Legionnaire's Disease
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Legionellosis is an infection caused by the bacterium Legionella
pneumophila. The disease has two distinct forms:
- Legionnaires' disease, the more severe form of infection which includes
pneumonia, and
- Pontiac fever, a milder illness.
Legionnaires' disease acquired its name in 1976 when an outbreak of pneumonia
occurred among persons attending a convention of the American Legion in Philadelphia.
Later, the bacterium causing the illness was named Legionella.
An estimated 8,000 to 18,000 people get Legionnaires' disease in the United States
each year. Some people can be infected with the
Legionella bacterium and
have mild symptoms or no illness at all.
Outbreaks of Legionnaires' disease receive significant media attention. However,
this disease usually occurs as a single, isolated case not associated with any
recognized outbreak. When outbreaks do occur, they are are usually recognized
in the summer and early fall, but cases may occur year-round. About 5% to 30%
of people who have Legionnaires' disease die.
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Patients with Legionnaires' disease usually have fever, chills, and a cough,
which may be dry or may produce sputum. Some patients also have muscle aches,
headache, tiredness, loss of appetite, and, occasionally, diarrhea. Laboratory
tests may show that these patients' kidneys are not functioning properly. Chest
X-rays often show pneumonia. It is difficult to distinguish Legionnaires' disease
from other types of pneumonia by symptoms alone; other tests are required for
diagnosis.
Persons with Pontiac fever experience fever and muscle aches and do not have
pneumonia. They generally recover in 2 to 5 days without treatment.
The time between the patient's exposure to the bacterium and the onset of illness
for Legionnaires' disease is 2 to 10 days; for Pontiac fever, it is shorter,
generally a few hours to 2 days.
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The diagnosis of legionellosis requires special tests not routinely performed
on persons with fever or pneumonia. Therefore, a physician must consider the
possibility of legionellosis in order to obtain the right tests.
Several types of tests are available. The most useful tests detect the bacteria
in sputum, find
Legionella antigens in urine samples, or compare antibody
levels to
Legionella in two blood samples obtained 3 to 6 weeks apart.
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People of any age may get Legionnaires' diasease, but the illness most often
affects middle-aged and older persons, particularly those who smoke cigarettes
or have chronic lung disease. Also at increased risk are persons whose immune
system is suppressed by diseases such as cancer, kidney failure requiring dialysis,
diabetes, or AIDS. Those that take drugs that suppress the immune system are
also at higher risk.
Pontiac fever most commonly occurs in persons who are otherwise healthy.
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Erythromycin is the antibiotic currently recommended for treating persons with
Legionnaires' disease. In severe cases, a second drug, rifampin, may be used
in addition. Other drugs are available for patients unable to tolerate erythromycin.
Pontiac fever requires no specific treatment.
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Outbreaks of legionellosis have occurred after persons have breathed mists that
come from a water source (e.g., air conditioning cooling towers, whirlpool spas,
showers) contaminated with
Legionella bacteria. Persons may be exposed
to these mists in homes, workplaces, hospitals, or public places. Legionellosis
is not passed from person to person, and there is no evidence of persons becoming
infected from auto air conditioners or household window air-conditioning units.
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Legionella organisms can be found in many types of water systems. However,
the bacteria reproduce to high numbers in warm, stagnant water (90°-105° F),
such as that found in certain plumbing systems and hot water tanks, cooling
towers and evaporative condensers of large air-conditioning systems, and whirlpool
spas. Cases of legionellosis have been identified throughout the United States
and in several foreign countries. It is believed to occur worldwide.
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Improved design and maintenance of cooling towers and plumbing systems to limit
the growth and spread of
Legionella organisms are the foundations of
legionellosis prevention.
During outbreaks, CDC and health department investigators seek to identify the
source of disease transmission and recommend appropriate prevention and control
measures, such as decontamination of the water source. Current research will
likely identify additional prevention strategies.
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