Outbreaks of Legionnaires disease have been traced to the inhalation of aerosolized water containing Legionella pneumophila, often originating from cooling towers. A recent study of an outbreak in France indicates that the distance of airborne transmission of L pneumophila may be greater than previously thought. Nguyen and associates describe an outbreak of Legionnaires disease that occurred in a rural commune in France. The mortality rate was 21% among the laboratory-confirmed cases. Risk factors for Legionnaires disease included smoking, silicosis, and spending more than 100 minutes per day outdoors. The most likely source of the outbreak was a petrochemical plant that had industrial cooling towers. The strain of L pneumophila that was isolated from the plant's cooling towers, wastewater, and air samples matched all 23 clinical isolates. The Legionnaires disease attack rate was highest among residents of the commune in which the plant was located. An analysis of aerosol dispersion from the plant's cooling towers indicated that aerosols reached the patients' homes and that the dispersion extended at least 6 km from the plant.
