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The Impact Of Legionella

The Impact of Legionella

Legionnaire's disease is a bacterial pneumonia that has been very well established
in the public consciousness for more than 20 years. The United States is not
alone in suffering the effects of this disease; many countries around the world
have experienced similar problems.

The most infamous outbreak occurred in 1976 in a Philadelphia, Pennsylvania
hotel, where 32 American Legionnaires died from exposure to the bacteria. The
death toll for this incident was actually 34 people. One little-known fact is
that two of the people who died from exposure to Legionella pneumophilla never
even entered the hotel where the outbreak occurred. They were exposed by simply
walking past the hotel on one of the critical days of exposure.

Other high-profile cases include a 1985 outbreak in England resulting in 29
deaths. A 1996 outbreak in Spain resulted in 14 deaths, and a 1997 outbreak
on a cruise ship resulted in one death.

During the 20-year period that this bacterium has been recognized, scientists
have learned a lot about the causes and high-risk areas where it is found. High-risk
areas include those with water temperatures in the range of 77-108 degrees Fahrenheit
and a biofilm containing food for the bacterium. Technically, anyone can contract
the disease if the dose breathed is high enough.

Building mechanical systems, specifically cooling towers, were the first places
to be associated with the bacteria. The bacteria from the Philadelphia incident
was growing in the cooling tower water of a neighboring building. Mist from
that cooling tower was drawn in with the outside air for the hotel, allowing
the bacteria to be distributed by the hotel's HVAC systems.

Potable water can also contain Legionella bacteria. Often vacationers who contract
Legionnaires disease can trace their exposure back to contaminated shower water
in hotel rooms. Locally, workers at a Houston Federal building became exposed
while breathing vapors from the hot water used to wash their hands. Even those
using spas or hot tubs can be exposed to the presence of Legionella although
they are not considered as high a risk as the other areas mentioned.

What can you do to minimize the potential for bacterial growths? Some suggestions
include: 1) reviewing your high-risk water sources including cooling towers
and potable water to determine their condition 2) ensuring that any possible
sources receive regular and routine maintenance and that a buildup of bacteria
does not occur 3) developing a program to monitor Legionella in high-risk areas.
Such a program may include quarterly reviews and water sampling 4) implementing
and using a program designed to maintain disinfecting of cooling towers and
other water sources which could grow the bacteria 5) ensuring that potable water
temperatures exceed the ideal characteristics for growth of Legionella. This
means that water temperatures should be kept higher than 115 degrees Fahrenheit.

Finally, document every step that you make in ensuring a safe operating environment.
This is because even your best efforts are no guarantee that problems will not

Experience has shown us that documenting your due-diligence efforts serves
as a good line of defense when all else fails.

Next Week - Anything But IAQ Problems


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  [Posted by Building Air Quality on 12/2/2004] Reply to this message