Definition:
Legionnaires' disease is an infectious disease caused by bacteria belonging to the genus Legionella. Over 90% of
legionellosis cases are caused by Legionella pneumophila, a ubiquitous aquatic organism that thrives in warm
environments (25 to 45 °C with an optimum around 35 °C).
Diagnosis:
The most useful diagnostic 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. The urine antigen test
is simple, fast, and very reliable. However, the urine antigen test will not identify the specific sub typing so
it cannot be used to match the patient with the environmental source of infection.
Treatment:
Current treatments of choice are the respiratory tract quinolones (levofloxacin, moxifloxacin, gemifloxacin) or
newer macrolides (azithromycin, clarithromycin, roxithromycin). The antibiotics used frequently have been
levofloxacin and azithromycin. Macrolides are used in all ages while tetracyclines are prescribed for children
above the age of 12 and quinolones above the age of 18.
Symptoms and Signs:
Patients with Legionnaires' disease commonly have fever, chills, and a cough, which may be dry or may produce
sputum. Most of the patients also have muscle aches, headache, tiredness, loss of appetite, loss of coordination
(ataxia), and occasionally diarrhea and vomiting. Laboratory tests can show that patients' renal functions, liver
functions and electrolytes are deranged, including hyponatremia.
Causes:
This disease usually occurs as a single, isolated case not associated with any recognized outbreak. When an
outbreak happens, they are usually recognized in the summer and early autumn, though cases may occur at any time
of year.
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