by Alex Musk


  • What is legionellosis?
  • Where is Legionella and in what conditions does it survive?
  • How do you get legionellosis?
  • Legionellosis: what are the factors that predispose to the disease?
  • How does a legionella infection manifest itself?
  • The Legionnaire’s Malattia 
  • Pontiac Fever
  • How to prevent the spread of legionella?
  • Covid-19: how to prevent legionella contamination
  • Normal control regime
  • Extraordinary control regime

Legionnaires’ disease is a disorder caused by legionella, one of the most frequent pathogens that are transmitted through the water. This bacterium can give rise to an acute form of pneumonia, so it is essential to implement a series of actions to prevent its spread, even more so in light of the Covid-19 pandemic, a situation that has led to the Istituto Superiore di Sanità to publish a specific guide to prevent the risk of legionella in the face of the pandemic. So let’s find out what legionellosis is, how it manifests itself and why, due to the Coronavirus, it is necessary to pay further attention.WHAT IS LEGIONELLOSIS?



When we talk about legionella Legionella pneumophila ) we refer to a bacterium responsible for a disease called legionellosis, which mainly affects the respiratory system, also causing acute forms of pneumonia. The name derives from the epidemic that, in 1976, struck the participants in the gathering of veterans of the American Legion who were staying at the Bellevue Stratford Hotel in Philadelphia, a circumstance in which 221 people became ill and 34 died of this hitherto unknown disease. The bacterium, on that occasion, was isolated in the air conditioning system of the hotel. 

Although several species of legionella have been identified (the genus legionella includes more than 60 different species, divided into about 70 serogroups), legionellosis is caused, in most cases, by legionella pneumophila. 




Where is this bacterium found and what are the conditions that favor its spread? 

Let’s start by saying that legionella prefers humid and warm environments. It can be found in muds and natural aquatic environments such as rivers, lakes, spring waters, including thermal ones. From these places it reaches artificial environments, such as city pipes and building water systems (swimming pools, tanks, pipes, fountains, etc.), which can therefore become a vehicle for the spread of the bacterium in the population, creating a potential medicare risk. 

There are some conditions that, within the water systems, favor the growth of legionella to a level that can cause infections: a water temperature between 20 and 50 ° C, the presence of stagnant water, and the development of elements such as biofilms, encrustations, algae, etc. in pipes or tanks.


Legionellosis is contracted by air, breathing aerosols containing legionella. While cases of infection through wounds have been reported in the literature, the passage of the bacterium from person to person has not been demonstrated.

The droplets we are talking about can be formed in different ways, for example by spraying water, by impacting it on a hard surface, or by bubbling air into the water. In any case, the smaller the drops are, the more easily they will be able to reach the lower respiratory tract. 

Epidemic outbreaks, as stated on the website of the Ministry of Health, have been found in collective environments such as hotels, hospitals, cruise ships, commercial exhibitions: except for those that occur in hospitals, which do not have a particular seasonality, contracted infections in collective environments they occur mainly in the summer-autumn months. 


Several risk factors favor the development of this pathology. Among these, we point out the advanced age and belonging to the male sex, in addition to cigarette smokingalcohol abuse, the presence of chronic diseases, and being immunosuppressed. Furthermore, individual susceptibility, the quantity of bacterium present in the contagion vector, and the exposure time, as well as its infectious charge, also affect. Although it is a bacterium that can be found in different places, however, the disease in humans remains rare: even during epidemic outbreaks, the infection rates are less than 5%.




Legionella can cause two different clinical conditions, Legionnaires’ Disease or Pontiac Fever: let’s see how they manifest themselves and what their consequences are.


It is the most severe and usually involves an acute form of pneumonia. With an incubation period that can range from 2 to 10 days, this pathology has characteristics similar to other forms of pneumonia and, in the less severe manifestations, fever, malaise, and mild non-productive cough can be found. Severe cases, on the other hand, may present with symptoms such as fever, difficulty in breathing (dyspnea), chest pain, cyanosis, and a productive cough, for example. 

It is also possible that extrapulmonary symptoms of gastrointestinal, cardiac, and neurological nature may occur, and that the pathology may undergo complications such as lung abscess and respiratory failure, for example.


It has an incubation period of 24-48 hours, it represents a milder form of the disease. It does not affect the lungs, in fact, and manifests itself with the typical symptoms of the flu (general malaise, muscle pain, headache, fever, etc.), moreover, it tends to resolve more quickly, within 2-5 days. 

As for the mortality rate associated with Legionella infection, as explained by the Istituto Superiore di Sanità, this can vary from 40-80%, in the case of untreated immunosuppressed patients, to 5-30% if the disease is treated. appropriately. Overall, mortality fluctuates between 5% and 10%.


What are the behaviors that make it possible to prevent severe Legionella contamination? Given the conditions that favor the development of this bacterium, among the main actions to be adopted, we find the correct design and construction of water networks and systems at risk, i.e. those that involve heating and/or nebulization of water (hydro- sanitary ware, swimming pools, whirlpools, air conditioning systems with water humidification, cooling systems with evaporative towers or evaporative condensers, etc.), to which is added the implementation of adequate preventive measures on the systems ( maintenance and, when necessary, disinfection). Furthermore, it is advisable to opt for instant hot water production systems, rather than systems that make use of storage tanks. 




After having discovered what legionellosis is, let’s see what the relationship is between legionella and Covid-19. As we have anticipated, the Istituto Superiore di Sanità has recently published a document for the prevention, control, and management of the legionella risk in the light of the CoronavirusThe Report is addressed to the managers of tourist accommodation facilities and to other buildings for civil and industrial use (for example workplaces, schools, catering activities) that were not used during the pandemic, and to the authorities responsible for the protection of health.

Why does the legionella problem arise concerning the Covid-19 emergency? The reason is this: the lockdown period has led to the closure of buildings or parts of them, or to limited use of certain structures, a factor that has determined the occasional use of some systems and, consequently, the prolonged stagnation of water within the internal distribution networks. This condition can represent a risk for the spread of legionella, so adequate action must be taken to ensure the safety of people when these buildings are reopened.

The indications, which can be read in full in the Report published by the ISS, are in addition to what is reported in the national guidelines for the prevention and control of legionellosis and following the Legislative Decree 81/2008 and the Ministerial Decree of 14 June 2017 concerning water safety plans. 

The guide contains both the instructions to be implemented in the event of a normal control regime and those aimed at an extraordinary control regime, for buildings that have been closed for more than a month. Let’s see them better.


This regime is envisaged for structures that have been closed for less than a month or where periodic flushing of the water from the taps and showers has been ensured. In this case, it is required that:

  • the risk assessment is reviewed and updated based on the current use of the water system, as well as that of other appliances and systems that have a reduced use or have been subjected to a state of shutdown;
  • being documented how employees, visitors, and other persons who will attend the building will be protected from the risk of infection at the time of re-opening;
  • if necessary, the manager uses an expert advisor and a safety officer.


On the other hand, when planning the reopening of a building that has been closed for more than a month, we need to act differently. The Istituto Superiore di Sanità, in this case, indicates precise measurements. Among the main ones:

  • check that there is a correct circulation of hot water in all parts of the water system, that the water temperature in the boiler or the storage tank is not lower than 60 ° C, and that that is measured in correspondence with the return from the recirculation rings is not lower than 50 ° C;
  • check that, from each outlet terminal, the hot water reaches a temperature of not less than 50 ° C within one minute of opening the terminal and that the cold water temperature does not exceed 20 ° C after flushing for 1 minute ;
  • clean, descale or replace, if necessary, the hot and cold water terminals, also abundantly flush and periodically disinfect the toilet cisterns, urinals, by-passes, and all other points on the network with chlorine;
  • check that the drinking water storage tanks contain free residual chlorine: the recommended value is 0.2 mg / l;
  • keep temperatures and biocide levels under control for at least 48 hours, making adjustments if necessary, then take water samples in search of legionella from the sentinel terminals; if the samples are negative it means that the hot and cold water terminals are under control and the facility can be reopened.

In addition to these measures, the report also recommends:

  • check the conditions of other plant systems that could lead to a risk of legionella contamination, for example, evaporative cooling towers, whirlpools in hotel rooms, air handling units; 
  • for systems subjected to a standstill, intervene with a complete cleaning of the equipment and associated water networks ;
  • as regards the evaporative towers, always carry out cleaning, disinfection, and drainage interventions;
  • carry out the operations described so far even if the system has previously been drained, as residues and condensation could favor the development of legionella (small devices that can be physically dried are excluded from this step).

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