Legionnaires' Disease

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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.

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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.

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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. In the United Kingdom there are about 200 cases a year, of which up to 40 are fatal. Approximately 56 per cent of cases are associated with either domestic or foreign travel, which may be an element in its spread. It is estimated that around 10,000 people develop Legionnaires' disease each year in the United States, and studies have shown that about 5 to 15 per cent of known cases have been fatal. 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.

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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.