Legionella and water sterilization

Legionella and water sterilization

11:46 13 April in News, Sterilization

Legionella Pneumophila, the cause of Legionnaires’ Disease, is a gram-negative, aerobio, usually hydrophilic bacterium, with sizes from 0.3 to 0.9 µm wide and from 1,5 a 5 µm length. Legionella includes 50 species and 70 serum groups; only 20 of these are able to give disease in humans.
In Italy, about 90% of cases of bacterial pneumonia are due to Legionella Pneumophilae and in particular to serum- group 1 and 6. Other species of clinical significance are: L. micdadei, L. longbeachae and L. dumoffii.


The most common type of Legionella transmission is inhalation of contaminated aerosols; the smaller the size of the droplets, the more dangerous they are, as with a diameter of less than 5 µm they easily reach the low airways.

The main infection sources for humans seem to be hot and cold water systems and air conditioning systems (air conditioning cooling towers, humidifiers, hydromassage, swimming pools, thermal baths etc.). Infection can also occur by inhaling dust particles generated from wet soil, water or contaminated ice intake, particularly in hospitalized patients, and for babies exposure at birth in the water. There’s no direct man-to-man transmission.


The probability of an infection depends on several factors:

  • presence of bacteria
  • dissemination effectiveness
  • how bacteria can multiply
  • source ability to form aerosols.


Knowledge of the factors that influence Legionella’s survival and growth in the environment is important, as it helps to identify riskiest areas in artificial water systems, indicating where and which control measures are most effective.

Legionella is an organism that spreads everywhere, especially in warm aquatic environments, between 25°C and 50°C, although it can live in temperature range from 6°C to 63°C. and pH between 2.7 and 8.1. In water systems, Legionella can be in free form, within ciliated and amaebe protozoa or anchored to biofilm, a film of microorganisms immersed in an organic matrix created in water networks, especially after reduced water flow or long periods of inactivity. Protozoa and biofilm are a source of nourishment and protection from unfavourable environmental conditions (temperatures, biocytes, etc.)



In 1901, Whipple noticed that adherence to surfaces increased the bacterial activity of water microorganisms; microorganisms, including L. pneumophila, form biofilms as a mechanism to resist adverse conditions, such as limited nutrients, extreme temperatures and biocides.

The biofilm consists of a film of microorganisms (bacteria, protozoa, viruses, mycetes, etc.) that adheres to irregularities of the inner walls of the pipelines, forming stratifications that have the effect of corroding the walls themselves, facilitating deposits and encrustations that protrude and occlude the pipes. The formation of stable communities is due to the activity of the “quorum sensing” (QS), a system of communication between bacteria, which allows microorganisms to counter and/or repair the damage caused by stress due to acid chemicals or temperature.



Biofilm prevention is an important measure of control against Legionella proliferation because, once established, it is difficult to remove.

A lot of factors increase the biofilm, including:

  • nutrients presence
  • corrosion
  • water temperature
  • low flow rate as in pipelines and storage tanks.


Measures to control the presence of microorganisms in water systems include:

  • selection of water system materials that do not serve as substrates
  • design of the hydraulic system to prevent water low flow
  • limiting the nutrient amount that facilitate the development of biofilms, especially organic ones
  • use of a disinfectant (e.g. a biocide)
  • use of chemical additives to control fouling, corrosion and microorganisms
  • water temperature control outside the ideal range for Legionella, keeping the cold water below 20/25°C and hot water above 45/50°C.



In addition to plant design and water temperature control, there are possibilities to intervene to prevent the spread of Legionella through the use of non-oxidant biocides, chlorine, monoclorammine, chlorine dioxide, hydrogen peroxide and silver ions, copper and silver, UV radiation, ultrafiltration at the building’s entry point, Point-of-use filters.

All of these methods, which can be adopted, individually or in combination, after the individual plant, the water system and the environment in which you operate, have advantages and disadvantages that will have to be taken into account when choosing the instrument to be used.


VitroSteril Water series offers Point-of-use filters because they are:

  • a valid physical barrier
  • easy to install
  • suitable for both hot and cold water systems
  • also indicated for use in systems that expose high-risk patients.