Pinpointing drivers of widespread colonization of Legionella pneumophila in a green building: Roles of water softener system, expansion tank, and reduced occupancy

Abstract

IntroductionLegionella pneumophila is an opportunistic pathogen that is a key contributor to drinking water-associated disease outbreaks in the United States. Prolonged water stagnation periods in building plumbing systems due to low occupancy, especially during building shutdowns, breaks, and holidays, can lead to water quality deterioration and (re)colonization of buildings with L. pneumophila. Water monitoring in buildings typically relies on grab samples with small datasets.MethodsIn this study, a larger dataset was created by sampling a Leadership in Energy and Environmental Design (LEED)-certified data-rich commercial building for L. pneumophila and physical-chemical water quality during the COVID-19 pandemic after reduced building occupancy. A proxy for human occupancy rates using WIFI logins was recorded throughout the study period.ResultsL. pneumophila was observed in grab samples taken throughout the building, where concentrations generally increased with greater distances from the building point of entry to locations throughout the building. Factors conducive to microbial growth were identified in the building including fluctuations in water temperatures, lack of chlorine residual, a low water heater setpoint, colonized water-saving fixtures, prolonged stagnation throughout the building; especially in an expansion tank designed to reduce pressure issues during demand fluctuations, and the presence of oversized softener tanks with ion exchange resin that contributed to chlorine residual removal as well as colonization of the resin with L. pneumophila.DiscussionFlushing and thermal disinfection alone did not resolve the problem, and replacement of the expansion tank ultimately resolved the L. pneumophila issue. As ad-hoc approaches are logistically- and time-intensive, more proactive approaches are needed for informing preventative and corrective actions for reducing the risk of exposure to opportunistic pathogens in the building plumbing.

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

“…Building AZ-1 (Legiolert positivity: 100% [ n = 7 of 7]; qPCR positivity: 100% [ n = 7 of 7]) uses a whole-building water softening system that treats water upon entry into the building. Samples collected from the water entry point revealed that the inlet water was Legiolert-negative and contained a chlorine residual of 0.59 mg L −1 as Cl 2 , 53 whereas the sample from the water storage tank immediately after the softener was positive for L. pneumophila by both Legiolert (10 616 MPN L −1 ) and qPCR (650 gc L −1 ) and had a low chlorine residual (0.05 mg L −1 as Cl 2 ). These results indicate that residual disinfectant loss was occurring in the water softener and storage tank.…”

“…34 Investigations into the impact of COVID-19 pandemicrelated building closures have reported that building water quality overall was negatively impacted. [45][46][47][48][49][50][51][52][53] However, studies have reported mixed results with respect to L. pneumophila, including no or low detection of L. pneumophila, 45,50,52 no change in the occurrence of L. pneumophila as water use returned to normal levels, 46 a small increase (2×) in Legionella spp. relative abundance after two months of reduced water use, 48 and widespread detection of L. pneumophila that increased during closure.…”

“…Site-specific investigations were conducted at several of the sampling locations, the results of which are reported elsewhere. [51][52][53]56,57 This study presents a cross-sectional analysis of potential L. pneumophila exposure risks in buildings with diverse uses, plumbing configurations, operation, and climate regions.…”

Water quality trade-offs for risk management interventions in a green building

“…L. pneumophila has been identified in green buildings as a high concern. [10][11][12] While microbial risks often drive water safety considerations due to their acute effects, chemical constituents are also important health concerns. Small diameter pipes and low flow fixtures potentially accelerate the accumulation of both chemical and microbial contaminants and can promote biofilm growth in premise plumbing.…”

Residential Water Softeners Release Carbon, Consume Chlorine, and Require Remediation after Hydrocarbon Contamination

“…In multiple Italian hotel buildings, soft water was correlated with L. pneumophila levels . Elsewhere, building water softeners reduced disinfectant residual concentration and contributed to increased faucet L. pneumophila and disinfection byproduct levels. − Resins can exert a free chlorine demand . The regeneration process can decrease microorganism concentrations, and pathogenic bacteria can remain in the softener even after regeneration .…”