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

William J Rhoads,Marc A Edwards,Amy Pruden

doi:10.3390/pathogens5010029

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.

Highlights

Legionella pneumophila is the most frequently reported causal agent of waterborne disease outbreaks in developed countries, causing a respiratory infection known as Legionnaires’ disease or Pontiac Fever [1,2].Inhalation of Legionella-entrained aerosols is the primary exposure pathway for infection, rather than ingestion, which is the infection route for traditional fecal pathogens that are the primary basis of water regulations [3,4,5]
Thereafter, regrowth and occurrence of and on other physicochemical trends including chlorine, ammonia, and total organic carbon (TOC) are other ecologically relevant microorganisms is examined as a function of waterand use Legionella patterns and presented
The discussion is focused on behavior of target organisms measured and other ecologically relevant microorganisms is examined as a function of water use patterns in and water flushed from the system, this is theissource of consumer exposure, butorganisms biofilm results are convective mixing

Summary

Introduction

Legionella pneumophila is the most frequently reported causal agent of waterborne disease outbreaks in developed countries, causing a respiratory infection known as Legionnaires’ disease (a severe and life-threatening pneumonia) or Pontiac Fever (a milder flu-like illness that is usually self-limiting) [1,2].Inhalation of Legionella-entrained aerosols is the primary exposure pathway for infection, rather than ingestion, which is the infection route for traditional fecal pathogens that are the primary basis of water regulations [3,4,5]. Legionella pneumophila is the most frequently reported causal agent of waterborne disease outbreaks in developed countries, causing a respiratory infection known as Legionnaires’ disease (a severe and life-threatening pneumonia) or Pontiac Fever (a milder flu-like illness that is usually self-limiting) [1,2]. L. pneumophila serogroup 1 is estimated to have caused 84% of the 6868 reported cases of legionellosis in the United States between 2009–2010, and is thought to be the most common strain associated with disease [1,2,6,7]. Nearly half of 68 cold drinking water taps were positive for L. pneumophila genetic markers (272 total samples, from 25 states across the U.S.) [10]. Hot water systems are a key reservoir for Legionella and source of disease, due to ideal growth temperatures along with dissipation of chemical

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Conclusion