Legionnaires Disease & Domestic Hot Water Systems

Legionnaires Disease: New research from the US has identified home hot water pipes and domestic hot water systems as a common source of Legionnaires disease. Although more often associated with the air conditioning systems fitted to hospitals and large office buildings, Janet Stout, a microbiologist at the Veterans Administration Medical Center in Pittsburgh said, "The evidence suggests that the residential water system is an under appreciated source of Legionnaires disease."

Legionnaires' disease is a type of pneumonia and is named after an outbreak of severe pneumonia, which affected a meeting of the American Legion in 1976. The germ, which causes Legionnaires' disease, is a bacterium called Legionella pneumophila. People catch Legionnaires' disease by inhaling small droplets of water suspended in the air, which contain the Legionella bacterium.

This latest research, combined with earlier studies, now suggests the responsible bacteria often grow in the biological slime lining residential hot water pipes and domestic heating systems, and that home water may be responsible for up to 20% of cases. 

Stout estimates that between 2% and 5% of the 600,000 pneumonia cases requiring hospitalization in the United States each year are caused by the Legionella pneumophilia bacteria. Correct diagnosis is often missed because identification requires both a bacterial culture and a special urine test.

Stouts team investigated the sources of Legionnaires disease infections reported to health departments in Pennsylvania and Ohio. The families of 21 victims agreed to allow testing of their home water, and Legionella pneumophilia bacteria was found in 24% of those tested. Two of the patients studied died of their infections.

The bacterium, which causes Legionnaires' disease, is widespread in nature, flourishing at temperatures of between 90 and 105 Degrees F. It mainly lives in water, for example ponds, where it does not usually cause problems. Outbreaks normally occur from purpose-built water systems where temperatures are warm enough to encourage growth of the bacteria, e.g. in cooling towers, evaporative condensers, showers, whirlpool spas and from water used for domestic purposes.

People often keep the temperature in their hot water tanks set low to prevent scalding, but to kill the Legionnaires bacteria, Stout recommends temporarily turning up the temperature to above 140 Degrees F and running the hot water outlets for half an hour. Since the bacteria quickly return, this should be done regularly, especially if people prone to the infection are using the water. If the temperature is kept high, the bacteria return much more slowly or not at all.

"The overall perception we have that drinking water in the home is free of bacteria is a misconception," said Stout. "Although Legionnaires is a naturally occurring organism in water, people should be aware this is a potential source of disease."

The symptoms of legionnaires' disease are similar to the symptoms of the flu:

The illness is treated with an antibiotic called erythromycin or a similar antibiotic.

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