Legionnaire’s Disease


What is Legionnaire’s disease?

A bacterium called Legionella that causes an acute respiratory infection and be found in freshwater environments or in other complex water systems such as:

  • Water supply systems
  • Water pipes (pipes with a little water, with corrosion and salts, shower heads)
  • Heating and cooling systems
  • Hot or cold water tanks such as swimming pools, hot tubs, fountains but also natural hot water tanks for example thermal baths etc.
  • Mechanical devices such humidifiers or medical devices that use running water

Environments with temperatures of 20-45°C are ideal conditions for Legionella to grow and multiply. Of the many different strains of the bacterium, legionella pneumophila is the strain associated with the human illness, presenting in two clinical forms called Legionnaires’ Disease and Pontiac Fever.1,2

Legionnaire’s disease can present

  • Sporadically: when it is not connected to a particular source
  • In outbreaks: when two or more people are sick in the same area at the same time.

Depending on the environment in which it presents, it can be distinguished as:

  • Hospital Legionnaires’ disease: when hospitalized for the past 2-10 days
  • Traveler Legionnaire’s disease: when a trip has taken place over the previous 2-10 days.

Modes of transmission2

  • By inhalation of contaminated water droplets
  • By ingestion of contaminated water, although this is rare
  • Human-to-human transmission is extremely rare

Risk Factors2

Not everyone who is exposed to Legionella will get ill. People at risk for getting sick from Legionella include:

  • Ages> 50 years old
  • Smoking: Smokers and ex-smokers
  • Chronic respiratory disease for example, Chronic Obstructive Pulmonary Disease
  • Diabetes
  • Renal, Hepatic insufficiency
  • Cancer
  • Immunosuppression due to disease or treatment (ie. chemotherapy, radiotherapy)

Legionnaire’s Disease (Legionella Pneumonia)1,2

Incubation period of this illness is ~2-10 days. Legionella Pneumonia is a serious pneumonia that requires hospitalization with a mortality rate of 1-10%. However, early treatment with antibiotics has significantly improved the prognosis and outcome of the disease.
SYMPTOMS: fever, cough, shortness of breath, headache and nausea, diarrhea, confusion. Symptoms begin 2-10 days after exposure.
DIAGNOSIS: Chest X-ray, urine test, bacterial culture in sputum (prior to antibiotic treatment)
TREATMENT: antibiotics with macrolides or fluoroquinolones while also treating the symptoms

Pontiac Fever1,2

Less severe, it usually resolves in 3-5 days. Symptoms may begin within a few hours of exposure, with flu-like symptoms such as fever and muscle aches. No specific medical treatment is needed except for symptoms treated with antipyretic analgesics.


Prevention is based on regular management and treatment of complex water systems to keep Legionella from growing. The following is important for controlling outbreaks:

  • Regular cleaning and management of all complex water systems
    • With use of water disinfectants (ie. chlorination, ionization, hydrogen peroxide, ultraviolet radiation)
  • Search for the source of the original outbreak and treat immediately with either:
    • Chlorine treatment or
    • Heat shock

Monitoring and Surveillance1

In Greece there is a diligent system for monitoring and controlling the quality of water resources and water supply facilities through multiple parameters including the search for toxic substances and pathogenic microorganisms. Audits of water systems are made systematically throughout the country and especially in tourist areas. The recent cases of Legionnaire’s disease in Greece are the first ever reported and are considered sporadic and not attributed to a specific source. The European Centre for Disease Prevention and Control is also regularly updated.3

Recording, monitoring and reporting Legionnaire’s Disease is obligatory in Greece and is completed by a special form of the Ministry of Health and the Hellenic Center for Disease Control and Prevention (HCDCP) for the effective epidemiological surveillance of the disease.



  1. Κέντρο Ελέγχου & Πρόληψης Νοσημάτων. ΝΟΣΟΣ ΤΩΝ ΛΕΓΕΩΝΑΡΙΩΝ/ΛΕΓΕΩΝΕΛΛΩΣΗ. http://www.keelpno.gr/el-gr/νοσήματαθέματαυγείας/λοιμώδηνοσήματα/νο%CF. Accessed August 2, 2018.
  2. Centers for Disease Control and Prevention. Legionella (Legionnaires Disease and Pontiac Fever). https://www.cdc.gov/legionella/about/index.html. Published 2018. Accessed August 2, 2018.
  3. European Centre for Disease Prevention and Control. European Legionnaires’ Disease Surveillance Network (ELDSNet). https://ecdc.europa.eu/en/about-us/partnerships-and-networks/disease-and-laboratory-networks/eldsnet. Accessed August 2, 2018.