Legionnaires' disease

Legionella bacteria under the microscope

Legionnaires' disease, also known as Legionellosis, is a rare form of pneumonia.

It takes its name from the first known outbreak which occurred in a hotel that was hosting a convention of the Pennsylvania Department of the American Legion in 1976.

The disease is fatal in approximately 5% to 15% of cases.

How is it contracted?

Legionnaires' disease is most often contracted by inhaling mist from water sources such as whirlpool baths, showers, and cooling towers which are contaminated with Legionella pnuemophila bacteria, or other bacteria in the family Legionellaceae.

If the bacteria reaches the lungs it can cause Legionnaires. The disease can only be contracted from a contaminated water system. It cannot be passed from one person to another.

The most common cause of the disease is contaminated air conditioning systems.

Mass outbreaks of the disease are rare.

What are the symptoms?

Legionnaires' has an incubation period of between two and 10 days.

Initial symptoms of are similar to those of flu - headache, musclepain, and a general feeling of being unwell.

These symptoms are followed by high fever and shaking chills. Nausea, vomiting, and diarrhoea may occur.

On the second or third day, dry coughing begins and chest pain might occur. There may also be difficulty breathing.

Mental changes, such as confusion, disorientation, hallucination and loss of memory, can occur to an extent that seems out of proportion to the seriousness of fever.

Some patients may develop pneumonia. This could affect both lungs and lead to hospitalisation if severe.

Who is most at risk?

Legionnaires' disease usually strikes middle-aged people. Those at risk include smokers and those with an existing health problem.

Many others may contract the bug and yet show no signs of infection. It is likely that many cases of Legionnaires' disease go undiagnosed.

People suffering from cancer or chronic kidney diseases are among those less able to fight infections.

Chronic diseases, such as diabetes and alcoholism, also seem to increase vulnerability to Legionnaires' disease.

Cigarette smokers are more likely to contract Legionnaires disease, perhaps because smokers are generally more likely than non-smokers to develop respiratory tract infections.

What is the treatment?

Legionnaires' is most often treated with the antibiotic drugs erthryomycin and rifampin. Recovery often takes several weeks.

How can Legionnaires' be prevented?

The likelihood of Legionella infection can be best reduced by good engineering practices in the operation and maintenance of air and water handling systems.

Cooling towers and evaporative condensers should be inspected and thoroughly cleaned at least once a year.

Corroded parts, such as drift eliminators, should be replaced. Algae and accumulated scale should be removed.

Cooling water should be treated constantly. Ideally, an automatic water treatment system should be used that continuously controls the quality of the circulating water.

Fresh air intakes should not be built close to cooling towers since contaminated water particles may enter the ventilation system.

This page contains basic information. If you are concerned about your health, you should consult a doctor