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

Abstract

Aim: To observe how Legionella pneumophila, the causative agent for legionellosis, can transmit through the hot water plumbing of residences and office buildings.

Method and results: Using qPCR, L. pneumophila and L. pneumophila Serogroup (Sg)1 were measured in hot water samples collected from 100 structures, consisting of 70 residences and 30 office buildings. The hot water samples collected from office buildings had a higher L. pneumophila detection frequency of 53% (16/30) than residences, with a 10³ GU/L (median) concentration. An office building's age was not a statistically significant predictor of contamination, but its area (>100,000 sq. ft.) was, P = <0.001. Hot water samples collected at residences had a lower L. pneumophila detection frequency of 36% (25/70) than office buildings, with a 100 GU/L (median) concentration. A residence's age was a significant predictor of contamination, P = 0.009, but not its area. The water's secondary disinfectant type did not affect L. pneumophila detection frequency nor its concentration in residences, but the secondary disinfectant type did affect results in office buildings. Legionella pneumophila's highest detection frequencies were in samples collected in March-August for office buildings and in June-November for residences.

Conclusion: This study revealed that the built environment influences L. pneumophila transport and fate. Residential plumbing could be a potential "conduit" for L. pneumophila exposure from a source upstream of the hot water environment. Both old and newly built office buildings had an equal probability of L. pneumophila contamination. Legionella-related remediation efforts in office buildings (that contain commercial functions only) might not significantly improve a community's public health.

Keywords: Buildings; Households; Legionella pneumophila; Legionellosis; Premise plumbing; Residences; Water.

Fig. 1.

Legionella pneumophila (Lp) and L. pneumophila Sg1 GU/L concentration by residences (single-family homes + apartments) and office buildings and by sporadic/persistent detections.

Fig. 2.

Legionella pneumophila occurrence and persistence percentage by A) year built and by B) area (square footage) for each structure type.

Fig. 3.

Shows Legionella pneumophila concentration by total chlorine concentration for chlorine-and chloramine-treated water. A.) residences B.) office buildings. The table under the scatterplot is the number of samples in a specific total chlorine range (e.g., 0–0.2 mg Cl₂/L, 0.2–1.0 mg Cl₂/L, 1–2 mg Cl₂/L etc.). The black dotted line at 0.2 mg Cl₂/L is a reference point for the minimum residual amount at entry point into distribution. The vertical bar is the total chlorine median-mean range for a particular structure type (e.g., the pink bar is the total chlorine median-mean range detected in single-family homes with chlorinated water, the purple bar represents the single-family homes with chloraminated water, and the green bar represents apartments with chloraminated water).

Fig. 4.

Radial graphs show L. pneumophila and L. pneumophila Sg1 detection frequency by month for residences and office buildings. A) L. pneumophila-residential, B) L. pneumophila-office buildings, C.) L. pneumophila Sg1-residential, and D) L. pneumophila Sg1-office buildings.

Fig. 5.

Legionella pneumophila mean and median concentrations by month A) residences and B) office buildings.

Fig. 6.

Compares this study’s Legionella pneumophila monthly detection frequency (orange line) to the average percentage of legionellosis cases by month (purple bars). A) Legionella pneumophila residential monthly detection frequency compared to Hick et al. 2011 average percentage of legionellosis cases occurring annually by month and B.) compares L. pneumophila office buildings monthly detection frequency to CDC’s NORs 2009–2017 (month of first reported legionellosis case) average percentage of legionellosis cases by month. The density of the purple bar color indicates legionellosis case percentages: light purple is <7% of cases, median purple is 7–10% of cases, and dark purple is >10% of legionellosis cases.