Nosocomial Tech Tip #5 - Nosocomial Legionella (Legionellosis)

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Nosocomial Legionella (Legionellosis)	 
	
Legionella bacteria are the causal agents of Legionnaires’ disease,
Pontiac fever, and related pulmonary illnesses. Although there are 39+
species, all capable of causing disease, over 85 percent of all recorded
legionellosis cases have been caused by a single species, L.
pneumophila. It has been estimated that up to five percent of the
pneumonia cases that occur in the United States are actually caused by
species of Legionella. Yet, perhaps as little as ten percent of these
are correctly diagnosed and reported to the Centers for Disease Control.
This high incidence of misdiagnosis has been attributed to failures of
physicians to order the analytical test and/or from false negatives that
are due to the insensitivity of the clinical test itself. 

Low concentrations of the bacteria occur ubiquitously in soils,
municipal water supplies, and particularly non-marine aqueous
environments. Complete eradication of Legionella in water supplies is
virtually impossible. Unfortunately, man-made water devices can create a
niche in which the water borne organisms grow and attain numbers that
would not normally be achieved in a natural environment. It is this
explosion in numbers that allows Legionella to become an opportunistic
pathogen. 

An estimated 8,000 - 18,000 cases occur each year in the United States,
23% of these are nosocomial. The medical significance of the Legionella
genus of bacteria was first recognized following a fatal outbreak of
pneumonia among members of an American Legion convention in 1976. Since
that time there have been many recorded outbreaks, as well as individual
cases of legionellosis. In many respects Legionnaires’ Disease is a
progeny of the technology age. Technology has facilitated many epidemics
by providing the means for efficient transmission of the bacteria and
has increased the number of susceptible hosts due to medical
advancements. 

Transmission of the bacteria is through man-made water devices that
typically have warm water, suitable pH, stagnation followed by
agitation, other living organisms present, and the presence of sediment.
These water devices can include cooling towers, potable water systems,
water systems in large buildings, whirlpool baths, respiratory care
equipment, hot tubs, fountains, electric water heaters, showers and
faucets. These sites are generally where "outbreaks" occur. Typically,
under these scenarios there are a number of victims and fatalities
occur. However, these "outbreaks" that garner so much media attention
are only a small percentage of the estimated 8,000 - 18,000 cases of
Legionnaires’ Disease that occur annually. 

Examination of water samples is the most efficient microbiological
method for identifying sources of Legionella bacteria. Of the available
methods for its detection in environmental samples, the culture method
remains the "gold standard". This method requires a ten (10) day
incubation period. A molecular technique, polymerase chain reaction, or
PCR for short, offers a very sensitive and specific method, and one that
only requires a few hours to complete. 

The number and types of sites that should be tested must be determined
on a case by case basis because of the diversity of plumbing and
mechanical systems in various buildings. Generally, any water source
that may be aerosolized should be considered a potential source for the
transmission of Legionella bacteria. Legionella can be found in
municipal water supplies at low levels and the organism tends to
colonize individual distribution systems and point of use devices.
Legionella are thermotolerant and are found frequently in hot water
systems. The bacteria are readily subject to desiccation and do not
survive outside of a water source. Therefore, condensate collection
devices from air conditioning equipment that frequently evaporate are
not a likely source. 

The investigator can collect two primary types of samples: water samples
and swabs of point of use devices or system surfaces. The amount of
water required by the laboratory for water samples depends upon the
detection limit required by the investigator. Generally 100 milliliters
of water is sufficient, unless a very low bacteria level is suspected
and circumstances dictate concentration of the sample to obtain a
detection limit of less than one organism per milliliter. If this is the
case, a one-liter sample should be collected. The investigator should
consult with the laboratory prior to collecting samples to determine
which sample volume is more suitable. Swabs permit the sampling of
biofilms, which frequently contain Legionella. These can be taken from
various points within the plumbing system, from surfaces of water
containing mechanical devices or from faucet aerators and showerheads.
All samples should be transported to the laboratory in insulated coolers
to protect against temperature extremes. Samples that cannot be
delivered to the laboratory within 24 hours of collection should be
refrigerated. 

Water sampling is the most effective means of determining the presence
of Legionella pneumophila. Air sampling is an insensitive method due to
the fact that the life span of the bacterium is typically short lived in
the aerosolized form. 

The PCR method provides an extremely powerful screening tool for very
rapidly detecting the bacterium in environmental samples, however it
does not distinguish between living and dead cells, but unless the
environment has been recently altered, such as with a biocide
application, moderate to high populations of Legionella detected by PCR
are usually indicative of an existing or potential future problem.
Therefore, the PCR method can rapidly identify potential sources,
facilitating disinfection processes and help to prevent further
exposures. As this method does not determine viability of the bacteria,
the PCR screen must be considered presumptive and requires confirmation
via conventional culture techniques. 

For more information on Legionella or sampling for Legionella, please
contact Aerotech Laboratories at 800.651.4802, or visit
www.aerotechlabs.com. 
	
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