Legionnaires Disease

About Legionnaires Disease

Legionnaires disease was first identified in July 1976 when 182 people fell ill and 29 died after attending an American Legion convention at the Bellevue Stratford Hotel in Philadelphia. The outbreak caused panic and intense media attention. The CDC investigated for months before identifying the causative agent, a previously unknown bacterium later named Legionella pneumophila. The bacterium thrives in warm water systems including cooling towers, hot tubs, and decorative fountains. It is transmitted through inhaled water droplets, not person to person. The hotel air conditioning cooling tower was the likely source. Legionnaires disease is now recognized as a common cause of atypical pneumonia, with CDC estimates suggesting roughly 10,000 or more cases annually in the US, many of them undiagnosed. The 1976 outbreak demonstrated that unknown pathogens could cause sudden epidemics and that the CDC needed strengthened epidemic investigation capabilities. The discovery also led to new regulations for water system maintenance.