Hot water plumbing in residences and office buildings have distinctive risk of Legionella pneumophila contamination

Legionella spp. is an environmental bacterium that causes the human respiratory disease, legionellosis. Legionellosis is contracted by breathing or aspirating soil or water droplets contaminated with Legionella. Legionellosis is associated with two clinical manifestations: Legionnaires' disease (severe) and Pontiac fever (mild). Legionnaires’ disease signs and symptoms are similar to pneumonia (Mandell et al., 2007).

In the United States, between 2000 and 2017, the Legionnaires' disease rate increased 5.5-fold from 0.42 to 2.29 per 100,000 persons (Barskey et al., 2020). In 2017, among the Legionnaires' disease cases reported to the Centers for Disease Control and Prevention (CDC) National Notifiable Disease Surveillance System (NNDSS), the case fatality rate was 7% (Barskey et al., 2020). Most Legionnaires' disease cases are reported in the Summer to Fall months. Lower case numbers are reported in the Winter to Spring (Barskey et al., 2022). In 2014 the estimated cost in the United States for Legionnaires’ disease treatment was 402 million dollars (Collier et al., 2021).

In 1976, the United States' first recognized outbreak of Legionnaires' Disease occurred at Philadelphia's Bellevue-Stratford Grand Hotel (TIME, 1976). The bacteria, L. pneumophila had contaminated the water supply that the building used for its air conditioning cooling system, enabling exposure via aerosolization. Since the 1976 outbreak, many legionellosis cases and outbreaks have been caused by exposure to contaminated water aerosols in either a residence or office building setting (Garrison et al., 2016; Schumacher et al., 2020; Smith et al., 2019). In addition, many studies have detected L. pneumophila in hot water samples from residential and office buildings (Collins et al., 2017; Donohue et al., 2019a; Stout et al., 1992) (Buse et al., 2020; Donohue et al., 2019a, 2019b; Flannery et al., 2006; Moore et al., 2006; Pierre et al., 2019; Schwake et al., 2016).

In situations where there is a diagnosis of Legionnaires' disease, a residence or office building's hot water supply is often assumed to be the source of transmission (Garrison et al., 2016; Stout et al., 1992a; Wadowsky et al., 1982). The hot water environment provides a unique opportunity where a microbe can survive and multiply. The elevated temperature simultaneously increases a microbe's growth rate and decreases the amount of chemical disinfectant (e.g., chlorine or chloramine) in the water (Brazeau and Edwards, 2013; Cullom et al., 2020). The primary reason why a disinfectant is added to drinking water is to prevent microbial growth. Research by Jacangelo et al. (2002) and States et al. (1989); shows that the disinfectant type and its amount influence the likelihood of L. pneumophila's detection and growth. Since not all disinfectants have the same efficacy in preventing microbial growth, it is important to identify the factors (physical and chemical) that are associated with the risk of microbial contamination.

The objective of this study was to measure L. pneumophila contamination (detection frequency and concentration) in the hot water plumbing lines of three structure types: residences, apartments, and office buildings. A longitudinal sampling approach was utilized to determine if a structure had a sporadic (a single positive sample) or persistent (multiple positive samples) occurrence pattern. Additionally, a structure's age and area (sq. ft.) were assessed to determine if they were indicators of contamination. In addition to characterizing L. pneumophila incidence in the three structure types, the hot water's disinfectant residual was measured to identify the concentration at which efficacy was lost. Also, L. pneumophila environmental monthly detection rates by structure type were compared to CDC's legionellosis monthly case reporting data to determine if there are shared patterns. We hypothesize that a building's structural parameters could be risk factors for L. pneumophila contamination and the spread of legionellosis.

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