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Legionella disease is a fatal and infectious disease caused by the gram negative bacteria. A majority of legionella disease cases are caused by certain strain of the bacteria known as Legionella Pneumophila, an aquatic microorganism that thrives in temperatures between 25-45°C.

There are two distinct forms of Legionella:

  • Legionnaires disease or legion fever – It is more severe. Victims suffering from this disease experience high fever and pneumonia.
  • Pontiac fever- Patients with this disease experience a milder form of respiratory illness without pneumonia.

The name of the disease stems from an outbreak of pneumonia that took place at a convention of the American Legion at a hotel in Philadelphia in July 1976. In January 1977, the bacterium that causes the disease was identified and named legionella. This strain was previously unknown. This bacterium affects people differently with some exhibiting mild or no illness.

Though outbreaks of the disease have created a big stir in the media, it usually occurs as isolated cases; the disease has not been associated with significant outbreaks. Although cases of the disease have been reported at various times of the year, most outbreaks occur during the months of summer and autumn. The disease mostly affects the middle aged or older people.

Symptoms of Legionella

  • Chills, fever and a cough. The cough may be dry or with a sputum. 
  • Some patients may have muscles aches, poor co-ordination, headaches, diarrhoea and vomiting
  • Confusion or impaired cognition
  • Low heart rates
  • Other symptoms may be diagnosed through laboratory tests and x-rays including:
  • Poor functioning of the renal glands and the liver
  • Pneumonia

Differentiating legionella disease from other forms of pneumonia is not easy and apart from radiological results, additional tests must be performed for proper diagnosis. People with Pontiac fever generally exhibit fever and muscle aches but never contract pneumonia. They also heal without medication in 2-5 days. The incubation period for legionella disease is about 2-10 days while that of Pontiac Fever is shorter from several hours to two days.

Transmission of Legionella

Infection happens when an individual inhales air borne particles with the legionella bacteria. The particles could come from any infected water source. Through mechanical action and evaporation, water breaks down into small droplets invisible to the naked eye and is carried into the air. The bacteria remain suspended in the water droplets until it is inhaled into the lungs. The rate of infection is higher in poorly ventilated rooms such as prison cells.

The sources of such contaminated water include cooling towers, humidifiers, spas, nebulizers, evaporative coolers, fountains, showers, windshields and ice making equipment among others.

Transmission may also be effected when a person inhales contaminated aerosols. This is the most common form of transmission especially from poorly disinfected hot tubs. Ponds, creeks and fountains are potential sources of legionella bacteria.

Prevention of Legionella

The bacteria responsible for legionella disease can travel airborne for at least 6 kilometres from its source. This greatly increases its chances of infection. Though a number of guidelines have been issued in a bid to reduce the rate of infections, some of the guidelines have been ignored. Despite the fact that the bacteria die in temperatures exceeding 60°C, various countries have limited the temperature for boiling water in health facilities to prevent scalding.

A study conducted by the UK Health Protection Agency found that a fifth of legionella disease cases in the UK are caused by infected water in windshield washer systems. These findings came after it was discovered that professional drivers have a higher likelihood of contracting the disease. No infections were found when the right washer fluid was used in the windshield washer system. An effective infection prevention strategy is to remove slime in water systems.

In 1986, the European Working Group for Legionella Infections (EWGLI) was established and assigned the responsibility of sharing information about the breeding habits of the bacterium and how the disease can be controlled. It has published several guidelines on prevention measures on limiting legionella bacteria colonies.

Almost all water sources contain Legionella bacteria. However, their presence in water should not be a cause for alarm. The bacteria thrives in warm water such as that in cooling towers, hot tubs, indoor water fountains and hot water systems. To prevent transmission, add an anti-bacterial agent in windshield washers, air conditioning systems and plumbing systems as well as all potential breeding grounds of the bacteria. Use sterile water especially when using respiratory care devices.

In the UK, the Health and Safety Executive (HSE) issues guidelines for Legionella disease control. These guidelines recommend weekly micro-biological monitoring of wet cooling systems. It also recommends frequent testing for Legionella Pneumophila during the commissioning of wet cooling systems.

Author: +Duncan Hollis