Role of air sampling in investigation of an outbreak of Legionnaires' disease associated with exposure to aerosols from an evaporative condenser

The transmission of Legionnaires' disease (LD) has been found to be largely due to the inhalation of infected aerosols from air conditioning cooling towers, cascades, showers, whirlpools, humidifiers, respiratory equipment and hot potable water systems. A recent series of infections was traced to the humidifiers in use in the produce sections of supermarkets. Most epidemiologic studies use shower aerosols in tracing LD causes. Although the organism Legionella pneumophila (Lp) can be identified from air sampling, this method has not been widely used in epidemiological investigations. The use of this technique could be used to confirm the role played by evaporative condensers (EC) in the transmission of Ld. In a recent outbreak in a senior citizens' facility, both the evaporative condenser and the potable hot water system were suspect. Five residents and an employee developed the disease within a two-week period in July 1988. There were common areas (dining room, lounge, etc.) on the first two floors. Living quarters, each with shower facilities, were on the upper floors. The exhaust from a newly installed EC was less than 65 feet from the air intake for the air conditioning (AC) system. A case control study (review of historical events or records) established the relationship between the illness and the dispersal of contaminated aerosols from the EC. Monoclonal antibody subtype patterns confirmed the source of the implicated strains. Aerosolized water from residential showers did not disseminate the disease organism, despite the fact that Lp was isolated from both water sources. (Consumer Summary produced by Reliance Medical Information, Inc.)