Synonyms
Legionellosis, Pontiac fever (attenuated course)
Definition
Legionnaires’ disease is the result of infection with Legionella pneumophila, an aerobic (with oxygen) living, gram-negative rod bacterium, which has its disease significance for humans living in large hot water systems. In Germany there are about 400 cases of the disease per year. In the USA, where the legionnaire’s disease was first described, it is assumed that 90,000 cases occur every year.
In healthy people, about 20% of the disease is fatal, while in patients with a weak immune system, about 70% can be fatal. Pontiac fever is not fatal. In 1976, at the annual meeting in a hotel in Phiadelphia of members of a US war veterans’ association, a good 180 cases of severe pneumonia occurred, resulting in the death of almost 30 people.
Research into the cause of the disease was conducted, which was followed by the discovery of the previously unknown bacterium Legionella pneumophila. The name “Legionnaire’s disease” was given because it mainly affected US veterans, but also a few other hotel guests. The milder Pontiac fever was already described after an outbreak in the city of Pontiac in 1968, without any pathogen being detected at that time.
Legionella pneumophila/Legionnaire’s disease is a germ that occurs everywhere in the environment in soil and water, and finds favorable living conditions in warm, stagnant waters. Important for this are poorly used warm water systems of larger buildings, air conditioning systems, but also air humidifiers, the use of which can produce an infectious aerosol that is responsible for the pneumonia of the lung support and interstitial tissue (interstitial/atypical pneumonia) typical of Legionnaires’ disease. In larger buildings, such as hospitals, mechanisms are in place to disinfect the hot water, such as heating the system in sections to over 70°C for a few minutes, using chemical additives such as chlorine, filter systems or ultraviolet light.
After 2 to 10 days of incubation, flu-like symptoms (see influenza) occur rapidly, such as muscle pain, fever, some of them above 40°C, chills and headaches. A dry to slightly bloody cough, nausea, vomiting and diarrhea occur. If the brain is inflamed at the same time, disturbances of consciousness must also be expected.
With Pontiac fever, the pure flu-like symptoms are in the foreground, but pneumonia does not occur. The symptoms develop after one or two days and last for about a week. As a not frequent disease, Legionnaires’ disease is partly a diagnostic challenge.
The anamnesis of risk factors, such as the recent use of little-used showers or air conditioning systems in older large buildings, but also whirlpools, indoor fountains and aquariums are possible sources of infection. In addition to the unspecific, flu-like symptoms, interstitial pneumonia, which can be detected by x-ray, is an indication that further limits the circle of causes of the disease. Blood culture is not successful, but legionella in sputum can be detected directly by means of a fluorescent antibody marker under the microscope, or after cultivation on a special culture medium.
Since not all patients have sputum, a sample would have to be taken by rinsing the lungs. Alternatively, legionella antibodies can be searched for in the urine, or the legionella genetic material can be detected from blood, urine or sputum by polymerase chain reaction, whereby the detection from sputum is most significant. If detected, the legionnaire’s disease must be reported.
Legionnaire’s disease can be treated well with antibiotics. Quinolones or macrolides are used. In severe cases a quinolone can be combined with a macrolide, or a macrolide with rifampicin for two to three weeks.
There is no vaccination against Legionella pneumophila. The risk of infection in modern, large European buildings is unlikely due to the disinfection systems, even though, for example, a shower that has not been used for a long time or the whirlpool already mentioned can pose a health risk if water hygiene is inadequate, but this risk is not limited to the germ Legionella pneumophila. In countries with lower standards of hygiene, to reduce the risk of illness in a hotel complex, the hot water of the shower can be left running for five to ten minutes, during which time the room must be left to avoid inhaling potentially infectious aerosol.Particularly vulnerable persons with a reduced immune system defensive capacity, such as the elderly, AIDS sufferers, otherwise immunocompromised patients such as chemotherapy patients, as well as patients with chronic lung disease have an increased risk of developing full-blown Legionnaire’s disease instead of the milder Pontiac fever when exposed to Legionella.
This group of persons should avoid places with a risk of infection. If suspected in time and antibiotics are administered in time, the prognosis for legionnaires’ disease is favorable. If the immune system is severely impaired, however, the disease does not lose its dangerousness and remains potentially fatal. The course of Pontiac fever is similar to that of a flu-like infection.
