TY - JOUR
T1 - Risk-Based Critical Concentrations of Legionella pneumophila for Indoor Residential Water Uses
AU - Hamilton, Kerry A.
AU - Hamilton, Mark T.
AU - Johnson, William
AU - Jjemba, Patrick
AU - Bukhari, Zia
AU - Lechevallier, Mark
AU - Haas, Charles N.
AU - Gurian, P. L.
N1 - Funding Information:
This research was developed under Assistance Agreement No. R836880 awarded by the U.S. Environmental Protection Agency. It has not been formally reviewed by EPA. The views expressed in this document are solely those of the authors and do not necessarily reflect those of the Agency. EPA does not endorse any products or commercial services mentioned in this publication.
Publisher Copyright:
Copyright © 2019 American Chemical Society.
PY - 2019/4/16
Y1 - 2019/4/16
N2 - Legionella spp. is a key contributor to the United States waterborne disease burden. Despite potentially widespread exposure, human disease is relatively uncommon, except under circumstances where pathogen concentrations are high, host immunity is low, or exposure to small-diameter aerosols occurs. Water quality guidance values for Legionella are available for building managers but are generally not based on technical criteria. To address this gap, a quantitative microbial risk assessment (QMRA) was conducted using target risk values in order to calculate corresponding critical concentrations on a per-fixture and aggregate (multiple fixture exposure) basis. Showers were the driving indoor exposure risk compared to sinks and toilets. Critical concentrations depended on the dose response model (infection vs clinical severity infection, CSI), risk target used (infection risk vs disability adjusted life years [DALY] on a per-exposure or annual basis), and fixture type (conventional vs water efficient or "green"). Median critical concentrations based on exposure to a combination of toilet, faucet, and shower aerosols ranged from ∼10 -2 to ∼10 0 CFU per L and ∼10 1 to ∼10 3 CFU per L for infection and CSI dose response models, respectively. As infection model results for critical L. pneumophila concentrations were often below a feasible detection limit for culture-based assays, the use of CSI model results for nonhealthcare water systems with a 10 -6 DALY pppy target (the more conservative target) would result in an estimate of 12.3 CFU per L (arithmetic mean of samples across multiple fixtures and/or over time). Single sample critical concentrations with a per-exposure-corrected DALY target at each conventional fixture would be 1.06 × 10 3 CFU per L (faucets), 8.84 × 10 3 CFU per L (toilets), and 14.4 CFU per L (showers). Using a 10 -4 annual infection risk target would give a 1.20 × 10 3 CFU per L mean for multiple fixtures and single sample critical concentrations of 1.02 × 10 5 , 8.59 × 10 5 , and 1.40 × 10 3 CFU per L for faucets, toilets, and showers, respectively. Annual infection risk-based target estimates are in line with most current guidance documents of less than 1000 CFU per L, while DALY-based guidance suggests lower critical concentrations might be warranted in some cases. Furthermore, approximately <10 CFU per mL L. pneumophila may be appropriate for healthcare or susceptible population settings. This analysis underscores the importance of the choice of risk target as well as sampling program considerations when choosing the most appropriate critical concentration for use in public health guidance.
AB - Legionella spp. is a key contributor to the United States waterborne disease burden. Despite potentially widespread exposure, human disease is relatively uncommon, except under circumstances where pathogen concentrations are high, host immunity is low, or exposure to small-diameter aerosols occurs. Water quality guidance values for Legionella are available for building managers but are generally not based on technical criteria. To address this gap, a quantitative microbial risk assessment (QMRA) was conducted using target risk values in order to calculate corresponding critical concentrations on a per-fixture and aggregate (multiple fixture exposure) basis. Showers were the driving indoor exposure risk compared to sinks and toilets. Critical concentrations depended on the dose response model (infection vs clinical severity infection, CSI), risk target used (infection risk vs disability adjusted life years [DALY] on a per-exposure or annual basis), and fixture type (conventional vs water efficient or "green"). Median critical concentrations based on exposure to a combination of toilet, faucet, and shower aerosols ranged from ∼10 -2 to ∼10 0 CFU per L and ∼10 1 to ∼10 3 CFU per L for infection and CSI dose response models, respectively. As infection model results for critical L. pneumophila concentrations were often below a feasible detection limit for culture-based assays, the use of CSI model results for nonhealthcare water systems with a 10 -6 DALY pppy target (the more conservative target) would result in an estimate of 12.3 CFU per L (arithmetic mean of samples across multiple fixtures and/or over time). Single sample critical concentrations with a per-exposure-corrected DALY target at each conventional fixture would be 1.06 × 10 3 CFU per L (faucets), 8.84 × 10 3 CFU per L (toilets), and 14.4 CFU per L (showers). Using a 10 -4 annual infection risk target would give a 1.20 × 10 3 CFU per L mean for multiple fixtures and single sample critical concentrations of 1.02 × 10 5 , 8.59 × 10 5 , and 1.40 × 10 3 CFU per L for faucets, toilets, and showers, respectively. Annual infection risk-based target estimates are in line with most current guidance documents of less than 1000 CFU per L, while DALY-based guidance suggests lower critical concentrations might be warranted in some cases. Furthermore, approximately <10 CFU per mL L. pneumophila may be appropriate for healthcare or susceptible population settings. This analysis underscores the importance of the choice of risk target as well as sampling program considerations when choosing the most appropriate critical concentration for use in public health guidance.
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U2 - 10.1021/acs.est.8b03000
DO - 10.1021/acs.est.8b03000
M3 - Article
C2 - 30629886
AN - SCOPUS:85064568807
SN - 0013-936X
VL - 53
SP - 4528
EP - 4541
JO - Environmental Science and Technology
JF - Environmental Science and Technology
IS - 8
ER -