecal matter.

Reps for Kutcher or Demi Moore haven’t issued any comments until the moment.

Hepatitis A is extremely rarely fatal, but it does weaken the immune system, it can also produce jaundice, nausea, diarrhea or fatigue.

Among the A-list celebrities present at the birthday party, TMZ.com reported that Madonna, Gwyneth Paltrow, Salma Hayek, Bruce Willis or Kate Hudson were there. Before the partying group headed to Socialista, they were celebrating at Bowery Hotel’s Gemma, where Demi Moore hosted also a dinner for her hubby.