Legionellosis, also known as Legionnaires’ disease, for decades it has been the pathology caused by the Legionella Pneumófila bacterium. Find out all about it here.

This is a bacterial infection due to the agent Legionella pneumophila and originally identified in 1977. This happened when 34 people died in an outbreak of pneumonia. For this reason, they called it “Legionnaires’ disease.”

Currently, there are two clinical and epidemiological forms this bacterium causes. The first was Legionnaires’ disease, this being the pneumonic form. Second is the non-pneumonic form “Pontiac fever.”

Likewise, around 42 species and 64 serotypes of this bacterium have been studied. Serotype 1 is responsible for 90% of legionellosis cases. Find out everything about this disease below.


Legionellosis is a bacterium that lives especially in areas of America, both in the north and in the south. Australia, Africa and also Europe are also places where it can appear.

This bacterium tends to adhere especially to natural sources of water such as lakes, streams, rivers and hot springs since it has very diverse living conditions in various types of environments. Its amount to be pathological in the recipient is more than 10,000 CFU / mL. under a temperature ideal for its reproduction, of 25 to 45 ° C.

The incidence of nosocomial pneumonia caused by Legionella pneumofila depends on the degree of colonization of the hospital water distribution systems

The bacteria will also be dependent on hosts that are susceptible to being a recipient of the bacteria. Therefore, those patients who suffer from severe immunity damage, and also:

  • HIV patients.
  • Transplanted people.
  • Leukemia patients.
  • People who have had recent surgeries or have been assisted with ventilatory breathing.


In its entirety, the transmission route of Legionella is airborne, through droplets of saliva that people involuntarily expel when speaking, sneezing and even laughing. Another form of transmission is through aerosols, which expel droplets that can be easily inhaled.

Through inhalation, the bacteria will get to the lungs, and affect the alveoli, release toxins, and cause infection. There is no description of an evidence of contagion that occurs through person-to-person contact.

However, elderly people (such as the elderly) who have comorbidities such as alcoholism, smoking or have a weak immune system have predilection for susceptibility to this disease. This does not mean that healthy people are free from infection.

When should you suspect of legionellosis?

In those cases of pneumonia that are directly related to important epidemiological data, such as if the person has recently traveled, had hospitalizations or been in large gatherings.

Many cases of Legionella infection are directly in association with ventilatory respirators. For this reason, it should be explored whether there has been direct contact with this type of assisted breathing system or not.


  1. Lung form

  • Cough with mucopurulent sputum.
  • Pleuritic chest pain.
  • Thermal rises of 39 ° C.
  • Hemoptysis.
  • Dyspnoea.
  1. Extrapulmonary form

  • Cellulitis.
  • Pleuritis.
  • Sinusitis.
  • Peritonitis.
  • Pericarditis
  • Myocarditis.
  • Pyelonephritis.


The definitive diagnosis will depend on the isolation of the microorganism in direct immunofluorescence media by staining the tissue plus detection of antigens of the bacterium Legionella serotype 1 in urine.

The polymerase chain reaction culture medium is also useful, which shows the level of reproduction it has had since infection. If necessary, doctors will request a sputum culture, which will determine with good precision whether it is this nosocomial bacterium or not.

Legionellosis treatment: antibiotic

  1. Macrolides

It has broad antibiotic properties that have become the standard treatment that has been used since the discovery of Legionnaires’ disease. Erythromycin is its parent drug, which requires progressively large volumes of infusion and is administered intravenously.

The subsequent ones in the macrolide line are also what doctors recommend, such as: azithromycin, roxithromycin and josamycin that are really effective and that are for oral administration.

  1. Fluoroquinolones

Doctors prefer prescribing it in forms that manifest as severe infections. Levofloxacin and ofloxacin are the active principles as a complete treatment that covers the symptoms left by the bacteria. However, its use should be moderate due to the resistance that quinolones have had over the years.

If you suspect that you may be suffering from legionellosis, do not hesitate and visit your doctor. Only he can diagnose you and indicate the best treatment for the disease.

Don’t forget to SHARE everything you now know about legionellosis with your friends and family on your social networks!