LEGIONELOSE - Symptoms, Transmission and Treatment

Legionellosis, also known as legionnaires' disease, is a potentially serious infection caused by a bacterium called Legionella pneumophila .Legionellosis is an non-contagious infection, which is usually acquired through the inhalation of water particles contaminated with the Legionella bacteria and can lead to atypical pneumonia.

In this article we will explain what is Legionnaires' disease, how is it transmitted, what are its symptoms and what are the treatment options.

We will address only legionellosis, a serious form of atypical pneumonia. If you are looking for information on the classic form of community-acquired pneumonia caused by bacteria other than Legionella pneumophila , access the following text: PNEUMONIA |Symptoms and Treatment

What is Legionnaire's Disease?

Legionellosis is an infection that was only recognized in 1976 following an outbreak of pneumonia among participants in a convention of American legionnaires, a group of US veterans. The convention was held at a Philadelphia hotel whose central air conditioning system was contaminated by

Legionella pneumophila .Just one week after the convention, 130 participants had already been hospitalized and 25 had died with a strange picture of chest pain, shortness of breath, cough and fever.

The origin of the disease was only recognized months later, after intense investigation by the American department of health. Both the disease and its causative agent, unknown to science until that time, were baptized in honor of legionaries who became ill.

The discovery of Legionella pneumophila and its form of propagation has brought about a radical change in the hygiene and safety standards of air conditioning and water systems in general. However, despite the care, dozens of new outbreaks of legionellosis have continued to occur around the world since the disease was identified. There are even cases of transmission within hospitals. The most recent outbreaks occurred in Portugal, Germany, Australia and the USA.The most widespread outbreak so far has occurred in Spain in 2001, with about 450 confirmed cases.

Since its identification, knowledge about legionnaires' disease has increased considerably. We know today that legionellosis is transmitted through the air, through droplets contaminated with water, and can cause severe pneumonia, especially in the most debilitated, such as the elderly, immunosuppressed or patients with previous lung disease. The bacteria Legionella pneumophila can also cause a milder picture, called Pontiac's disease, which closely resembles the common cold( read: FLU, Symptoms, Treatments, and Vaccine).

Some literature sources call Legionellosis any Legionella infection, including mild forms. In this article we will refer to the serious form of the disease just like legionellosis or legionnaires disease. The mild form will always be called Pontiac's disease. I will make this distinction so that there is no confusion, since Pontiac disease is a benign form, which does not present with pneumonia or risk of death.

Forms of Transmission of Legionnaire's Disease

As noted in the first paragraph of this article, legionellosis is not a contagious disease. There is no transmission from one person to another, so patients hospitalized with legionellosis do not need to be in isolation. If you have a relative or friend diagnosed with legionnaires' illness, your concern should not be with the recent contact you had, but rather with the type of environment in which both were present recently.

The transmission also does not appear to occur through ingestion of water. You do not get legionellosis by drinking water, but rather by aspirating contaminated water particles present in the air. Let's explain in more detail.

A Legionella pneumophila is a bacterium that lives in aquatic environments, including lakes and streams. However, in the natural sources of water, the amount of Legionella existing is very small, being low the risk of contamination. The bacteria seems to really like it is artificial water reservoirs. Places where water is stored, with mild temperatures( 25 to 42ºC), such as pipes and reservoirs, are ideal for multiplying Legionella. The presence of other aquatic microorganisms such as algae, amoebas, ciliate protozoa and other bacteria also help promote the growth of Legionella.

A multitude of water systems have long been identified as potential sources of legionellosis. Among the most common are heating or cooling systems, central air conditioners, hot tubs, showers, high pressure water equipment, humidifiers, fountains, artificial fountains, nebulizers, steam saunas, etc. Any environment where there is vaporization or emission of water particles can be a source of contagion, if, of course, the water is contaminated with the bacteria.

Just to illustrate, there have been described cases of legionnaires' disease that were acquired because of fountains in luxury hotel lobbies, hot tubs in spas and even club pools. Some cases of legionellosis acquired in hospitals occurred because the water pipeline was colonized with the bacteria. There is also a case described in Italy of legionellosis contracted in a dental office, through contaminated water on the high pressure instruments that the dentist used to wash patients' mouths during their procedures.

The use of copper pipes and the presence of chlorine in the water greatly reduces the risk of colonization by Legionella pneumophila .Water systems of large establishments, including residential or commercial buildings, shopping malls, hospitals, clubs, hotels, etc., must undergo systematic checks on the quality of water from their tanks and pipelines. Outbreaks usually occur when there is negligence in controlling water quality in community settings. If your building's plumbing or water tank is contaminated, you can contract legionellosis by taking a simple shower.

Despite the frightening picture that the above explanations may be painting, the fact is that legionellosis is a relatively infrequent disease, especially if we take into account that billions of people around the world are exposed daily to water aerosols. A recent study found that in Europe, the rate of legionellosis is approximately 10 cases per year for every 1 million people. In Brazil there are no clear epidemiological data, but if we extrapolate the existing rate in Europe, we have an estimated 2000 cases per year.

It is also important to note that not everyone who is exposed to the bacterium Legionella pneumophila ends up developing the most severe form of disease. The infection rate is only 5%.Therefore, 95% of people exposed to the bacteria do not develop legionnaires' disease. Within this 95% group, a good deal of Pontiac disease goes unnoticed, as if it were an ordinary flu.

Legionellosis is uncommon in young, healthy people. The main risk factors for legionnaires' disease are smoking and chronic obstructive pulmonary disease - COPD( see: COPD | COPD and chronic bronchitis).Age over 55 years, excessive consumption of alcohol, diabetes mellitus or immunosuppression( HIV, chemotherapy, use of corticosteroids. ..) are also factors that facilitate the onset of the disease.


Pneumonia is the most typical manifestation of legionnaires' disease. The incubation period is on average 2 to 10 days.

In the early days of illness, the condition is usually mild, with dry cough, malaise, muscle pain and headache, similar to any common respiratory virus. From the second day, the picture begins to worsen. The cough becomes more intense and the sputum can be accompanied by blood( read. The picture progresses with a high fever, generally above 39ºC, chest pain, shortness of breath and prostration. Gastrointestinal symptoms may also be present, including diarrhea, vomiting, and abdominal pain.

Laboratorially, the patient may have an increase in the number of leukocytes in the blood, changes in renal function( read: EXAMINATION OF CREATININE AND UREIA), changes in the liver function tests( read: WHAT DOES TGO, TGP, GT RANGE AND BILIRUBIN?and hyponatremia( low blood sodium levels).Blood in the urine is also common, but it is usually microscopic, only detectable through urinalysis( read: URINE EXAMINATION | Leukocytes, nitrites, hemoglobin. ..).

Patients with legionellosis often need hospitalization and the mortality rate ranges from 5 to 30%.

Pontiac Disease

Pontiac disease, as already explained, is a much more benign infection. The causative bacterium is the same, but the clinical picture is completely different.

Unlike Legionnaire's disease, Pontiac's disease has a much shorter incubation period, ranging from 1 to 3 days. The clinical picture is of fever, malaise and headache. Cough with sputum usually does not occur and patients do not develop pneumonia. Rarely, there is a need for hospitalization and the infection cures spontaneously in 100% of cases.

Diagnosis of Legionnaires

The rapid diagnosis of Legionnaire's disease is essential, since the early initiation of adequate treatment is clearly associated with a better evolution of the condition.

The level of suspicion should be high, as Legionella pneumophila is not usually identified in the tests usually done to diagnose common pneumonia.

For the diagnosis of Legionnaire's disease, two tests are usually ordered:
- Urine soluble antigen search.
- Culture of respiratory secretions.

Both exams cited above are not part of the initial investigation of common pneumonia. Therefore, if the doctor does not think about legionellosis, he will not make the diagnosis early because he will not ask for the necessary tests.

Treatment of Legionnaire's Disease

Treatment of legionella pneumonia should be done with antibiotics. As discussed earlier, the earlier the antibiotic was started, the greater the chance of successful treatment. In milder cases, the patient may be treated with oral antibiotics at home. In more severe cases, hospital admission is necessary and antibiotic treatment is done intravenously.

The two most commonly used antibiotics for the treatment of Legionnaires' disease are levofloxacin or azithromycin( read: AZITROMYCIN | Indications and side effects).In both cases, the treatment is done for 7 to 10 days. In immunosuppressed patients, or in those with very severe conditions, 21 days of antibiotic therapy may be required.

Patients with Pontiac disease, ie without Legionella pneumonia, do not need hospitalization or antibiotics. The infection behaves like an ordinary virus and cures spontaneously after a few days without leaving any kind of sequelae.

To date there is no vaccine against Legionella.