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Legionnaires Disease, Legionella, & Legionellosis FAQ

John A. Herbert
by John A. Herbert

This website does NOT provide medical advice, consult your local physician.

Here we have assembled some Frequently Answered Questions regarding Legionellosis, Legionnaires' Disease, and Legionella.

  • When was Legionnaires' Disease Discovered?
  • What is Legionnaires' disease?
  • What is Pontiac Fever?
  • What are the symptoms of Legionnaires' disease?
  • What is the prognosis and outcome for patients who have contracted Legionnaires' disease?
  • If I have contracted Legionnaires' disease, what are the chances that I will have a recurrence?
  • How is Legionnaires' disease diagnosed?
  • What are the common risk factors for Legionnaires' disease?
  • How is Legionnaires' disease treated?
  • Where does Legionella bacteria come from?
  • How do people contract Legionella?
  • How does Legionella escape the host defense of the patient and cause disease?
  • What have been the sources for Legionnaires' disease?
  • Where to find any Legionella code of practice or standards?
  • How can the risk of Legionnaires' disease infection be reduced?
  • What is Legionellosis?
  • What is Pontiac Fever?
  • What is next?

  • Legionella FAQ by building Legionella experts





    When was Legionnaires' Disease Discovered?

    In June 1976 a mystery illness emerged, primarily amongst patrons of an American Legion Conference held at the Stanford Hotel, Philadelphia USA.

    More than two hundred (200) people fell ill, and thirty four (34) died. A puzzled medical community frantically searched for answers. Eventually, in January 1977 the CDC (Atlanta, USA) announced that their research found a new bacteria that was responsible for causing the disease, it was named Legionella Pneumophila.

    Retrospect analysis of previously unexplained fatalities found that Legionella was not a new, the mysterious Legionella had struck in 1947 and again in 1953. The Legionella species was just a mystery bacterium finally identified.

    Later it was discovered that Legionella Pneumophila species comprised more 52 species and more than 70 different serogroups (2010 data) - Ever since its initial discovery, new species and subtypes are being identified.

    Legionella Pneumophila sub type one became known as LP Sp1,type Sp2, etc.

    There also another group of bacteria with similar characteristics Legionella Like Species have been uncovered. Known as LLAP (Legionella-Like Amoebal Pathogen) these bacteria are thought to be closely related to the Legionellae genus.



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    What is Legionnaires' disease?

    Legionnaires' disease (退 伍軍人病) is generally a severe potentially fatal pneumonia type illness caused by a bacterium from the Legionella species. Most often Legionella Pneumophila but other species also cause disease.

    Rapid urinary diagnosis test does NOT detect other Legionella Pneumophila sero types, or Legionellae species or LLAP.

    The name Legionella Pneumophila was identified from the first outbreak at the 1976 American Legion Convention in the Bellevue Hotel, Philadelphia, USA. The bacteria also causes a less severe flu like illness its named Pontiac Fever.



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    What are the symptoms of Legionnaires' disease?

    The incubation period of Legionnaires' disease can from two to ten days. It is the time it takes before symptoms of the illness appear after being exposed to the bacteria.

    For several days the patient may feel tired and weak.Most patients who are admitted to the hospital develop high fever often greater than 39.5°C (103°F).

    Cough can be the first sign of a lung infection. The cough may be sufficiently severe to cause sputum production (coughed up mucous). Gastrointestinal stomach symptoms are common with diarrhea being the most distinctive symptom.

    Many patients have nausea, vomiting, and stomach discomfort. Other common symptoms include fever, headaches, muscle aches, chest pain, and shortness of breath.


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    What is the prognosis and outcome for patients who have contracted Legionnaires' disease?

    If the patient is treated with appropriate antibiotics near the onset of the pneumonia, the outcome is good, especially if the patient has no underlying illness that compromises his/her immune system.

    For patients whose immune systems are compromised, including transplant recipients, delay of appropriate therapy can result in prolonged hospitalization, complications, or death.

    For those patients who are discharged from the hospital, many will experience fatigue, loss of energy, memory loss, and difficulty concentrating for several months after discharge from the hospital. Complete recovery can take up to one year.

    Post Legionella infections studies are rare, and anecdotal evidence from personal correspondence suggests that a survivors suffer longer than the medical professional believes.



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    If I have contracted Legionnaires' disease, what are the chances that I will have a recurrence?

    Contracting Legionnaires' disease a second time is extremely rare, however it is possible.

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    How is Legionnaires' disease diagnosed?

    Specialised laboratory tests are necessary and, unfortunately, may not be available in many hospitals. These include culture on specialized Legionella media. Culture media furnish nutrients for the bacterium. When sputum from the patients are placed onto the culture media, the bacterium grows on the medium and can be identified.

    Other tests include direct fluorescent antibody (DFA) in which the bacterium can be stained and becomes visible under a fluorescent microscope. Antibody testing is a blood test in which antibodies that are reactive against Legionella are present in the human body showing that the patient has come into contact with the bacterium previously.

    Urinary antigen is a test that detects Legionella in the urine.




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    What are the common risk factors for Legionnaires' disease?

    The most common risk factor is heavy cigarette smoking. However, chronic lung disease is also common. The most intense risk factor is organ transplantation, the medicine used to protect the new organ also compromise the patient's defense system against infection. Patients who take corticosteroid medicines are also at high risk.



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    How is Legionnaires' disease treated?

    Many antibiotics are highly effective against Legionella bacteria. The two most potent classes of antibiotic are the macrolides (azithromycin), and the quinolones (ciprofloxacin, levofloxacin, moxifloxacin, gemifloxacin, trovofloxacin).

    Other agents that have been shown to be effective include tetracycline, doxycycline, minocycline, trimethoprim- sulfamethoxazole. Erythromycin, the former antibiotic of choice, has been replaced by more potent and less toxic antibiotics.



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    Where do Legionella bacteria come from?

    Legionella are natural inhabitants of water, and can be detected at very low levels in rivers, lakes, groundwater, and streams. One species Legionella Longbeachae is different, it is found in potting soil / compost.


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    How do people contract Legionella?

    When the Legionella organism is concentrated and then aerosolized, for example in a shower, cooling tower or other aerosol device, minute water droplets containing Legionella are inhaled, and due to the small size, are drawn deep into the Lung. (click here to see the Legionella video).

    Another way of contracting Legionella is thought to be "Aspiration" although little evidence exists to support the supposition. Aspiration means choking such that secretions in the mouth get past the choking reflexes and instead of going into the oesophagus and stomach, mistakenly, enter the lung. The protective mechanisms to prevent aspiration is defective in patients who smoke or have lung disease. Legionella Longbeachae is also contracted by inhalation of bacteria from dust generated from soil and compost.



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    How does Legionella escape our own defences?

    Once the Legionella enters into the lung our own killer cells designed to help us fight infection, the white blood cells (macrophages) migrate towards the Legionella and attempt to engulf (phagocytose) with the goal to kill the Legionella cell. These alveolar (air sac) macrophages engulf the Legionella bacteria, however Legionella escapes the killing mechanism of the alveolar macrophage, instead of death the Legionella cell lives, thrives, and multiplies inside the macrophage. In hiding, it multiplies until the number of bacteria  physically rupture the wall of macrophage, the liberated bacteria are freely released into the lung to be engulfed by other cells, and the cycle of phagocytoses, multiplication, and release begins over again.

    Legionella is called an intracellular pathogen because of it multiplies within other organisms. The intracellular location of Legionella is also important in therapy. Many antibiotics effective against pneumonia are ineffective against Legionella because they do not penetrate the respiratory tract cells or alveolar macrophages.The modern antibiotics called the macrolides (azithromycin) or quinolones (ciprofloxcin, leveofloxacin, gemifloxacin and moxifloxacin) can penetrate cells and can then effectively kill Legionella.



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    What source/devices have been found to spread Legionella and Legionnaires' disease?

    Over the years, the number of confirmed cases, and the source device for confirmed cases have increased and wide ranging including:

  • Water distribution systems of large buildings, cooling towers, Hot water systems, air-conditioning equipment, fountains, showers, foot baths, grocery mist machines, humidifiers, nebulizers, whirlpool spas, and hot springs
  • Here is a list (PDF 3 pages 1994) summarizing past outbreaks and the associated device.

    click here for more information about Legionella sources

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    Legionella Code of Practice

    Here is a link: Click here to download the Hong Kong Prevention of Legionnaires’ Disease Code of Practice (PDF format 288K)



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    Soils and Compost Risks

    In addition to aqueous sources, the Legionella Longbeachae species is a dry type only found in compost, soil, and potting soil. Inhaling dust from this dry material is the route of infection. It is particularly common in Western Australia, with cases also reported in USA.

    Sero types Legionella Longbeachae Sp 1 and Sp 2 have so far been discovered.

    An unusual L. Longbeachae infection was reported following transplant operation, so it is not solely limited to soils and compost.


    How can the risk of Legionnaires' disease infection be reduced?

    Information is the most important weapon, arrange for regular building audits. Kelcroft's audit provides a roadmap to help you and your team lower the risk of infection stemming from your property.......learn more

    What is Legionellosis?

    Legionellosis is a medical term to describe any type of illness cause by the Legionellae genus.

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    What is Pontiac Fever?

    The Legionella bacterium can also causes a less severe illness named Pontiac Fever. Pontiac fever causes influenza type illness, hospitalisation should be required.


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    What Next?



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    Keywords: Legionella FAQ