Water Stagnation and Flow Obstruction Reduces the Quality of Potable Water and Increases the Risk of Legionelloses

Abstract

Legionella is an opportunistic waterborne pathogen associated with Legionnaires' disease and Pontiac fever. Despite improved public awareness, the incidence of Legionella associated infections has been increasing. Aerosols generated from engineered potable water systems are a demonstrated cause of both nosocomial and community-acquired legionellosis. The ecology of Legionella in these systems is complex with multiple factors impacting their colonization and persistence. Flow dynamics has been identified as an important factor and stagnation in cooling towers is an accepted risk for increased Legionella growth; however, less is known about the impact of flow dynamic on Legionella in potable water systems. This is especially complex due to the inherent intermittent and variable usage observed within outlets of a potable water system. This systematic literature review examines the role of fluid dynamics and stagnation on the colonization and growth of Legionella in potable water systems. Twenty two of 24 identified studies show a positive association between stagnation zones and increased colonization of Legionella. These zones included dead legs, dead ends, storage tanks, and obstructed water flow (such as intermittent usage or flow restriction). Prolonged stagnation in building plumbing systems also deteriorates the quality of thermally or chemically treated potable water. This stimulates the colonization of Legionella established biofilms. Such biofilms are intrinsically resistant to disinfection procedures and accelerate the rate of decay of chemical disinfectants. Sub-lethal doses of disinfectants and the presence of protozoan hosts in stationary water promote generation of viable but non-culturable Legionella cells. This results in false negatives in surveillance methods that use culture methodology. In conclusion, elimination of temporal and permanent stagnation points can improve the quality of potable water, efficacy of disinfectants, and reduce the risk of legionellosis. Current guidelines and water safety plans recognize the risks associated with permanent stagnation point (dead ends and dead legs); however, there is a need for greater emphasis on controlling temporal stagnation arising from intermittent usage.

Legionella pneumophilaoccurrence in reduced-occupancy buildings in 11 cities during the COVID-19 pandemic

“…[27][28][29][30] However, few studies have investigated its occurrence during extended periods of reduced water use. 22,26,[31][32][33] The quantification of L. pneumophila levels in potable water systems has traditionally been performed using plate culture methods. However, alternative methods such as the IDEXX Legiolert ® kit, a liquid culture method that yields results in most probable number (MPN) per volume, has become more widely used in recent years due to its ease of use and reported specificity for L. pneumophila.…”

Reducing the Risk of Healthcare Associated Infections from Legionella and Other Waterborne Pathogens Using a Water Management for Construction (WMC) Infection Control Risk Assessment (ICRA) Tool

“…Improper building water distribution design and commissioning can lead to increased colonization of bacteria such as Legionella [ 1 , 13 , 19 ]. The effectiveness of temperature and disinfectant as risk mitigation strategies diminishes over time without adequate water movement [ 44 ]. During construction, the BWDS is filled with water (i.e., water activation) and may be left for weeks or months without use before the building is occupied with employees and patients [ 13 ].…”

“…Industrial Hygienists are trained to focus on engineering and work-practice controls aimed at preventing exposure before any infection is detected, practices that offer “the best possibility for prevention and control of Legionnaires’ disease” [ 54 ]. The WMC-ICRA aids the practicing industrial hygienist in these prevention efforts by providing a systematic framework for the analysis of water systems during construction activities, when the system is more vulnerable, and conditions are more ideal for pathogen propagation [ 13 , 44 ]. Although healthcare workers and construction workers have a smaller documented burden of Legionella disease than patients [ 1 ], occupational exposures and disease cases are described in the literature [ 30 , 32 , 55 ] and disease may be underreported among workers compared to patients in healthcare settings [ 52 ].…”

Combining Traditional and Molecular Techniques Supports the Discovery of a Novel Legionella Species During Environmental Surveillance in a Healthcare Facility

“…The presence of biofilm, water stagnation due to low water flow, dead branches, or old pipelines are factors that make the WDS's facilities (e.g., large public or private buildings, companies, hospitals, or health facilities) a potential risk to the dissemination of Legionella spp. (Di Pippo et al, 2018 ; Nisar et al, 2020a , b ; Totaro et al, 2020 ).…”