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Quantitative Risk Estimation for a Legionella pneumophila Infection Due to Whirlpool Use

Authors

  • Martijn Bouwknegt,

    Corresponding author
    • Laboratory for Zoonoses and Environmental Microbiology, Centre for Infectious Disease Control Netherlands, National Institute for Public Health and the Environment, Bilthoven, The Netherlands
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  • Jack F. Schijven,

    1. Expert Centre for Methodology and Information Services, National Institute for Public Health and the Environment, Bilthoven, The Netherlands
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  • Johanna A.C. Schalk,

    1. Laboratory for Zoonoses and Environmental Microbiology, Centre for Infectious Disease Control Netherlands, National Institute for Public Health and the Environment, Bilthoven, The Netherlands
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  • Ana Maria de Roda Husman

    1. Laboratory for Zoonoses and Environmental Microbiology, Centre for Infectious Disease Control Netherlands, National Institute for Public Health and the Environment, Bilthoven, The Netherlands
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Address correspondence to Martijn Bouwknegt, RIVM – CIb/LZO p.a. Martijn Bouwknegt (pb. 63), P.O. Box 1 NL-3720BA, Bilthoven, The Netherlands; tel: +31-30-2747002; fax: +31-30-2744434; martijn.bouwknegt@rivm.nl.

Abstract

Quantitative microbiological risk assessment was used to quantify the risk associated with the exposure to Legionella pneumophila in a whirlpool. Conceptually, air bubbles ascend to the surface, intercepting Legionella from the traversed water. At the surface the bubble bursts into dominantly noninhalable jet drops and inhalable film drops. Assuming that film drops carry half of the intercepted Legionella, a total of four (95% interval: 1–9) and 4.5×104 (4.4×104 – 4.7×104) cfu/min were estimated to be aerosolized for concentrations of 1 and 1,000 legionellas per liter, respectively. Using a dose-response model for guinea pigs to represent humans, infection risks for active whirlpool use with 100 cfu/L water for 15 minutes were 0.29 (∼0.11–0.48) for susceptible males and 0.22 (∼0.06–0.42) for susceptible females. A L. pneumophila concentration of ≥1,000 cfu/L water was estimated to nearly always cause an infection (mean: 0.95; 95% interval: 0.9–∼1). Estimated infection risks were time-dependent, ranging from 0.02 (0–0.11) for 1-minute exposures to 0.93 (0.86–0.97) for 2-hour exposures when the L. pneumophila concentration was 100 cfu/L water. Pool water in Dutch bathing establishments should contain <100 cfu Legionella/L water. This study suggests that stricter provisions might be required to assure adequate public health protection.

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