Legionella--an environmental issue and concern.

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William E. Pearson II, C.W.T., Association of Water Technologies

The discovery and identification of Legionella bacteria followed an outbreak of illness reported to the Pennsylvania health authority that resulted in 34 deaths among 231 afflicted people. The outbreak occurred in 1976 around a Philadelphia hotel that was host to an American Legion Convention--thus, the illness became known as Legionnaires' disease (LD).

Legionnaires' disease is a form of pneumonia, and the microorganism responsible for the disease is a naturally occurring water bacterium. Legionella is found in lakes, streams, rivers, groundwaters, and even some soils. It can escape water plant chlorination treatment and is thus found in domestic (potable) water plumbing and other water-use systems (e.g., commercial, industrial, process, and HVAC systems). In many of these systems, it finds conditions that favor a disease risk.

Outbreaks of legionellosis are often blamed on the air conditioning (cooling tower) systems of large buildings and commercial or industrial complexes. It is just as well established, however, that another common habitat for the disease-producing bacteria is in the hot-water and potable-plumbing systems of these same buildings. New research shows that residential hot-water pipes also can be a source of the bacteria (and the disease). A recent U.S. Environmental Agency (U.S. EPA)-sponsored study sampled for Legionella in the residential water systems of 21 Legionnaires' disease patients and linked five of the water systems to the disease bacteria.

Several conditions and factors must occur for Legionella to cause disease; sufficient quantity of the bacteria, a virulent form of the bacteria, or both must be made transmittable to a susceptible host. Transmission occurs when a host inhales tiny water droplets (mists or aerosols) containing Legionella or aspirates Legionellaladen water during the drinking (swallowing) process. These transmission routes provide entry of the infectious Legionella into the deeper parts of the lungs, where they take over and promote the pneumonia.

Legionella bacteria grow well and amplify in warm water environments and systems that provide favorable conditions for bacterial growth and the formation of biofilm. The optimum temperature range for growth is 90 to 105 degrees Fahrenheit. The subsequent use or release of water from systems harboring Legionella, (i.e., through faucets, shower sprays, humidifying devices, aerosolizing...

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