Healthy Indoors Magazine - USA Edition

HI April 2014

Healthy Indoors Magazine

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Page 38 of 53

AirWays Environmental Services Legionella Continued from previous page Healthy Indoors 39 pends on who you ask." Starting at the source, municipal water systems have specific bacte- rial testing requirements, but Legionella is not among them. The non-regulatory "maximum contaminant level goal" (MCLG) established by the US EPA for Legionella is zero, but test- ing for Legionella by municipal water suppliers and achieving this goal is not required. Despite relying upon treatment strategies that "should" control Legionella, elevated levels of Legionella in the municipal water supply is a common find- ing. A recent study published in Environmental Science & Technology reported finding Legio- nella pneumophila serogroup 1 (LP1) in nearly half of the cold water tap samples taken from 68 different water supplies across the Unit- ed States.(1) While far from conclusive, this published study corroborates this author's ex- perience when we have sam- pled Legionella in the municipal water supplies of communities where at least one person had contracted LD. These unpub- lished findings attempted to examine munici- pal water supplies by sampling them at either multiple locations on one day or at a handful of locations over the course of many months. Elevated levels of Legionella in municipal wa- ter supplies were detected in 30% to 50% of samples. These concentrations of Legionella, including LP1, were typically low, and not be- lieved to be the source of infection. They were, however, the likely source of recurring inocula- tion in building water systems they served. Several factors probably account for these findings, and to most experienced investiga- tors this should be no surprise. It points to the unfortunate fact that building water systems are periodically being re-inoculated by the incom- ing municipal water supply. If proactive efforts are not taken to control Legionella, a building's plumbing system can become an amplification site. RECOMMENDED PREVENTION MEASURES Currently, there are a few guidelines and techni- cal documents that address recommendations for design, maintenance and operation of cool- ing towers and healthcare facility potable water systems. A number of voluntary guidelines have been published by non-govern- mental orga- nizations and industry as- sociations with the intent to provide building operators with general guid- ance on pre- vention. Due to their limited scopes and reliance upon experience and limited studies, none claim to be a panacea cure-all preven- tive for Legio- nella problems. In fact, most have practical limitations and only address Legionella prevention in broad brush strokes.(2,3,4) Reliance upon "evidence- based criteria" in current guidance documents is unclear. The consensus-based guidance they provide reflects experiences or small-scale laboratory testing that may not have been sub- jected to broader field studies of case control or cohort buildings. Controlling for confound- ers and validating results using statistical tests may be necessary to determine if they can be applied in a broader scale. The cost and effort for such studies are often beyond the budgets

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