Legionella: how to prevent it

To prevent legionellosis, periodic maintenance is necessary to avoid the risk of water contamination.

Legionella, also called legionellosis, owes its name to an epidemic that in 1976 struck a group of American veterans belonging to the American Legion. The investigations following the 34 deaths that occurred on that occasion led to the isolation of a bacterium, called Legionella pneumophila, in the air conditioning system of the hotel where the veterans resided.

Since then, the microorganism has been studied and kept under control, mainly thanks to punctual and constant interventions to prevent the risks associated with legionellosis.

The prevention of this disease is a complex and articulated matter that requires not only the intervention of institutions and the health authority on the territory, but also the surveillance and attention of the individual, for whom it is essential to know the risks related to daily life.

Legionella: what it is and how the infection manifests itself

Bacteria belonging to the genus Legionella are quite resistant: they survive at a temperature between 5 and 55 ° C. In nature, they can proliferate in various water sources, from springs (including thermal springs) to rivers, lakes and stagnant waters, and then eventually reach aqueducts, pipes, fountains, swimming pools, all environments potentially at risk for human health.

Legionella infection is contracted through the inhalation of contaminated water in the form of an aerosol, through which the bacterium comes into contact with the lungs triggering the actual infection.

Legionella manifests itself in two forms: the milder one, known as Pontiac fever (from the name of the US locality, in the state of Michigan, where the first epidemic of this febrile form was recorded, which resolves spontaneously in a few days), and the more serious one, which is instead much more subtle as it has symptoms partly similar to those of the most common respiratory diseases. Let’s see how they differ:

Incubation period Symptoms
Pontiac fever It generally occurs within the first 48 hours of exposure Flu-like symptoms, such as nausea, fever, coughheadache
Legionellosis 5-6 days It is characterized, like pneumonia, mainly by fever, headache, cough, diarrhoea and muscle pain, but may also involve nervous system and kidneys

It is still difficult to establish the exact incidence of the disease, which is often not diagnosed. According to what was announced by the Higher Institute of Health, the data relating to the cases diagnosed and notified to the National Legionellosis Registry in 2016 indicate an incidence of 28.2 cases per million inhabitants in Italy.

In particular, elderly subjects, smokers and immunosuppressed patients or patients suffering from chronic or degenerative diseases are more at risk of contracting the infection; In these cases, the mortality rate may be significantly higher.

The diagnosis can only be ascertained by a specific laboratory test that certifies the presence of the bacterium in culture or through the analysis of the antigen in the urine. In case of certain diagnosis, a therapy based on specific antibiotics is appropriate, the prescription of which is up to the treating doctors.

Legionella: how it spreads

A positive fact, in the context of a subtle pathology like this, is represented by the fact that the infection is not transmissible between human beings; since 1976 no case of contagion from one patient to another has been documented.

However, attention should be paid to how and where the disease spreads to reduce the chances of transmission. By the very nature of the bacterium, which tends to proliferate especially in water systems, the environments in which there is a risk of spreading the bacterium can be those in which stagnant water accumulates or those at home, work, public buildings or any other place where water is supplied even partially nebulized (taps and shower diffusers, but also systems such as cooling towers, condensers, vaporizers and air recirculation systems).

As far as epidemiological aspects are concerned, outbreaks of legionellosis can manifest themselves in various ways: they can be due to a single source or to several independent sources in geographical areas particularly at risk, or they can be a sporadic manifestation. In any case, the infection is more likely to occur in community settings such as hospitals and hotels. Outside the hospital environment, legionella pneumonia occurs more frequently in the summer and autumn months.

Legionella prevention: who takes care of it, how it is implemented

With the above in mind, national and European institutions have prepared guidelines for the prevention and control of legionellosis, aimed above all at protecting “sensitive targets” such as hospitals, nursing homes, hotels, restaurants and other accommodation facilities.

The purpose of these guidelines is to reduce the likelihood of legionella contamination in the water systems and air conditioning systems of these facilities. The interventions envisaged in this sense are to be considered both reclamation and periodic maintenance of the plants themselves.

Periodic maintenance interventions are particularly important for accommodation facilities with seasonal characteristics. It is essential especially for these activities to proceed with the cleaning and sanitization of showers, taps and tanks: these are effective interventions both in terms of prevention and in the case of remediation to be carried out with a confirmed contamination in progress, to limit and limit its spread as much as possible, guaranteeing the safety of the people potentially involved.

It goes without saying that this type of intervention cannot be separated from an accurate risk analysis activity that takes into account the specificities of the structure involved.

The remediation activity can be carried out using chemical treatments (for example hyperchlorination) or by mechanical methods such as thermal shock, which consists in bringing the water of the affected plant to a temperature of 70-80 ° C to cause the immediate death of the bacterium.

It should be remembered, however, that every method has limits: the introduction of chemical agents involves a thorough washing of the system, the thermal shock kills the bacterium but does not affect the biofilm, aggregate of sugars and proteins produced by the bacteria themselves, in which they can continue to proliferate “undisturbed”. For this reason, each option must be carefully evaluated by the competent health authorities.

The provisions of the institutional guidelines also apply in part to more restricted and personal environments such as professional offices and private apartments. In these cases it is to be considered essential a periodic cleaning and disinfection of air conditioners, taps, shower diffusers, worn gaskets and any tanks. Particular attention is paid, in this sense, to dental practices, in which it is common to use instruments that generate aerosols, to which must be added the tendency of the bacterium to develop the so-called biofilm and adhere to surfaces: the risk of exposure is therefore high for both patients and operators and surveillance measures are in this case particularly stringent.

At industrial level and in public facilities, prevention is a strictly regulated matter and periodic maintenance and monitoring interventions are planned, as well as specific disinfection treatments in case of confirmed contamination.

In our homes, however, the most sensitive points are mainly air conditioners and taps: for the former, it is good to intervene regularly through a thorough cleaning of the filters. For taps and diffusers of the showers, care must instead be taken to periodically descale the mixer terminals, replacing gaskets and worn parts. If the water system remains inactive for a long time, perhaps for a holiday or an extended stay elsewhere, it is also a good idea to let the water drain from all the taps for a long time.

In addition to the recognition of environmental risk factors, and the consequent precautions to be taken to minimize the risks of contagion, it is equally important to take into account the aforementioned individual risk factors. It should therefore be remembered that some aspects of one’s lifestyle such assmoking, alcohol abuse, the presence of concomitant diseases or a weak immune system can increase the risk of infection in case of exposure to potential sources of contagion.

How to recognize it

If legionella is contracted, the risk of serious consequences, as we have seen, is concrete and timely recognition of the disease can be decisive to avoid complications.

However, this infection does not have peculiar characteristics that allow it to be clearly distinguished from a more common bacterial or atypical pneumonia. For this reason, the guidelines of the American Thoracic Society provide for a treatment based on antibiotics always active against bacteria of the genus Legionella even in case of mild community pneumonia and recommend to consider it among the possible causes in all nosocomial forms, until it is excluded through special laboratory investigations.

If circumstances require it, as may happen in these cases or in the presence of severe symptoms or known risk factors, the infection can be diagnosed by isolating the bacterium from respiratory secretion samples or by detecting the specific antigen in the urine.

Joycelyn Elders is the author and creator of EmpowerEssence, a health and wellness blog. Elders is a respected public health advocate and pediatrician dedicated to promoting general health and well-being.

The blog covers a wide range of topics related to health and wellness, with articles organized into several categories.

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