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Controlling Legionella pneumophila in Showerheads: Combination of Remedial Intervention and Preventative Flushing

Marianne Grimard-Conea and Michèle Prévost

Article (2023)

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Résumé

Shock chlorination and remedial flushing are suggested to address Legionella pneumophila (Lp) contamination in buildings or during their (re)commissioning. However, data on general microbial measurements (adenosine tri-phosphate [ATP], total cell counts [TCC]), and the abundance of Lp are lacking to support their temporary implementation with variable water demands. In this study, the weekly short-term (3-week) impact of shock chlorination (20–25 mg/L free chlorine, 16 h) or remedial flushing (5-min flush) combined with distinct flushing regimes (daily, weekly, stagnant) was investigated in duplicates of showerheads in two shower systems. Results showed that the combination of stagnation and shock chlorination prompted biomass regrowth, with ATP and TCC in the first draws reaching large regrowth factors of 4.31–7.07-fold and 3.51–5.68-fold, respectively, from baseline values. Contrastingly, remedial flushing followed by stagnation generally resulted in complete or larger regrowth in Lp culturability and gene copies (gc). Irrespective of the intervention, daily flushed showerheads resulted in significantly (p < 0.05) lower ATP and TCC, as well as lower Lp concentrations than weekly flushes, in general. Nonetheless, Lp persisted at concentrations ranging from 11 to 223 as the most probable number per liter (MPN/L) and in the same order of magnitude (103–104 gc/L) than baseline values after remedial flushing, despite daily/weekly flushing, unlike shock chlorination which suppressed Lp culturability (down 3-log) for two weeks and gene copies by 1-log. This study provides insights on the most optimal short-term combination of remedial and preventative strategies that can be considered pending the implementation of suitable engineering controls or building-wide treatment.

Uncontrolled Keywords

Legionella pneumophila; building plumbing; flushing; chlorination; stagnation

Subjects: 1000 Civil engineering > 1000 Civil engineering
Department: Department of Civil, Geological and Mining Engineering
Research Center: CIEP - Industrial Chair on Drinking Water
Funders: Natural Sciences and Engineering Research Council of Canada
Grant number: RGPIN-2021-04341
PolyPublie URL: https://publications.polymtl.ca/54356/
Journal Title: Microorganisms (vol. 11, no. 6)
Publisher: MDPI
DOI: 10.3390/microorganisms11061361
Official URL: https://doi.org/10.3390/microorganisms11061361
Date Deposited: 15 Sep 2023 15:35
Last Modified: 31 Oct 2023 12:22
Cite in APA 7: Grimard-Conea, M., & Prévost, M. (2023). Controlling Legionella pneumophila in Showerheads: Combination of Remedial Intervention and Preventative Flushing. Microorganisms, 11(6), 1361 (21 pages). https://doi.org/10.3390/microorganisms11061361

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