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Pathogens 2016, 5(1), 29; doi:10.3390/pathogens5010029

Convective Mixing in Distal Pipes Exacerbates Legionella pneumophila Growth in Hot Water Plumbing

Via Department of Civil and Environmental Engineering, Virginia Tech, 1145 Perry St., 401 Durham Hall, Blacksburg, VA 24061, USA
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Author to whom correspondence should be addressed.
Academic Editor: Claudiu T. Supuran
Received: 18 January 2016 / Revised: 15 February 2016 / Accepted: 1 March 2016 / Published: 12 March 2016
(This article belongs to the Special Issue Pathogen Legionella pneumophila)
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Abstract

Legionella pneumophila is known to proliferate in hot water plumbing systems, but little is known about the specific physicochemical factors that contribute to its regrowth. Here, L. pneumophila trends were examined in controlled, replicated pilot-scale hot water systems with continuous recirculation lines subject to two water heater settings (40 °C and 58 °C) and three distal tap water use frequencies (high, medium, and low) with two pipe configurations (oriented upward to promote convective mixing with the recirculating line and downward to prevent it). Water heater temperature setting determined where L. pneumophila regrowth occurred in each system, with an increase of up to 4.4 log gene copies/mL in the 40 °C system tank and recirculating line relative to influent water compared to only 2.5 log gene copies/mL regrowth in the 58 °C system. Distal pipes without convective mixing cooled to room temperature (23–24 °C) during periods of no water use, but pipes with convective mixing equilibrated to 30.5 °C in the 40 °C system and 38.8 °C in the 58 °C system. Corresponding with known temperature effects on L. pneumophila growth and enhanced delivery of nutrients, distal pipes with convective mixing had on average 0.2 log more gene copies/mL in the 40 °C system and 0.8 log more gene copies/mL in the 58 °C system. Importantly, this work demonstrated the potential for thermal control strategies to be undermined by distal taps in general, and convective mixing in particular. View Full-Text
Keywords: Legionella pneumophila; premise plumbing; hot water; design; installation; mixing; convection Legionella pneumophila; premise plumbing; hot water; design; installation; mixing; convection
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Rhoads, W.J.; Pruden, A.; Edwards, M.A. Convective Mixing in Distal Pipes Exacerbates Legionella pneumophila Growth in Hot Water Plumbing. Pathogens 2016, 5, 29.

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