| dc.description.abstract | Legionella, particularly Legionella pneumophila, are opportunistic bacteria found in artificial and natural aquatic environments that may cause severe pneumonia, known as Legionnaires’ disease, and mild influenza-like Pontiac fever. Recent estimates attribute 1.5 to 2.0 deaths per million individuals to legionellosis in developed nations. This thesis aims to explore strategies for managing Legionella in drinking water systems, specifically, to minimize its introduction into the distribution network and control its proliferation within building plumbing systems.
We examined the impact of water intake depth on Legionella concentration because, in Norway, the placement of the water intake within the hypolimnion of the lake is regarded as a hygienic barrier against fecal-origin pathogens. However, its effectiveness against opportunistic pathogens such as Legionella remains unclear. Water samples from two lakes were collected at 10 m depth intervals near the drinking water intakes, and the presence of total bacteria, the genus Legionella, L. pneumophila and a common host for Legionella, Acanthamoeba spp., were quantified using quantitative real-time polymerase chain reaction (qPCR). L. pneumophila were also assessed by culture-based assay. The results did not reveal significant differences in total bacteria and Legionella spp. concentrations at the intake depths versus the lake surfaces for most of the sampling months. This finding suggests that the placement ofwater treatment plant intakes within the hypolimnion may not provide a sufficient barrier against Legionella.
There is a concern that Legionella in the natural environment (e.g., drinking water lakes) could pass through barriers in the drinking water treatment plant and enter the distribution network. Favorable conditions like warm temperatures and lack of residual disinfectant may aid the proliferation of Legionella in building plumbing systems. To control Legionella growth within building plumbing systems, the study investigated the effectiveness of flushing, which involves running water outlets to replace stagnant water with fresher water from water mains, a common recommendation by Legionella management guidelines. With buildings potentially receiving water with low or no residual disinfectant due to water age and different local regulations, the benefits of flushing have been poorly quantified. In a pilot-scale premise plumbing system, flushed and non-flushed shower outlets were evaluated during periods of both active and low water demand, in the presence and absence of chloramine, and at varying hot water set temperatures. The total bacteria, Legionella spp., L. pneumophila, and Vermamoeba vermiformis were quantified using qPCR, and flow cytometry (FCM) was used to quantify total cell count (TCC) and intact cell count (ICC).
Our results revealed that flushing effectively decreased the accumulated concentration of total bacteria in the stagnant water, regardless of the presence of disinfectant in the water supply. An important observation was the specific behavior of Legionella spp. Flushing led to an immediate decline in the concentration of Legionella in systems without disinfectant. However, this decrease was not observed when disinfectant was present. After resuming the period of active water demand, the flushed outlets showed marginally reduced quantities of Legionella compared to the non-flushed outlets. However, this difference was of minimal practical significance (<0.5 log10[copies/L]). Especially during low water demand periods, the concentrations were almost identical in the flushed and non-flushed outlets. Introducing chloramine with a contact time (CT) as brief as 10 mg min/L Cl2 led to a lag of 10 to 14 days in Legionella growth, a phenomenon not evident in the total bacterial population. Finally, our results highlighted thatFCM results (TCC and ICC) are reliable for representing total bacterial concentration measured as 16S rRNA genes, but not necessarily the Legionella concentration measured as ssrA genes within a plumbing system. These findings contribute to the body of knowledge on Legionella management in drinking water systems. | en_US |
