pneumophila to enter a VBNC-like state (see Chapter 2, Allegra et al., 2008, 2011). Certain control strategies like heat treatment, chlorine-based disinfectants, and copper-silver ionization are known to trigger L. The majority of well-documented case studies base their evaluation on measurements of Legionella or Legionella pneumophila using culture-based methods, which cannot detect viable but nonculturable (VBNC-like) forms. Still, it is important to note that the type of Legionella detection method will also influence the perception of efficacy of various controls. This chapter provides information based on the targets that are described in the available literature. Notably, some treatments may shift the composition of types and virulence of Legionella, which is difficult to assess and not typically measured. The precise target for Legionella control can be quite complex in terms of species, serotypes, strains, and corresponding virulence factors. Although any of these water systems has the potential to grow and transmit Legionella, this discussion is limited to the premise plumbing of buildings, cooling towers, humidifiers, hot tubs, and corresponding water supplies, though some of the basic principles apply to other systems as well. In addition to drinking, potable water is used for other critical services in buildings, especially hot tubs, spas, and Jacuzzis (collectively referred to as hot tubs), cooling towers, humidifiers, decorative features such as fountains, medical equipment, dental units, and ice machines. NOTES: вњ” = a strategy has been successfully used in a particular system ? = a strategy could be partially used in a particular system, but there are noted limitations/considerations вњ– = a strategy is actually being worked against in a particular type of system blank boxes are where there is no indication that a strategy can be used in a particular system. TABLE 4-1 Overview of Legionella Control Strategies and Relevance of Their Application to Building and Water System Types Additional barriers, such as point-of-use size-exclusion filters, can also be considered for immunocompromised or other sensitive populations. Aerosols can also be diverted, as in the case of drift eliminators on cooling towers, to reduce potential for human exposure. Control of Legionella can be based on limiting not only its growth, but also the opportunities for humans to be exposed, for example by avoiding the formation of aerosols, particularly those of ideal size (less than 10 Вµm) for inhalation and deep deposition into the lungs.

Factors such as temperature, disinfectants, and distal devices can be more easily adjusted after building construction and during operation. For example, in a building, the pipe sizing, the materials and devices used, and the flow conditions are determined prior to the buildingвЂ™s construction and are more difficult to adjust once a building is operating. Many of these factors come into play during the initial building design and commissioning stages, while others can more readily be adjusted in existing buildings. The chapter also discusses emerging issues, such as potential conflicts among strategies for green building design, water and energy conservation, and more prospective Legionella control strategies.ДЄs detailed in the following sections, factors known to influence Legionella growth in water systems include temperature, disinfectant type and levels, hydraulic conditions (particularly avoiding stagnation), presence of nutrients, pipe materials, presence of distal devices, and extent of aerosol formation. Table 4-1 summarizes which specific controls are applicable to which building water systems and devices. The real-world application of these strategies for Legionella control in building water systems and devices is then described. A summary of the key strategies for controlling Legionella by affecting their growth and survival (or that of their free-living amoebae hosts) is presented first. Such controls should ideally begin as early as the design and commissioning phases and subsequently be applied routinely as preventative measures and, when necessary, for remedial purposes, i.e., in response to outbreak or flags raised by monitoring data.

This chapter focuses on strategies for Legionella control in building water systems. Strategies for Legionella Control and Their Application in Building Water Systems

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