Encyclopedia of Health and Medicine

L–M
Legionnaires’ disease A serious and potentially
fatal form of PNEUMONIA first identified in 1976
when several hundred people attending a Legionnaires’
convention became ill, a number of whom
died as a result of the INFECTION. Scientists subsequently
isolated the causative bacterium Legionella
pneumophila. The BACTERIA infect about 18,000
people in the United States each year, about 4,000
of whom die from the disease or its complications.
A less severe form of the infection with the same
bacteria is Pontiac FEVER, which presents milder
forms of similar symptoms (though without subsequent
complications). Health experts refer to these
infections collectively as legionellosis. Heating and
cooling systems in buildings can harbor L. pneumophila,
which then spread the bacteria through
ventilation networks. Frequent and diligent cleaning
of these systems is the most effective means
for limiting outbreaks of infection.
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Symptoms and Diagnostic Path
Legionnaires’ disease begins as a typical viral
upper-respiratory infection with symptoms that
begin 3 to 10 days after exposure and include
fever, generalized aches and discomfort, loss of
APPETITE, HEADACHE, fatigue, and COUGH. Some people
also have gastrointestinal symptoms such as
diarrhea. Within a week the symptoms worsen to
include coughing up SPUTUM, chest tightness or
PAIN, and DYSPNEA (shortness of breath). Some people
also experience multiple neurologic symptoms,
including confusion and cognitive dysfunction.
A chest X-RAY shows signs of pneumonia, and
diagnostic blood tests often show indications of
infection in the body. The doctor may order specialized
tests to detect the presence of L. pneumophila in
the sputum or of L. pneumophila antigens in the
URINE. A key factor in suspecting Legionnaires’ disease
is knowing the possibility of exposure, either
because others have become ill or because the person
was at an event at a setting conducive to transmitting
Legionnaires’ disease, such as a large
convention. Other water sources as well as respiratory
equipment in hospitals harbor L. pneumophila,
which has become a common cause of communityacquired
pneumonia as well as of NOSOCOMIAL INFEC-
TIONS (hospital-acquired infections).
Treatment Options and Outlook
The primary treatment for Legionnaires’ disease is
hospitalization for intravenous therapy with the
ANTIBIOTIC MEDICATIONS of the macloide or fluoroquinoline
class (such as azithromycin or levofloxacin).
Illness in some people is mild enough
to allow outpatient treatment with oral antibiotics,
though others may require hospitalization. As
with any severe infection, multiple system failure
is a significant risk in people who already have
other major health conditions such as CARDIOVAS-
CULAR DISEASE (CVD), DIABETES, or pulmonary disorders.
Early diagnosis and treatment are critical; the
likelihood of death resulting from the infection
increases dramatically when people delay seeking
medical care or doctors are unaware of the possibility
of the diagnosis. Among people who are
otherwise healthy, have normal immune function,
and receive prompt treatment, more than 95 percent
recover. However, many people continue to
have some symptoms, such as fatigue, for several
months.
Risk Factors and Preventive Measures
Infection with L. penumophila can occur in several
venues. People who already have some form of
pulmonary compromise, such as ASTHMA or
CHRONIC OBSTRUCTIVE PULMONARY DISEASE (COPD),