Legionella is the bacteria responsible for Legionnaire’s Disease, an acute bacterial infection of the lower respiratory tract. This bacterium was first identified in 1977 by the Centres for Disease Control as the cause of an outbreak of pneumonia that caused 34 deaths at a 1976 American Legion Convention in Philadelphia.
Pontiac Fever is a less severe, non-pneumonia, flu-like disease that is associated with and likely caused by Legionella bacteria. Legionella is a fairly common water bacteria and has been found to exist widely in many surface water sources such as; lakes, rivers, streams and ponds. It can also be found in ground water sources and some soils.
At the levels found in these naturally occurring sources it typically does not pose a threat to public health.
When the bacterium enters a domestic water system it can find an ideal host environment of warm water temperatures 40-46°C, stagnant water areas (storage tanks and dead-end piping legs) and ample food sources (sediment, scale, deposits and biofilm).
Under these conditions Legionella can rapidly colonize, forming higher concentrations that can pose the public health threat of Legionnaire’s Disease.
There are many methods of controlling colonization of Legionella bacteria. However, a widely accepted and preferred method is to maintain the hot water system storage temperature continually at or above 60°C. Unfortunately, the elevated temperature necessary to minimize the growth of and kill Legionella bacteria has the potential to cause serious scalding injuries.
Thermostatic Mixing Valves maintain and limit the mixed hot water to a desirable, selectable temperature allowing for the storage of domestic hot water at the higher temperatures necessary to reduce the risk of Legionella growth in the system.