The Los Angeles Times says health officials presented their findings Friday at an annual conference at the Centers for Disease Control in Atlanta.
The legionella bacteria also causes a milder illness called Pontiac fever. Symptoms include fever and headache.
Many people who attended a fundraiser party at the Playboy Mansion came down with a respiratory illness after the DomainFest conference in February.
Officials contacted 439 people and found that 123 had fevers and at least one other symptom with 69 falling ill on the same day. Epidemiologists used social media to contact the conference attendees.
