Flushing of stagnant premise water systems after the COVID-19 shutdown can reduce infection risk by Legionella and Mycobacterium spp

Abstract

The unprecedented widespread closing of buildings due to the COVID-19 pandemic has allowed water to stagnate in premise plumbing systems, creating conditions that may facilitate the growth of opportunistic pathogens. In this study, we flushed and collected samples from showers in buildings that had been unoccupied for approximately two months and quantified Legionella pneumophila using a commercial cultivation-based assay. In addition, all bacteria, Legionella spp., L. pneumophila, L. pneumophila serogroup 1, non-tuberculous mycobacteria (NTM), and Mycobacterium avium complex (MAC) were analyzed using quantitative PCR (qPCR). Despite low or negligible total chlorine in the stagnant pre-flush water samples, L. pneumophila were not detected by either method; Legionella spp., NTM, and MAC, however, were widespread. Using quantitative microbial risk assessment (QMRA), estimated risks of clinical illness from exposure to legionella and MAC via showering were generally low, but the risk of subclinical infection via Legionella spp. could exceed a 10-7 daily risk threshold if just a small fraction (≥0.1 %) of those legionellae detected by qPCR are highly infectious. Flushing cold and hot water lines rapidly restored a total chlorine (as chloramine) residual and decreased all bacterial gene targets to building inlet water levels within 30 min. Following flushing, the chlorine residual rapidly dissipated and bacterial gene targets rebounded, approaching pre-flush concentrations after 6 to 7 days of stagnation. These results suggest that stagnant water in premise plumbing may contain elevated levels of opportunistic pathogens; flushing, however, can rapidly improve water quality and reduce the health risk but the improvement will be short-lived if building disuse persists.

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

“…In comparison to free chlorine systems, chloramine systems are commonly reported to have lower L. pneumophila occurrence and concentrations, 15,68–71 even in buildings with reduced occupancy. 44 Hypothesized reasons for lower L. pneumophila occurrence in chloramine systems include that monochloramine may better penetrate biofilms, 72–75 may provide more persistent residuals in building plumbing, 76 and may more efficiently inactivate amoebal hosts or L. pneumophila within amoebae. 77,78 The few studies that examined L. pneumophila in distribution systems without a disinfectant residual generally reported low prevalence of L. pneumophila , 55,79–82 though there have been reports of L. pneumophila occurrence in some building hot water systems.…”

“…In contrast, other investigations of COVID-19 related building closures have reported that measurable disinfectant residuals were lacking in most samples. 44,48…”

“…Recent investigations into the impact of COVID-19 pandemic building closures have reported that building water quality overall was negatively impacted. 7,44–49 However, studies have reported mixed results with respect to L. pneumophila , including no detection of L. pneumophila , 44,49 no change in occurrence as water use returned to normal levels, 45 a small increase (2x) in Legionella spp. relative abundance after two months of reduced water use, 47 and widespread detection of L. pneumophila that increased during closure.…”

Critical Review: Propensity of Premise Plumbing Pipe Materials to Enhance or Diminish Growth of Legionella and Other Opportunistic Pathogens

“…Such water quality changes have been related to increased levels of OPs in premise plumbing systems [ 39 , 243 , 244 , 245 ]. In a field sampling study of main water distribution system, 120 water samples were taken throughout a drinking water distribution system.…”

A metagenomic investigation of spatial and temporal changes in sewage microbiomes across a university campus

“…Samples were collected within 1-2 weeks after students returned to on-campus residences, following a nearly stagnant and unused sewer system from March-August 2020. We hypothesized that flushing of stagnant water, lack of residual disinfectant, and idle plumbing may have contributed to changes in wastewater microbiome composition (47), with specific increases in the abundances of premise-plumbing associated pathogens such as Legionella pneumophila and Acinetobacter baumannii (48)(49)(50). For the first 5 days of the sampling period, when stagnant water was likely being flushed through the system, we found that there was an initial spike followed by a consistent decrease in the relative abundances of Legionella at 10 of the 15 sampling locations and of Acinetobacter at 7 of 15 sample locations (Figure S4).…”