More Information on Legionellosis

Legionellosis is an acute infectious disease that is caused by Legionella and is associated with two clinically and epidemiologically distinct illnesses: Legionnaires’ disease and Pontiac fever. Legionnaires' disease is characterised by pneumonia (Legionella pneumoniae pneumoniae). Pontiac fever produces a milder flu-like, non-pneumonic illness.

Causative agent of the disease
The causative agent is a is a rod-shaped, Gram-negative, aerobic non-spore-forming bacterium in the Legionellaceae family. The genus Legionellae comprises 48 species of Legionellae with 39 serogroups of Legionellae which are virulent to humans. In Europe, Legionellosis is mainly caused by L. pneumophila.

The bacterium L. pneumophila was first identified in mid-seventies, as the cause of an outbreak of severe pneumonia in a convention centre in the USA in 1976, resulting in 221 cases and 34 deaths. In 1977, microbiologists at the United States Centre for Disease Control isolated Gram-negative bacteria from the lungs of a patient who died during the outbreak and proved by serological methods that they were the causative agents of the disease. This micro-organism was later named Legionella pneumophila (pulmonary Legionella). Retrospective analysis of blood serum from patients with pneumonia of uncertain origin in different countries showed that Legionella had previously caused outbreaks in America and Europe. L. pneumophila was subsequently isolated from environmental samples during the investigation of outbreaks of Legionellosis in various countries around the world. The first case of pneumonia caused by Legionella bacteria in Lithuania was diagnosed in 1985 (retrospectively).

Modes of transmission
Human infection with legionellosis typically occurs through the inhalation of aerosols containing Legionellae. Drinking or cooking with contaminated water does not lead to infection. Infected person does not transmit the disease.

Legionella bacteria are widespread within the natural water environment (rivers, lakes, ponds and reservoirs), can be found in soils and sludge, and may grow in hot and cold water systems in industrial and public facilities. Sludge and rust deposited in water systems facilitate the conditions for Legionella growth. The most favourable water temperature for Legionella multiplication is between 20 °C and 45 °C. Below 20 °C and above 60 °C Legionella do not multiply. Legionellosis is more prevalent in developed countries with high levels of thermal water generation, cooling, recirculation, air conditioning and other technologies.

The most common sources of Legionella are air conditioners, chillers, compressor rooms, showers, swimming pools, and various medical equipment (especially respiratory therapy). Industrial factories and meat processing plants can be sources of accumulation and spread of Legionella. In these types of production facilities, the abundant use of water and aqueous aerosols creates favourable conditions for the growth and transmission of Legionella.

Older people are more susceptible to this infection than the young. Smoking, chronic lung disease and immunodeficiency status are significant risk factors for Legionellosis.

Pontiac fever. The incubation period ranges from a few hours to two days. Symptoms include fever lasting 2 to 6 days, accompanied by head aches and muscle aches, and a dry cough.

Legionnaires' pneumonia (Legionnaires' disease). Incubation period spans from 2 to 10 days. Typically, the disease onset involves high fever, fatigue, headaches, and muscle aches. Dry cough and pleuritic chest pain progress to severe pneumonia. Approximately 30% of patients experience diarrhea or vomiting, while around 50% may develop unconsciousness and hyponatraemia (Schwarz-Bartter syndrome). Chest X-rays often reveal bilateral alveolar infiltrates, as well as segmental or lobar infiltrates. About one-third of patients exhibit a small amount of fluid in the pleural cavity. The resorption of pulmonary infiltrates is slow, taking 1-4 months. Pulmonary fibrosis develops in 25% of cases, although rales in the lungs are rare. The causative agent is not visible in sputum smears (does not stain with Gram's method), and there are few leukocytes present.

Prevention of Legionellosis involves identifying the reservoir of the causative agent and employing thermal or chemical methods for its inactivation, ensuring proper maintenance of air conditioning, cooling, and humidification systems, enhancing medical professionals' knowledge in diagnosing Legionellosis, and promoting public education and training.

Residents are advised to prevent water stagnation and regularly clean showers, showerheads and taps regularly to avoid the build-up of deposits.

The main measures to reduce the risk of Legionellosis include maintaining water systems effectively: maintaining hot water temperatures between 50-60ºC; ensuring cold water temperatures do not exceed 25ºC; preventing water stagnation in systems; cleaning and disinfecting cooling towers and pipes in air conditioning systems at least twice annually; cleaning and disinfecting water heaters and filters; and disinfecting hot water systems following water heater repairs and prior to the heating season.


Last updated: 29-03-2024