Assessment of relative potential for Legionella species or surrogates inhalation exposure from common water uses

- Legionella are important waterborne pathogens in terms of mortality and occurrence.
- Assessed inhalation exposure quantitatively from six common in-home water uses.
- Developed pathway-specific emission and exposure factors for 1-day adult exposure.
- Estimated highest dose for humidifiers, shower, faucet, toilet and therapy pool.
- Determined pathways epidemiologically associated had highest estimated doses.

The Legionella species have been identified as important waterborne pathogens in terms of disease morbidity and mortality. Microbial exposure assessment is a tool that can be utilized to assess the potential of Legionella species inhalation exposure from common water uses. The screening-level exposure assessment presented in this paper developed emission factors to model aerosolization, quantitatively assessed inhalation exposures of aerosolized Legionella species or Legionella species surrogates while evaluating two generalized levels of assumed water concentrations, and developed a relative ranking of six common in-home uses of water for potential Legionella species inhalation exposure. Considerable variability in the calculated exposure dose was identified between the six identified exposure pathways, with the doses differing by over five orders of magnitude in each of the evaluated exposure scenarios. The assessment of exposure pathways that have been epidemiologically associated with legionellosis transmission (ultrasonic and cool mist humidifiers) produced higher estimated inhalation exposure doses than pathways where epidemiological evidence of transmission has been less strong (faucet and shower) or absent (toilets and therapy pool). With consideration of the large uncertainties inherent in the exposure assessment process used, a relative ranking of exposure pathways from highest to lowest exposure doses was produced using culture-based measurement data and the assumption of constant water concentration across exposure pathways. In this ranking, the ultrasonic and cool mist humidifier exposure pathways were estimated to produce the highest exposure doses, followed by the shower and faucet exposure pathways, and then the toilet and therapy pool exposure pathways.

Conceptual model for inhalation exposure assessment of Legionella species from common water uses. The human water uses representing the exposure pathways for which sufficient data were identified to quantify aerosolization and the resulting exposure doses for the adult receptor.106