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Legionellosis is the set of syndromes caused by the bacteria of the genus Legionella . Legionella pneumophila is the species most often responsible for infection in man.

This was discovered as a result of an intensive investigation that followed an epidemic outbreak of pneumonia that emerged among attendees at the annual convention of the American Legion (Legionnaires’ disease), held in Philadelphia in 1976. There were 180 cases of pneumonia, with high mortality.

Retrospective studies revealed that the same bacterium had been isolated in 1947 and that it constituted the causal agent of a benign, non-pneumonic “flu” that occurred in the city of Pontiac in 1968 ( Pontiac fever ).

Since then, legionellosis has become a relatively common disease, causing mostly sporadic or epidemic pneumonia. Less frequently, it is responsible for a non-pneumonic and “flu-like” fever and sporadic extra-respiratory infections.

What are the causes

Produced by the bacteria of the genus Legionella. Within this genus there are 41 species, with Legionella pneumophila being the species most often responsible for infection in man.

Legionella pneumophila is characterized by being:

  • A bacillus that does not stain or stains poorly with the Gram stain,
  • lives in the air or in free oxygen,
  • it is not acid resistant alcohol,
  • it is difficult to isolate in culture, and
  • stains with specific fluorescent antibodies.

Legionella pneumophila is widely distributed in nature and requires a high degree of relative humidity. It usually lives in the waters of rivers and lakes and in chlorinated drinking water, including that of the taps and showers of the general network.

Legionella species are spread suspended in aerosols, and man acquires the disease through the respiratory route: person-to-person transmission is not accepted. In the face of continuous exposures, it must be admitted that the disease occurs when the bacterial attack is qualitatively or quantitatively important or when there are factors in the host.

Legionellosis is more common in summer and fall. Its distribution is universal.

The mean age of patients with legionellosis ranges between 55 and 60 years.

The risk factors for this disease are not exactly known, but there is no doubt that it occurs more frequently in smokers, alcoholics and those who appear to be diseases that involve defects in respiratory defense mechanisms. The most common underlying diseases in infected patients are chronic obstructive pulmonary disease, cardiovascular disorders, alcoholism , diabetes mellitus, kidney diseases, neoplasms of all kinds, kidney and heart transplants, hairy cell leukemia, autoimmune diseases and processes treated with glucocorticoids.

Legionnaires’ epidemics occur, usually in institutions that share a water network or a common air conditioning distribution system, such as hotels, hospitals, or factories. In these systems, it has often been possible to detect the existence of one or more points where humidity and temperature allow a great development of Legionella, which is later spread by mechanisms that form aerosols (showers, air conditioning systems). It is acquired mainly by respiratory route. Legionella attaches itself to the epithelial cells of the respiratory system. Macrophages engulf Legionella, which is not destroyed but proliferates.

It is a disease that affects multiple organs. Two ways are known:

  1. No lung involvement (Pontiac fever): rapid and spontaneous resolution, without the need for antibiotic treatment; it only requires treatment of symptoms. It has an incubation period of 36 hours. It is characterized by fever, headache, and severe muscle aches.
  2. Legionnaires’ disease requires antibiotic treatment. The incubation period is 2 to 10 days. The episode begins with nonspecific symptoms, characterized by general malaise, muscle aches, headaches, dry cough , chills, and constant high fever. The picture progresses in 48 hours, appearing respiratory symptoms, such as fatigue, chest pain, purulent sputum and hemoptoic expectoration.

They can appear along with the above symptoms:

  • digestive disorders (watery diarrhea, nausea and vomiting, abdominal pain and jaundice ),
  • neurological (alterations in the level of consciousness, headache, hallucinations, seizures, difficulty in speech and meningeal alterations …),
  • kidney (kidney failure, glomerulonephritis and acute tubular necrosis ),
  • others ( pericarditis , myocarditis, endocarditis , eye injuries, etc.).

Legionella diagnosis

It can be done in various ways:

Laboratory diagnosis : various changes occur, such as:

  • increased leukocytes,
  • decrease in sodium and phosphorus,
  • increased transaminases , bilirubin, alkaline phosphatase and creatinine,
  • appearance in urine of protein and blood.

Radiological diagnosis : the findings are nonspecific.

Diagnosis according to the cause : using various techniques:

  • Culture,
  • direct fluorescence,
  • Polymerase chain reaction,
  • determination of antibodies,
  • determination of antigens in urine, sputum and serum.


The antibiotic of choice in Legionella is erythromycin. In patients severely affected by Legionnaires’ disease, the combination of rifampin plus a macrolide or quinolone is recommended as initial treatment.

How to avoid it?

The best way to prevent Legionella is to avoid the proliferation of the responsible bacteria in reservoirs of warm water, as well as all the mechanisms that can produce, from said water, an aerosol that favors its inhalation.

In the hot water network, it is necessary to avoid the existence of areas where the water can remain stagnant or where chlorination or temperature cannot prevent bacterial proliferation, as well as to repair all the structural defects of the cooling towers that allow the production of aerosols. .

The most effective measure to prevent Legionella outbreaks is to hyperchlorinate the drinking water of the institution where such outbreaks occur. In addition, it is convenient to raise the temperature of the hot water network to achieve water temperatures in the taps above 55-60 ºC. In taps or showers that are used infrequently, it is necessary to carry out a system of periodic opening of the water.

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Hello Readers, I am Nikki Bella a Psychology student. I have always been concerned about human behavior and the mental processes that lead us to act and think the way we do. My collaboration as an editor in the psychology area of ​​Well Being Pole has allowed me to investigate further and expand my knowledge in the field of mental health; I have also acquired great knowledge about physical health and well-being, two fundamental bases that are directly related and are part of all mental health.

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