L.A. public health officials are trying to determine the source of an illness that they say struck dozens of conference attendees who attended an event at the Playboy Mansion earlier this month.

People who attended the conference, which included a Feb. 3 fundraiser at Hugh Hefner's Holmby Hills mansion, later complained of respiratory problems, flu-like symptoms and pneumonia. Officials have not determined the cause, but some of those who became ill said their doctors had said their symptoms stemmed from legionellosis, or Pontiac fever.

A milder form of Legionnaires' disease, legionellosis is caused by a bacterium that grows in warm water and can take root in hot tubs or parts of air-conditioning systems, according to the Centers for Disease Control and Prevention. The bacteria are not spread from person to person, according to the CDC, but are instead inhaled in water vapor. Some of those who became ill said they suspected a fog machine that was used at the party.

David Castello, 54, who co-founded Castello Cities Internet Network Inc. with his brother Michael, said they attended the conference and fundraiser. Castello told the Los Angeles Times he became ill a day after the event.