Legionella bacteria under the microscope
Outbreaks tend to occur in healthy people staying in hotels or other buildings in which the cooling systems or showers have become contaminated by Legionella germs. They may also occur as single cases in which the source of the germs is uncertain.
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.
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.
The most serious effects are on the lungs, which may suffer damage that cannot be repaired, and this is the common cause of death. The mortality rate is about 4 per cent. Those especially at risk include older and unwell people, and heavy smokers and drinkers.
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.
Legionella germs tend to propagate in large, warm, moist areas such as air-conditioning towers. They are spread into the air in water droplets.
This is made by checking the levels in the blood of antibodies to the Legionella germ. A person with a recent infection will show a rapid rise in the antibody levels in quite a short period of time. There may be a four-fold rise in a few days.
The disease can be prevented by proper chlorination (treatment of water with chlorine) and sealing of water supplies.
Also 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.
Treatment includes antibiotics. Clarithromycin is currently the drug of choice. Other antibiotics may be used, such as erythromycin or rifampicin.