Where are Legionella bacteria most commonly found?

Legionella lives in bodies of water, both marine and inland (ponds, rivers and lakes), because bacterial growth requires high humidity and a high concentration of carbon dioxide. It can also enter municipal water supply systems, cooling towers, thermal pools, domestic water and sewage systems, solar installations, fire protection systems and air humidifiers.

Where can Legionella bacteria grow?

Bacterial colonization is favored by temperatures ranging from 25 to 45°C (the optimum temperature for their growth is 38°C), low disinfectant concentrations, stagnant water and biotic factors such as the presence of other microorganisms and biofilm. They most often multiply in standing water (e.g. in water supply systems), where contaminants (limescale, rust and algae) appear and provide nourishment for Legionella.

How can you become infected?

Infection with Legionella bacteria occurs primarily through inhalation, by breathing in aerosols (while in a shower cubicle, near a city fountain or a sprinkler).

The smaller the water droplets, the greater the chance that the bacteria will reach the lower respiratory tract. Legionella infection can also occur through choking on water, although this is relatively rare.

IMPORTANT!!!

Drinking water contaminated with Legionella bacteria does not lead to infection. The bacteria are not transmitted from person to person, so a patient does not pose a risk to those around them, as is the case with viruses.

Legionellosis – bacterial incubation period

The incubation period for Legionnaires’ disease (Legionella pneumonia) is 2–10 days. In rare cases, the first symptoms appear after 20 days. In the case of Pontiac fever, the bacterial incubation period ranges from five hours to three days (most often 24–28 hours).

Legionellosis – symptoms

Legionellosis most often occurs in two forms: Legionnaires’ disease and Pontiac fever. In Legionnaires’ disease, Legionella symptoms appear suddenly and begin with malaise, muscle pain and a fever of 39–40°C. Other common symptoms include diarrhea, severe headaches, cough, difficulty breathing, chest pain, chills and altered consciousness. The first symptoms may be observed 2–10 days after infection. The most common consequence of Legionella infection is the pulmonary form of the disease. The extrapulmonary form is much rarer. Its course is considerably milder and, unlike the pulmonary form, it does not involve a runny nose or sore throat. Instead, symptoms associated with infection of other organs are characteristic: inflammation of the heart muscle and serous membranes, and impaired or damaged kidney and liver function. In this case, deaths of patients are most often reported.

The second form of legionellosis mentioned above is Pontiac fever. Its symptoms resemble ordinary influenza: headache, fever, muscle aches, chills and a feeling of weakness. Vomiting, diarrhea and nausea occur less frequently. Symptoms usually resolve spontaneously after 2–5 days. Pontiac fever occurs in outbreaks; individual cases occur sporadically.

Legionellosis – main risk factors among patients

The main risk factors that may contribute to Legionella infection include:

  • age over 40,
  • heart disease,
  • diabetes,
  • weakened immunity,
  • alcoholism,
  • smoking,
  • lung disease,
  • kidney disease,
  • cancer,
  • lymphomas,
  • respiratory diseases.

People who have undergone transplants or surgical procedures are also in the risk group.

Legionellosis – diagnostic methods

Because Legionella bacteria multiply inside macrophages, they are difficult to detect in clinical samples. Diagnosis of Legionella pneumonia most often uses bronchial washings, bronchoalveolar lavage or lung tissue biopsies, which means that sputum is the material collected. The sensitivity of such tests ranges from 20 to 80 percent.

Another diagnostic method is the qualitative detection of total antibodies against L. pneumophila antigens. A urine immunochromatographic test can also detect the Legionella antigen. Bacterial culture is another diagnostic method, but it takes 4 to 10 days to grow, significantly extending the wait for results.

Legionellosis – treatment

Treatment of legionellosis depends on whether the patient has been diagnosed with Legionella pneumonia or Pontiac fever. Legionnaires’ disease requires antibiotics, which are started as soon as a risk of its development is identified, even before diagnostic test results are confirmed. This can minimize the risk of complications.

Some infected people make a full recovery. Some require hospitalization, mainly older people and patients with comorbidities. In hospital, they can receive immediate assistance — they often need intravenous electrolytes to prevent dehydration accompanying the disease or to reduce breathing difficulties.

The recovery period depends on how quickly treatment is initiated. Pontiac fever does not require treatment because it resolves spontaneously.

Legionellosis – is it fatal?

Legionellosis can be fatal. A high number of deaths is most often recorded among patients with comorbidities (heart, lung or immune system diseases).

Can Legionella infection be prevented?

There is no vaccine available for Legionnaires’ disease. However, the disease can be prevented by properly disinfecting potential sources of Legionella bacteria, including:

  • cleaning cooling towers,
  • regularly emptying and cleaning swimming pools and hot tubs,
  • using chemical treatments with chlorine in pools and spas,
  • keeping hot-water systems above 60°C and cold-water systems below 20°C.

It is worth remembering that Legionella bacteria can develop in air-conditioning systems, so they should be cleaned regularly.