Legionnaires
INTRODUCTION
Legionnaires'
Disease,
infectious disease causing a severe form of pneumonia. It is produced by a
bacterium that colonizes warm, stagnant water and may be found in such places as
air cooling systems, humidifiers, and water taps. The bacterium was named
Legionella
pneumonia when, in 1976, 29 people died after suddenly becoming ill at an
American Legion convention in Philadelphia.
SYMPTOMS AND
DIAGNOSIS
Incubation of the
disease takes two to ten days, typically producing symptoms that may include the
rapid onset of fever, cough, chest or abdominal pain, headache or nausea,
vomiting, and mental disturbances. The fever may last about two weeks.
Complications can lead to kidney and lung failure.
Diagnosis may be
made by isolating the rod-shaped bacterium from blood and sputum samples and by
chest X-rays. Treatment with antibiotics such
as erythromycin, which may be
prescribed singly or in combination with others, has proved effective in
controlling the disease. Other antibiotics that may be used are rifampicin and
larithromycin.
People most at
risk are those with existing chronic lung disease, heavy smokers, the elderly,
and those whose immune system is suppressed, such as organ transplant
recipients. The disease can prove fatal, especially if respiratory failure
develops. There is no effective immunization against Legionnaires’ disease.
INCIDENCE
Although the form
of the disease known as Legionella pneumophila has been reported in North
and South America, Europe, Asia, Africa, and Australia, its precise incidence is
unknown. For example, in the United Kingdom the Public Health Laboratory Service
reported 160 cases including 27 deaths in England and Wales in 1994, resulting
in a rate of 3.1 cases per million of the population. Significantly, 56 per cent
of cases were associated with either domestic or foreign travel, which may be an
element in its spread. Related organisms that have been classified in the genus Legionella
are believed to have caused unidentified infections in the past. A linked strain
causes a condition known as Pontiac fever, which produces a much milder form of
pneumonia.
The bacterium is not easily transmitted by human contact. It may
infect people of all age groups, yet produce few or no symptoms in the young and
healthy. It is an organism that is found in both water and soil, but transmitted
to humans by air. Bacteria may be readily spread from their source, particularly
cooling towers that make thriving breeding habitats. Disease is caused because
the bacteria can easily be inhaled, indoors or out, in the vicinity of breeding
colonies. These may occur aboard cruise ships, near hotels and other buildings,
as well as in shower heads and whirlpool baths.
PREVENTION
Preventive
measures have proved effective. In buildings where a large number of people work
or congregate, water tanks should be kept either above or below the temperatures
at which Legionella rapidly colonize, that is, 20º to 50º C (68º to
112º F). Other measures also include disinfecting water supplies and the
drainage of water towers when they are out of service. The organism can be
destroyed by hyperchlorination or a method known as superheating. This involves
heating the water to 70º to 80º C (158º to 176º F) and flushing all outlets
for 30 minutes to kill the organism.