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Water heater temperature set point and water use patterns influence Legionella pneumophila and associated microorganisms at the tap.

Rhoads WJ, Ji P, Pruden A, Edwards MA - Microbiome (2015)

Bottom Line: For example, at 51 °C, planktonic L. pneumophila in recirculating lines was reduced by a factor of 28.7 compared to 39 °C and was prevented from re-colonizing biofilm.We subsequently explored relationships among L. pneumophila and other ecologically relevant microbes, noting that elevated temperature did not have a general disinfecting effect in terms of total bacterial numbers.We documented the relationship between L. pneumophila and Legionella spp., and noted several instances of correlations with Vermamoeba vermiformis, and generally found that there is a dynamic relationship with this amoeba host over the range of temperatures and water use frequencies examined.

View Article: PubMed Central - PubMed

Affiliation: Charles E. Via Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA, 24061, USA. wrhoads@vt.edu.

ABSTRACT

Background: Lowering water heater temperature set points and using less drinking water are common approaches to conserving water and energy; yet, there are discrepancies in past literature regarding the effects of water heater temperature and water use patterns on the occurrence of opportunistic pathogens, in particular Legionella pneumophila. Our objective was to conduct a controlled, replicated pilot-scale investigation to address this knowledge gap using continuously recirculating water heaters to examine five water heater set points (39-58 °C) under three water use conditions. We hypothesized that L. pneumophila levels at the tap depend on the collective influence of water heater temperature, flow frequency, and the resident plumbing ecology.

Results: We confirmed temperature setting to be a critical factor in suppressing L. pneumophila growth both in continuously recirculating hot water lines and at distal taps. For example, at 51 °C, planktonic L. pneumophila in recirculating lines was reduced by a factor of 28.7 compared to 39 °C and was prevented from re-colonizing biofilm. However, L. pneumophila still persisted up to 58 °C, with evidence that it was growing under the conditions of this study. Further, exposure to 51 °C water in a low-use tap appeared to optimally select for L. pneumophila (e.g., 125 times greater numbers than in high-use taps). We subsequently explored relationships among L. pneumophila and other ecologically relevant microbes, noting that elevated temperature did not have a general disinfecting effect in terms of total bacterial numbers. We documented the relationship between L. pneumophila and Legionella spp., and noted several instances of correlations with Vermamoeba vermiformis, and generally found that there is a dynamic relationship with this amoeba host over the range of temperatures and water use frequencies examined.

Conclusions: Our study provides a new window of understanding into the microbial ecology of potable hot water systems and helps to resolve past discrepancies in the literature regarding the influence of water temperature and stagnation on L. pneumophila, which is the cause of a growing number of outbreaks. This work is especially timely, given society's movement towards "green" buildings and the need to reconcile innovations in building design with public health.

No MeSH data available.


Related in: MedlinePlus

Overview of experimental design of replicated building plumbing systems. Two identical systems were constructed to examine the effect of water heater temperature setting and water use frequency on Legionella proliferation. One remained at 39 °C (control system) while the other was incrementally increased to 58 °C (experimental system) over 15 months. Influent water was flushed through three granular activated carbon whole-house filters (sample port Inf), a recirculating pump continuously pumped water around the return loop back to the water heater creating a completely mixed reservoir (sample port Recirc), and six replicate distal taps (three upward + three downward) were flushed at 3.8 L/min (1 gallon/min) 21 times/week, 3 times/week, and 1 times/week for a total of 36 pipes (sample ports: at end of distal pipes)
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Fig1: Overview of experimental design of replicated building plumbing systems. Two identical systems were constructed to examine the effect of water heater temperature setting and water use frequency on Legionella proliferation. One remained at 39 °C (control system) while the other was incrementally increased to 58 °C (experimental system) over 15 months. Influent water was flushed through three granular activated carbon whole-house filters (sample port Inf), a recirculating pump continuously pumped water around the return loop back to the water heater creating a completely mixed reservoir (sample port Recirc), and six replicate distal taps (three upward + three downward) were flushed at 3.8 L/min (1 gallon/min) 21 times/week, 3 times/week, and 1 times/week for a total of 36 pipes (sample ports: at end of distal pipes)

Mentions: A major limitation of field studies is the inherent complexity encountered in actual building systems, which make it difficult to pinpoint precise factors that trigger Legionella proliferation. Therefore, our objective was to conduct a controlled, replicated laboratory investigation examining the interrelationship of water heater temperature set point and distal tap use frequency on Legionella occurrence. Identical experimental and control hot water plumbing systems were constructed in which continuously recirculating pipe loops delivered water to distal taps subject to high, medium, and low water use frequency (Fig. 1). Both systems were initially acclimated for 5 months at 39 °C to establish a baseline with stable microbial communities before incrementally increasing the water heater temperature of the experimental system to 42, 48, 51, and 58 °C, while the control system was maintained at 39 °C for the duration of the 15-month experiment. Genetic markers of Legionella spp. (23S ribosomal RNA (rRNA) gene), L. pneumophila (macrophage infectivity potentiator (mip) gene), Vermamoeba vermiformis (18S rRNA gene; an important ecological host for Legionella), and total bacteria (16S rRNA gene) were tracked by quantitative polymerase chain reaction (q-PCR) to measure re-growth in the recirculating lines relative to the influent water and in distal taps relative to the recirculating lines (Fig. 1). Given the current trend towards “green” buildings that are intended to conserve both water (i.e., to decrease water use frequency, which increases corresponding stagnation) and energy (i.e., lower temperature settings), the present moment is critical for untangling the complexities that trigger Legionella growth and identifying practical solutions for their control that can be considered in building system design.Fig. 1


Water heater temperature set point and water use patterns influence Legionella pneumophila and associated microorganisms at the tap.

Rhoads WJ, Ji P, Pruden A, Edwards MA - Microbiome (2015)

Overview of experimental design of replicated building plumbing systems. Two identical systems were constructed to examine the effect of water heater temperature setting and water use frequency on Legionella proliferation. One remained at 39 °C (control system) while the other was incrementally increased to 58 °C (experimental system) over 15 months. Influent water was flushed through three granular activated carbon whole-house filters (sample port Inf), a recirculating pump continuously pumped water around the return loop back to the water heater creating a completely mixed reservoir (sample port Recirc), and six replicate distal taps (three upward + three downward) were flushed at 3.8 L/min (1 gallon/min) 21 times/week, 3 times/week, and 1 times/week for a total of 36 pipes (sample ports: at end of distal pipes)
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4666224&req=5

Fig1: Overview of experimental design of replicated building plumbing systems. Two identical systems were constructed to examine the effect of water heater temperature setting and water use frequency on Legionella proliferation. One remained at 39 °C (control system) while the other was incrementally increased to 58 °C (experimental system) over 15 months. Influent water was flushed through three granular activated carbon whole-house filters (sample port Inf), a recirculating pump continuously pumped water around the return loop back to the water heater creating a completely mixed reservoir (sample port Recirc), and six replicate distal taps (three upward + three downward) were flushed at 3.8 L/min (1 gallon/min) 21 times/week, 3 times/week, and 1 times/week for a total of 36 pipes (sample ports: at end of distal pipes)
Mentions: A major limitation of field studies is the inherent complexity encountered in actual building systems, which make it difficult to pinpoint precise factors that trigger Legionella proliferation. Therefore, our objective was to conduct a controlled, replicated laboratory investigation examining the interrelationship of water heater temperature set point and distal tap use frequency on Legionella occurrence. Identical experimental and control hot water plumbing systems were constructed in which continuously recirculating pipe loops delivered water to distal taps subject to high, medium, and low water use frequency (Fig. 1). Both systems were initially acclimated for 5 months at 39 °C to establish a baseline with stable microbial communities before incrementally increasing the water heater temperature of the experimental system to 42, 48, 51, and 58 °C, while the control system was maintained at 39 °C for the duration of the 15-month experiment. Genetic markers of Legionella spp. (23S ribosomal RNA (rRNA) gene), L. pneumophila (macrophage infectivity potentiator (mip) gene), Vermamoeba vermiformis (18S rRNA gene; an important ecological host for Legionella), and total bacteria (16S rRNA gene) were tracked by quantitative polymerase chain reaction (q-PCR) to measure re-growth in the recirculating lines relative to the influent water and in distal taps relative to the recirculating lines (Fig. 1). Given the current trend towards “green” buildings that are intended to conserve both water (i.e., to decrease water use frequency, which increases corresponding stagnation) and energy (i.e., lower temperature settings), the present moment is critical for untangling the complexities that trigger Legionella growth and identifying practical solutions for their control that can be considered in building system design.Fig. 1

Bottom Line: For example, at 51 °C, planktonic L. pneumophila in recirculating lines was reduced by a factor of 28.7 compared to 39 °C and was prevented from re-colonizing biofilm.We subsequently explored relationships among L. pneumophila and other ecologically relevant microbes, noting that elevated temperature did not have a general disinfecting effect in terms of total bacterial numbers.We documented the relationship between L. pneumophila and Legionella spp., and noted several instances of correlations with Vermamoeba vermiformis, and generally found that there is a dynamic relationship with this amoeba host over the range of temperatures and water use frequencies examined.

View Article: PubMed Central - PubMed

Affiliation: Charles E. Via Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA, 24061, USA. wrhoads@vt.edu.

ABSTRACT

Background: Lowering water heater temperature set points and using less drinking water are common approaches to conserving water and energy; yet, there are discrepancies in past literature regarding the effects of water heater temperature and water use patterns on the occurrence of opportunistic pathogens, in particular Legionella pneumophila. Our objective was to conduct a controlled, replicated pilot-scale investigation to address this knowledge gap using continuously recirculating water heaters to examine five water heater set points (39-58 °C) under three water use conditions. We hypothesized that L. pneumophila levels at the tap depend on the collective influence of water heater temperature, flow frequency, and the resident plumbing ecology.

Results: We confirmed temperature setting to be a critical factor in suppressing L. pneumophila growth both in continuously recirculating hot water lines and at distal taps. For example, at 51 °C, planktonic L. pneumophila in recirculating lines was reduced by a factor of 28.7 compared to 39 °C and was prevented from re-colonizing biofilm. However, L. pneumophila still persisted up to 58 °C, with evidence that it was growing under the conditions of this study. Further, exposure to 51 °C water in a low-use tap appeared to optimally select for L. pneumophila (e.g., 125 times greater numbers than in high-use taps). We subsequently explored relationships among L. pneumophila and other ecologically relevant microbes, noting that elevated temperature did not have a general disinfecting effect in terms of total bacterial numbers. We documented the relationship between L. pneumophila and Legionella spp., and noted several instances of correlations with Vermamoeba vermiformis, and generally found that there is a dynamic relationship with this amoeba host over the range of temperatures and water use frequencies examined.

Conclusions: Our study provides a new window of understanding into the microbial ecology of potable hot water systems and helps to resolve past discrepancies in the literature regarding the influence of water temperature and stagnation on L. pneumophila, which is the cause of a growing number of outbreaks. This work is especially timely, given society's movement towards "green" buildings and the need to reconcile innovations in building design with public health.

No MeSH data available.


Related in: MedlinePlus