Los Angeles health officials identify legionella bacterium but say flu contracted by three guests is possible cause of outbreak

Health inspectors have found a possible source of illness among guests at Hugh Hefner's Playboy mansion in Los Angeles: bacteria in the hot tub.

More than a 100 people fell ill after the fundraising party in February, reporting pneumonia and flu-like symptoms. Officials contacted 439 people who attended the event and found 123 had fallen sick with symptoms including fever, headache, cough, shortness of breath and aches. Sixty-nine people fell sick on the day of the party. Three tested positive for H1N1 flu.

The Los Angeles health department took samples from the water in the hot tub and identified the legionella bacterium which can cause the potentially fatal legionnaires' disease.

Investigators used Twitter and Facebook to trace guests, who travelled to the fundraiser for DomainFest, a conference for internet investors from 30 countries.

Officials say the bug in the pool may not be the cause of the outbreak. In a statement the Los Angeles County department of public health said: "Though legionella bacteria was identified in a water sample taken from the Playboy Mansion, this bacteria has not been determined as the source of the respiratory outbreak.

"Other potential causes under investigation include influenza, as three individuals who attended the conference tested later positive for the flu."

The news comes at an awkward moment for Hefner. In June the 84-year-old Playboy founder is set to marry Crystal Harris, 24, Playboy Playmate of the month in December 2009. Hefner and Harris are set to appear in a pre-wedding spread in the magazine. Hefner told US Weekly: "June is a big month – Crystal and I will be in London opening a new club, then we'll come back and get married at the mansion. It's going to be a very special year. It's the Chinese year of the rabbit, so the bunny is back."