Hundreds of people from around the world attended the Internet conference. Victims from as far as Germany and Sweden contracted the illness.
Attendees attended a fundraiser at the Playboy Mansion in Holmby Hills on Feb. 3 after the DOMAINfest Global Conference, which was held at the Fairmont Miramar Hotel in Santa Monica.
County health officials issued a statement saying they are investigating the "suspected respiratory infection outbreak" and looking into potential sources of exposure.
The Health Department said it is still too early to tell what the outbreak may be or how it started, but many who attended the Playboy party suspect a faulty fog machine may be to blame.
"I rarely get ill. This thing beat me up so fast, " said David Castello.
Castello became seriously ill less than 48 hours after the conference wrapped up at the hotel and the final night celebration at the Playboy mansion.
One blogger posted the email the Health Department sent out to 700 people who attended the conference. Many suspect that their symptoms are related to legionellosis, a milder form of legionnaire's disease.
"Outbreaks of legionnaire's disease are not that common," said Dr. Stephen Jones of Northridge Hospital Medical Center. "We'll see just sporadic outbreaks every once in a while, usually in groups of people who have been exposed to the bacteria, usually through some kind of contaminated air conditioning system.
A Playboy representative said the Playboy Mansion is cooperating fully with the Health Department in the investigation.
City News Service contributed to this report.