Legionella Risk Assessment

The Bacterium of Legionnaires’ disease or Legionella pneumophilia became known in 1976, when an epidemic broke out and 221 individuals (former legionnaires) were infected in a hotel in Philadelphia, USA; 34 of them died.

Legionnaires’ disease or Legionellosis is caused by the bacillus LEGIONELLA PNEUMOPHILA, the commonest and most dangerous species of LEGIONELLA family. This bacillus grows on surface waters, but can also be found in clean water. Legionella is transmitted mainly through the air, carried by very fine drops in aerosol form, which are formed through the operation of air-conditioning units, as well as showering or hand washing. The disease is not transmitted from person to person and it is treated with antibiotics.

Therefore, it is obvious that it concerns all businesses using water, either in closed systems, e.g. refrigeration & heating, or in open systems, e.g. swimming pools, jacuzzi, spas, etc., and predominantly:


  • Hotels
  • Food Industries
  • Office Buildings
  • Shopping Centres
  • Hospital Clinics
  • Wellness Centres – Swimming Pools – Swimming Baths


It should be underlined that under both European legislation (Directive 2000/54/ΕC), and National legislation (Presidential Decrees 186/95, 174/97, 15/99), Legionella spp. is included in agents that may infect individuals or even cause epidemic outbursts of Legionnaires’ Disease.

In social and working environments, ideal breeding grounds for the bacillus are the following:

  • Surface irrigation networks in areas with high temperature and exposed to sun radiation
  • Hot and cold water circuits for building use
  • Taps and Showers
  • Water-cooled industrial refrigeration/cooling systems based on water evaporation within cooling towers
  • Evaporative condensers
  • Humidifiers
  • Water fountains during hot summer days
  • Water-massage pools (spa), swimming-pools, etc.
  • Generally speaking, anywhere there is water that evaporates or being sprayed, where the temperature ranges from 25°C to 50°C and remains at this level over extended periods of time.

The aim
of this study is to assess the Legionellosis risk and, more specifically, to record the probability of Legionellosis and to establish a secure assessment system that will comprise:

  • Recording and assessing sources of Legionella infection within installations/premises
  • Recording points where water droplets are created and released
  • Recording factors impacting the survival and proliferation of the bacillus
  • Exposure to sensitive individuals.


During the risk assessment of Legionella growth, the entire production procedure is to be examined step-by-step, including permanent ancillary equipment for cooling – heating, so as to identify the critical points of network and water contamination. Assessment results can lead to businesses adopting the necessary procedures to be observed and documented by keeping relevant records.

In cases of equipment extension-modification, if significant changes in the procedures followed take place, or if alterations are made in water distribution systems, high-risk points and preventive measures implemented should be reviewed immediately.

Study deliverables

  • Specific preventive actions applying protocols that include, among other things, methods for disinfecting the systems of every installation
  • Maintenance plan for the plumbing system, disinfection schedule and all relevant interventions to be undertaken by technical experts
  • Schedule of necessary (minimal, as the case may be) water microbiological tests.

Legionella &&&&




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