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Logan Moxley
BIO 112
Mrs. Caplan
Legionnaire’s Disease
Legionnaire’s disease was first identified and described in January 1977. Even today it is
often regarded as an unusual or exotic disease, when in fact it is a very common form of
community and nosocomial acquired pneumonia (Lane, 2004).
By the fall of 1976 the Swine Flu had been excluded as the cause of the Philadelphia
outbreak and several other theories were beginning to emerge, including conspiracies against
American veterans. The Centers for Disease Control and Prevention (CDC) interviewed over
4,000 Legionnaires and their families, and collected hundreds of environmental samples from the
hotel and its surroundings. Then January 1977, a CDC team isolated the bacterium that was
isolated responsible for the outbreak. Further investigation into the hotel’s environmental
systems revealed the bacterium thrived in the air-conditioning unit. The organism was named
Legionella pneumophila: Legionella for the persons from whom they isolated the bacterium and
pneumophila because the organism “likes the lungs” (Lane, 2004).
The elusive and previously unrecognized bacterium acts as an intracellular pathogen that
invades and replicates within free-living protozoa and mammalian cells. The bacterium is found
commonly in many fresh water environments including rivers, lakes, ponds, potable water
systems, soil and aerosolizing devices, such as cooling towers, showers, whirlpools, and spas
Microbiologists have identified at least 28 different types of the bacterium, but Legionella
pneumophila stereotype 1 is responsible for most cases in the United States (Lane, 2004).
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In the United States, Legionnaire’s Disease is consistently ranked among the top cases of
community acquired pneumonia, accounting for an estimated 2% to 15% of cases annually. It is
estimated that over 25,000 cases of community-acquired Legionnaire’s Disease occur in the
United States and cause more than 4,000 deaths every year. More than 95% of actual cases may
go undetected. Because outbreaks are widely publicized, the disease enjoys a false, but ongoing
reputation as an exotic plague (Lane, 2004).
The diagnosis for Legionnaire’s disease at this time is recognized by four laboratory
methods. The four methods are urine antigen test, culture of the organism, direct fluorescent
antibody staining, and serology. The urine antigen test provides rapid and accurate diagnosis of
disease caused by L. pneumophila. It has been reported to be one of the most powerful methods
used. However 80% to 90% of the clinically diagnosed cases are caused by serogroup 1 and the
urine test is being used increasingly (Lane, 2004).
It is estimated that in the United States there are between 10,000 and 50,000 cases each
year. For someone to get Legionnaire’s disease they must be exposed to water contaminated
with Legionella bacteria. This exposure may happen by inhaling or drinking water contaminated
with Legionella bacteria. Legionnaire’s disease is not contagious and cannot be transmitted from
one person to another. Legionnaire’s disease is not easy to diagnose the pneumonia caused by
Legionella is not easy to distinguish from other forms of pneumonia. A number of diagnostic
test allow a physician to identify the disease (Lane, 2004).
Legionnaire’s disease is a disease that can be prevented. Avoiding water conditions that
allow the organism to grow high levels is the best means of prevention. Specific preventive
steps include: Regularly maintain and clean cooling towers, evaporate condensers to prevent
growth of Legionella. Maintain domestic water heaters at 140 F. Avoid conditions that allow
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water to stagnate. Large water-storage tanks exposed to sunlight can produce warm conditions
favorable to high levels of Legionella. Frequent flushing of unused water lines will help
alleviate stagnation (Lane, 2004).
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