Legionella, infection risk

Legionella is a bacterium that can cause serious respiratory diseases such as legionellosis. Legionella bacteria can proliferate in the water systems of buildings. The risk of infection by water is relatively high since legionella can survive in water at temperatures between 20°C and 50°C, ideal for bacterial growth. Water systems in buildings, such as cooling towers, air conditioners and domestic hot water distribution systems, can be real incubators for legionella.


How to avoid the proliferation of legionella in the water systems of buildings

Legionella is transmitted through the inhalation of small infected water droplets, such as those produced by showers, taps or air conditioning. The disease is not transmitted from person to person. To prevent legionellosis it is important to keep the water systems clean and well cared for. This includes regular cleaning of cooling towers and water tanks, maintaining water temperatures below 20 ºC or above 60 ºC, eliminating stagnant water in water systems, and controlling the concentration of chlorine in water.

Identification of risk areas and monitoring of water systems

Identification of risk areas and monitoring of water systems play a key role in preventing the proliferation of legionella in buildings.

First, it is important to carry out a detailed analysis of water systems to identify any critical points, such as heat storage tanks, water storage tanks and misting systems.

Once these critical points have been identified, installations should be regularly monitored for anomalies or changes in control parameters. In particular, the monitoring of water systems shall include the measurement of water temperature at different points in the plant, verification of the presence of chemicals such as chlorine and periodic review of plants to ensure that they comply with current regulations.

In addition, it is useful to take preventive measures to keep the plant in optimal hygienic conditions, such as periodic cleaning of heat storage tanks and water storage tanks.

Regular maintenance and cleaning of heating, ventilation and air conditioning systems

Regular maintenance and cleaning of heating, ventilation and air conditioning systems are essential to prevent the proliferation of legionella in buildings. Air conditioning is one of the most common places where legionella can proliferate.

Regular maintenance includes periodic checks to detect any leakage or failure, replacement of worn parts and cleaning of the entire air conditioning system. Cleaning the heating, ventilation and air conditioning systems requires the use of specific detergents to remove the deposits of limestone, dust, bacteria and other contaminants that can accumulate inside the plant.

There are several types of water treatment system that can be used to prevent the growth of legionella, including the use of biocides, the installation of filters, and water disinfection. One of the most common methods to prevent the growth of legionella is the use of biocides. These chemicals are added to water systems to kill any bacteria present and prevent their proliferation. Biocidal products may be based on chlorine, bromine, iodine or other chemical compounds.

Another effective method of preventing the growth of legionella is the installation of filters in water systems. Filters remove particles that can feed the bacteria and can significantly reduce the risk of legionella infection. There are several types of filters that can be used, including active carbon filters and ultraviolet filters.

Finally, water disinfection can also be carried out by physical methods such as ultraviolet irradiation. Maintenance must be carried out by qualified and specialized personnel, able to guarantee the effectiveness of cleaning operations and compliance with safety standards.

Water temperature control in water systems

Water temperature control is one of the main factors in preventing the proliferation of legionella in building water systems. Since the ideal temperature for the growth of the bacterium is between 20°C and 45°C keeping water outside this temperature range prevents the proliferation of legionella.

In Italy, potable water must be kept at a temperature between 10ºC and 25ºC at the point of distribution. However, in certain cases, such as in hospitals or nursing homes, hot water can be kept at a temperature above 60 ºC in order to disinfect plants and prevent the spread of bacteria. Thanks to the use of thermometers it is possible to constantly monitor the water temperature and adjust the hot water temperature to the points where the risk of contamination is greatest. To further reduce the risk of legionella proliferation, water cooling or heat treatment devices can be installed, which keep the water below the ideal temperature for the growth of the bacterium.

Biorisk assessment

Biorisk assessment: how to protect yourself

Three years after the outbreak of the Covid-19 pandemic and with the experience that follows, We are now all aware of how potentially dangerous exposure to biological risks is and how there are working environments where the biological risk is greater than others: laboratories and health facilities present exposure to biological risk quite different from that of an office. Through an in-depth assessment, the sources of biological risks can be identified, the risks involved can be assessed and effective strategies developed to prevent and control their spread.


Biological hazards are infectious agents or other substances derived from living organisms that can cause harm to humans and the environment. These dangers can be present in different forms, including bacteria, viruses, fungi and parasites. These dangers can be present in different forms, including bacteria, viruses, fungi and parasites. The risks associated with biological hazards depend on various factors, such as the type of hazard, the route of exposure and the susceptibility of the individual.

Deliberate use of biological agents and potential exposure risk

A biological agent is a microorganism, cell culture, endoparasite that can cause infections, allergies, intoxications. Microorganisms are a microbiological entity capable of reproducing or transferring genetic material. Cell culture is the result of in vitro growth of cells derived from multicellular organisms.

According to the Legislative Decree 81/08 art. 271 there is deliberate use of biological agents when they are deliberately introduced into the working cycle to undergo various treatments and exploit their biological properties. As an example some activities with deliberate use of biological agents are the laboratories of universities and research centers, health, zooctenia and veterinary, pharmaceutical companies. If, on the other hand, the presence of the biological agent is not intentional because it is not a specific object of the activity itself, then we talk about activities that involve a potential risk of exposure.

Transmissibility and vehicles of infection

Biological agents may be transmitted for respiratory (aerodispersi microbes), oral, cutaneous, parenteral (introduction of substances into deep tissues by means of scalpels, needles, scissors and other sharp instruments), via passive vector arthropods (organisms that passively carry pathogenic microorganisms) or active type (for example mosquitoes, lice, fleas).

The vehicles of infection are air (closed and poorly ventilated working environments), contaminated water, soil, hands, blood and blood products.

Types of biorisk assessment

The biological risk is the probability that an individual comes into contact with a pathogenic organism, becomes infected and contracts a disease. There are basically two levels of assessment: assessment of the intrinsic dangerousness of the biological agent and assessment of the risk of infection of exposed workers. In other words, it is both qualitative and quantitative.

Potential biological hazards in a workplace or environment are identified through observations, interviews and literature analysis. The objective is to identify sources of biological risk, routes of exposure and probability of exposure. The level of exposure to biological hazards shall then be quantified. This assessment is based on the measurement of the biohazard concentration and the duration of exposure. The objective is to determine the level of risk posed by biological risk and to develop effective control measures.

Stages of the biorisk assessment

The biorisk assessment process shall include several steps, including the identification and assessment of biological risks, the development of effective control measures and periodic biorisk assessments.

The first phase of the biorisk assessment involves identifying potential sources of biorisk in the workplace or the environment. This assessment shall include an assessment of the likelihood of exposure, the routes of exposure and the consequences of exposure. The assessment shall also include the identification of the subjects most at risk of exposure, such as health professionals and laboratory technicians. Once the risks have been identified, the next step is to assess their severity and probability.

The second phase of the biorisk assessment involves the development of effective control measures to prevent or minimise exposure to biological hazards. Control measures may include administrative controls, such as policies and procedures, and technical controls, such as ventilation systems and personal protective equipment. The effectiveness of control measures should be regularly assessed to ensure that they are still effective in preventing exposure to biological risks.

There is also a third stage, which applies to all risk assessments, with periodic assessments to ensure that control measures remain effective and that new risks are identified and addressed. Regular evaluations should be conducted regularly and the results used to update the risk assessment and control measures. In addition, new employees or changes in working practices must trigger a new assessment to ensure that risks are still properly controlled.

PPE for biological risk

The objectives consist in the reduction of the dangerousness and the exposure also through the use of suitable DPI which:

  • gloves: must be CE marked as PPE and meet the requirements of EN 374 for protection against micro-organisms;
  • disposable masks, masks with filter, self contained breathing apparatus;
  • tyvec suits;
  • goggles and visors: with CE marking as PPE according to the requirements of UNI EN 166.

Biorisk assessment tools and techniques

Biorisk assessment requires expertise in various disciplines, including microbiology, toxicology, and epidemiology. There are several tools and techniques used in biorisk assessment, including:

  • risk assessment checklists,
  • exposure monitoring,
  • air sampling and analysis,
  • sampling and analysis of areas,
  • health surveillance.

The choice of tools and techniques depends on the type of hazard and the environment in which it is present. Air sampling may be more appropriate for the biological risks carried by air, while surface sampling may be more useful for the biological risks present on surfaces.