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An in-premise model for Legionella exposure during showering events
Citation:
SCHOEN, M. E. AND N. ASHBOLT. An in-premise model for Legionella exposure during showering events. WATER RESEARCH. Elsevier Science Ltd, New York, NY, 45(18):5826-5836, (2011).
Impact/Purpose:
There are four primary objectives of this work: 1. Compare predicted risk of gastrointestinal illness from sewage impacted recreational water to non-sewage impacted water using QMRA. 2. Determine for recreational water with a mixture of sources if and when a non-sewage source of pathogens may dominate illness risk. 3. Identify key uncertain pieces of information in the QMRA estimation of risk to inform future research. 4. Compare QMRA results to epidemiologic results
Description:
An exposure model was constructed to predict the critical Legionella densities in an engineered water system that might result in infection from inhalation of aerosols containing the pathogen while showering. The model predicted the Legionella densities in the shower air, water and in-premise plumbing biofilm that might result in a deposited dose of Legionella in the alveolar region of the lungs associated with infection for a 15 minute shower exposure. Processes modeled included the detachment of biofilm-associated Legionella from the in-premise plumbing biofilm during a showering event, the partitioning of the pathogen from the shower water to the air, and the inhalation and deposition of particles in the lungs. The range of predicted critical Legionella densities in the air and water was compared to the available literature. The predictions were generally within the limited set of observations for air and water, with the exception of Legionella density within biofilms, for which there remains a lack of observations for comparison. In addition, the critical density of protozoan host in the biofilm required to propagate the infectious Legionella was estimated. Sensitivity analysis of the predicted results to possible changes in the uncertain input parameters identified the pathogen air-water partitioning coefficient and the quantity of detached biofilm from in-premise plumbing surfaces as important parameters for additional data collection. Together, this evidence can help to identify critical conditions that might lead to infection derived from pathogens within the biofilms of any plumbing system from which humans may be exposed to aerosols.
