Legionnaires’ disease (legionellosis)

Legionnaires’ disease (legionellosis) is a bacterial respiratory infection that may or may not involve pneumonia.

It is caused by Legionella bacteria. These bacteria can multiply in stagnant water and at warm temperatures, for example in water pipes. They enter the airways in the form of microscopic water droplets (aerosols).

Older people, people who are chronically ill and people with an immune deficiency are most at risk of becoming infected with Legionnaires’ disease. Smoking also increases the likelihood of becoming infected.

The term Legionnaires’ disease also refers to pneumonia caused by Legionella bacteria. It should be treated with antibiotics and hospitalization is usually necessary.

There is also a mild form of legionellosis known as Pontiac fever. This is similar to a flu infection and usually clears up by itself within a few days.

Infection with Legionella bacteria can be associated with symptoms similar to a flu infection. In this case, it is known as Pontiac fever. The symptoms usually appear within 5 hours to 3 days of infection. Those affected usually have

• a dry cough
• a headache
• aching limbs

If the Legionella bacteria cause pneumonia, this is known as Legionnaires’ disease and the symptoms are far more serious. They appear within 2 to 10 days of infection and typically include the following:

• sudden high temperature and shivering
• severe feeling of discomfort
• shortage of breath (dyspnea)
• coughing and sputum

Further symptoms such as stomach pain, diarrhea and confusion are also possible. 

Legionnaires’ disease is caused by infection with Legionella bacteria. The bacteria are transmitted via aerosols, mists of microscopic water droplets containing the pathogen, and enter the airways when inhaled.

Legionella bacteria can multiply in water systems or pipes if the water remains in them for a long time and has a temperature of between 25°C and 45°C. Potential sources of infection include taps, showers, jacuzzis, humidifiers and cooling systems.

Older and poorly maintained hot water systems in particular provide favorable conditions for the bacteria to grow and form a “biofilm” of slime in the water pipes. 

In addition to infection via aerosols, in rare cases, infection is also possible if water containing the pathogens accidentally enters the windpipe instead of the esophagus when swallowed. However there is no risk of infection when drinking the water in the normal way as Legionella bacteria are killed by gastric acid in the stomach. Infection from person-to-person is also almost unheard of. So people who have been infected do not pass the infection on to others.

In recent years, over 2,000 cases of Legionnaires’ disease have been reported in Germany each year. Within Europe, 4.5% of all cases of pneumonia where infection occurred outside a hospital were caused by Legionella bacteria. However, it should be assumed that not everyone with pneumonia is tested for Legionella, so the actual number of cases of infection will be higher.

Most cases of Legionnaires’ disease only affect one person, but minor outbreaks with a single source of infection are occasionally reported, for example in hotels or on cruise ships. More cases of Legionnaires’ disease (legionellosis) occur in summer and autumn than in winter and spring.

The people most at risk of Legionnaires’ disease include:

• elderly people
• people with immune deficiencies
• people with diabetes and chronic heart disease or pulmonary disorders
• smokers

Men are two to three times more likely to be infected than women.

It is particularly important to prevent Legionella bacteria from reproducing in water systems. The proper construction and appropriate maintenance of water systems are of general importance.

Water pipes in residential buildings should be used regularly. Basins full of stagnant water (reservoirs) as well as dead-end pipes resulting, for instance, from disconnecting a sink or moving a basin, should be avoided.

Legionella bacteria struggle to multiply when temperatures fall below 20 degrees or rise above 55 degrees; they die at temperatures above 60 degrees. The temperature control on central boilers in residential properties should therefore be set to a minimum of 60 degrees. The water should have a minimum temperature of 55°C throughout the hot water pipe system. Cold water pipes should be insulated so that the water in them does not heat up, for example due to higher temperatures in summer. 

Devices that atomize water, producing aerosols, should be regularly cleaned and stored in a dry condition. Examples of such devices include humidifiers.

There is no vaccination against Legionella.

Doctors will ask the patient questions and perform physical examinations in order to diagnose Legionnaires’ disease (legionellosis). If pneumonia is suspected, the lungs are sometimes X-rayed. However, these scans alone are unable to definitively determine whether a patient has Legionnaires’ disease. 

To definitively diagnose an infection with Legionella, several laboratory methods are therefore used. In many cases, Legionella can be detected using rapid urine tests. It is also possible to take sputum (phlegm) and use it to grow a culture in a laboratory on special growth media. A “PCR” test can also be used to detect Legionella DNA in the sputum.

Legionnaires’ disease with pneumonia should be treated with bacteria-inhibiting antibiotics as quickly as possible. Treatment in hospital is often necessary. In many cases, fluoroquinolone antibiotics such as levofloxacin or moxifloxacin are used. Alternatively, macrolide antibiotics, such as azithromycin or clarithromycin, can be prescribed. Doctors often administer these intravenously.

Treatment takes 1 to 2 weeks, sometimes longer. If the treatment is effective, most people make a full recovery from Legionnaires’ disease (legionellosis) with pneumonia. In up to 10% of cases, however, the infection is fatal. This makes it particularly important to start the treatment as quickly as possible.

People with Pontiac fever do not need to be treated with antibiotics.