Legionella Control & Prevention

About Legionella

Legionellosis is a bacterial disease of environmental causes which generally appears in two differentiated clinical forms, that is, lung infection or Legionnaire’s disease, characterised by pneumonia and a high fever, and the non-pneumonic form, also known as Pontiac fever, which is an acute, nonfatal respiratory disease.

Infection with Legionella may be acquired within a community or within a hospital. In both cases, the contraction of the disease can be associated to different types of facilities, systems and buildings.

Legionella is an environmental bacterium, capable of surviving under a wide range of physico-chemical conditions, is apt to multiply between 20ºC and 45ºC, and is destroyed at 70ºC. The ideal temperature for it to grow is around 35-37ºC. Its natural ecological niche is surface waters, such as lakes, rivers and ponds, where it forms part of their bacterial flora. From natural reservoirs the bacteria causing Legionellosis can start colonising the water supply systems of towns and cities, and through the water supply network they slip in domestic water systems (hot and cold water), and other systems requiring water to operate, such as cooling towers. In some occasions poorly conceived systems with minimal or inappropriate maintenance favour stagnation of water, and hence the accumulation of substances on which the bacteria feed, such as mud, organic matter, corrosive matter, and amoebas, which together form a biofilm.

The presence of the said biofilm, in addition to a favourable temperature, explain the development of Legionella in infectious concentrations for human beings. If the system possesses an aerosol production mechanism, the bacteria can also spread through the air. This is so because the water drops containing the bacteria can stay suspended in the air and penetrate into the breathing system through inhalation.

The systems which more frequently are contaminated with Legionella and have been identified as sources of infection are domestic water supply systems (hot and cold water), and evaporative water cooling systems, such as cooling towers and evaporative condensers, both in health centres, and in hotels or other types of buildings.

  • Cooling towers and evaporative condensers.

  • Humidifying units.

  • Domestic hot water systems with a tank and a return circuit.

  • Heated water systems with constant agitation and recirculation (spas, swimming pools, therapeutic and hydromassage bathtubs.

  • Cold water systems for human consumption, such as tanks, reservoirs, or pipes.

  • Water spraying systems.

  • Vaporisers.

  • Firefighting water systems.

  • Sprinkler irrigation systems in urban areas.

  • Aparatos que puedan producir aerosoles.

  • Fuentes ornamentales.


ZECRON encompasses the requirements established in Royal Decree 865/2003 and Decree 352/2004, which lay down the health and hygiene criteria for the control and prevention of Legionellosis. As a result, we offer our clients the following services:

Water treatment in high risk systems.

Control plan:

  • General audit of the installation and issue of a report.
  • Control of the installation and parameters to follow.
  • Design and application of health and hygiene programmes.
  • Control of the critical points and parameters to follow.
  • Cleaning and cleansing of the systems.
  • Inspection of the system maintenance.
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