Abstract
Based on the data from a French outbreak of legionellosis, a probabilistic approach was developed to analyze and assess the potential role of several suspected sources of contamination. Potential dates of exposure of all cases were determined using back-calculation, using two probability distribution functions to model incubation period. A probabilistic analysis and risk assessment were then used to determine the most probable sources of contamination for each wave of the outbreak. The risk assessment was based on parameters representing emission and dispersion of Legionella: level and duration of emission; aerosol dispersion capacity; and probability of potential exposure for each patient. Four types of facilities containing the Legionella epidemic strain were analyzed: cooling towers, aerated wastewater basins, high pressure water cleaners, and car wash stations. The results highlighted the potential role of an aerated wastewater basin in the outbreak in addition to cooling towers. The role of high-pressure water cleaners and car wash stations appeared to be non-significant. This study also reveals the lack of knowledge on facility parameters that can be useful for microbial risk assessments. This type of probabilistic analysis can be used to quantitatively assess the risk for various facilities in order to manage a legionellosis outbreak.
Highlights
Potential dates of exposure of all cases were determined using back-calculation, using two probability distribution functions to model incubation period
Some species of bacteria belonging to the Legionella genus, especially Legionella pneumophila serotype 1 (Lp-1), are recognized as a cause of community-acquired and nosocomial pneumonia known as Legionnaires’ disease or legionellosis by inhalation of contaminated water aerosols [1]
Probability of Exposure to the Potential Sources of Contamination. In this part of the investigation, we examined all four facilities containing water contaminated with Lp-1 Lens and dispersing aerosols, namely cooling towers, a wastewater basin, a car wash station, and a high-pressure water cleaner
Summary
Potential dates of exposure of all cases were determined using back-calculation, using two probability distribution functions to model incubation period. A probabilistic analysis and risk assessment were used to determine the most probable sources of contamination for each wave of the outbreak. The risk assessment was based on parameters representing emission and dispersion of Legionella: level and duration of emission; aerosol dispersion capacity; and probability of potential exposure for each patient. Four types of facilities containing the Legionella epidemic strain were analyzed: cooling towers, aerated wastewater basins, high pressure water cleaners, and car wash stations. This study reveals the lack of knowledge on facility parameters that can be useful for microbial risk assessments. This type of probabilistic analysis can be used to quantitatively assess the risk for various facilities in order to manage a legionellosis outbreak. The bacteria causing legionellosis grow in natural or artificial aquatic environments with the highest levels of contamination at water temperatures between 30 and 50 ◦ C [10]
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