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Frequently Asked Questions
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.
How
common is legionellosis in the United States?
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.
What
are the usual symptoms of legionellosis?
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.
How
is legionellosis diagnosed?
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.
Who
gets legionellosis?
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.
What
is the treatment for legionellosis?
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.
How
is legionellosis spread?
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.
Where
is the Legionella bacterium found?
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.
What
is being done to prevent legionellosis?
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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