In legionellosis (synonyms: Legionella pneumophila infection; Legionella pneumophila infection without pneumonia; Legionellosis; Legionellosis with pneumonia; Legionellosis without pneumonia; Legionnaires’ disease; Legionnaires’ pneumonia; Pontiac fever; ICD-10-GM A48. 1: Legionellosis with pneumonia; ICD-10-GM A48.2: Legionellosis without pneumonia [Pontiac fever]) is an infectious disease caused predominantly by the bacterium Legionella pneumophila.
The Legionella pneumophila species is responsible for approximately 90% of Legionella pneumonias.
Legionella bacteria are found in water-bearing systems. They find ideal conditions at temperatures between 25 and 45 °C. However, they also multiply at temperatures between 50 and 60 °C, and growth of Legionella pneumophila can be assumed to occur particularly in this temperature range. However, they do not survive temperatures above 60 °C for long periods or above 70 °C for short periods.
Several forms of legionellosis can be distinguished:
- Legionnaires’ disease (legionellosis with pneumonia/pneumonia) – Legionellosis refers to a complex of flu-like symptoms with pneumonia.
- Pontiac fever (legionellosis without pneumonia) – Pontiac fever is an acute respiratory infection with fever, cough and muscle pain without pneumonia.
- Pittsburgh fever (caused by Legionella micdadei) – Pittsburgh pneumonia occurs predominantly in immunocompromised individuals.
Furthermore, one can distinguish community-acquired from nosocomial (hospital-acquired) legionellosis.
Seasonal accumulation of the disease: Legionellosis occurs clustered in summer (due to increased travel activity increases the risk of infection) and autumn.
Transmission of the pathogen (route of infection) occurs by inhalation of the pathogen-containing water (as an aerosol) through domestic or public water systems such as showers, whirlpools, etc.
Human-to-human transmission: very likely possible.
Incubation period (time from infection to onset of disease) is usually:
- Legionnaires’ disease (legionellosis with pneumonia): about 2 to 10 days (median: 6 to 7 days).
- Pontiac fever (legionellosis without pneumonia): approximately 5 to 66 hours (median: 24 to 48 hours).
Sex ratio: males are more commonly affected than females.
Frequency peak: The disease occurs mainly from middle age (50-70 years). Affected are mainly immunocompromised persons, the elderly, people with chronic diseases such as renal insufficiency (kidney weakness) and smokers.
The incidence (frequency of new cases) is approximately 0.8 cases per 100,000 inhabitants per year.
Course and prognosis: The course of Legionnaires’ disease is more severe than that of Pontiac fever and can become life-threatening.
The lethality (mortality based on the total number of people with the disease) for Legionnaires’ disease is between 5% and 15% in previously healthy individuals, untreated. In immunocompromised individuals or people with chronic diseases, the lethality can be as high as 70%.
In Germany, direct or indirect detection of the pathogen is reportable under the Infection Protection Act (IfSG) if the evidence indicates an acute infection.
