L–M

Legionnaires’ disease A serious and potentially
fatal form of PNEUMONIA first identified in 1976
when several hundred people attending a Legion-
naires’ convention became ill, a number of whom
died as a result of the INFECTION. Scientists subse-
quently 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 subse-
quent complications). Health experts refer to these
infections collectively as legionellosis. Heating and
cooling systems in buildings can harbor L. pneu-
mophila, which then spread the bacteria through
ventilation networks. Frequent and diligent clean-
ing of these systems is the most effective means
for limiting outbreaks of infection.

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, andCOUGH. Some peo-
ple 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 peo-
ple also experience multiple neurologic symptoms,
including confusion and cognitive dysfunction.
A chest X-RAYshows signs of pneumonia, and
diagnostic blood tests often show indications of
infection in the body. The doctor may order special-
ized tests to detect the presence of L. pneumophilain
the sputum or of L. pneumophilaantigens in the
URINE. A key factor in suspecting Legionnaires’ dis-

ease is knowing the possibility of exposure, either

because others have become ill or because the per-

son was at an event at a setting conducive to trans-

mitting Legionnaires’ disease, such as a large

convention. Other water sources as well as respira-

tory equipment in hospitals harbor L. pneumophila,

which has become a common cause of community-

acquired 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 MEDICATIONSof the macloide or fluoro-

quinoline class (such as azithromycin or lev-

ofloxacin). 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 disor-

ders. 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 possi-

bility of the diagnosis. Among people who are

otherwise healthy, have normal immune function,

and receive prompt treatment, more than 95 per-

cent recover. However, many people continue to

have some symptoms, such as fatigue, for several

months.

Risk Factors and Preventive Measures

Infection with L. penumophilacan occur in several

venues. People who already have some form of

pulmonary compromise, such as ASTHMA or

CHRONIC OBSTRUCTIVE PULMONARY DISEASE (COPD),

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