What are Legionnaires' disease and Pontiac fever?

Legionnaires' disease (also called legionellosis) is an uncommon infection caused by a bacterium (germ) called legionella. There are two types of illness which can develop after being infected with this bacterium:

• Legionnaires' disease. This causes a pneumonia (lung infection). It is usually a severe illness, sometimes fatal.
• Pontiac fever. This is when the bacteria cause a flu-like illness. It is not usually serious.

Some background about legionella bacteria

In 1976 an outbreak of pneumonia occurred among American legionnaires (ex-servicemen) who attended a conference. 221 people developed pneumonia, and 34 died. A bacterium (germ) that had never been identified before was found to be the cause and was namedLegionella pneumophila (pneumophila means lung-loving). Since then, many different types of Legionella bacteria have been identified. Legionella bacteria live in fresh water and mud and are found all over the world. Most cases of illness are caused by L. pneumophila, the type first identified.

How do you get Legionnaires' disease or Pontiac fever?

Outbreaks that affect many people occur from time to time

The source of the bacteria in an outbreak is usually a man-made water distribution system where the bacteria have multiplied in great numbers. Warm storage tanks where the water stagnates are ideal for legionella bacteria to multiply. The bacteria thrive in water temperatures between 25° and 45°C - about 35°C seems to be the optimum temperature. This means that Legionnaires' disease can be caught from:

• Piped water, especially hot water, in large buildings where long runs of pipe work can be a source of the bacteria.
• Circulating water droplets in air-conditioning and cooling systems, cooling towers and evaporative condensers.
• Whirlpool spas (jacuzzis), other warm-water baths and shower heads.
• Decorative fountains.
• Nebulisers and humidifiers (including some types of breathing equipment) if topped up with contaminated tap water.
• Potting compost.
• Plastics factories.

You become infected by breathing in water droplets (aerosol) that are contaminated by many legionella bacteria. An outbreak can affect many people in the same hospital, hotel, office complex or other large building, around the same time.

Sporadic (individual) cases

Individual cases occur from time to time. Where only one person is infected, then the source of the bacteria is not usually found. About 2 in 100 cases of pneumonia that occur in previously well people are thought to be due to legionella bacteria.

Risk factors for developing Legionnaires' disease

Anyone can develop Legionnaires' disease. However, you are more likely to develop Legionnaires' disease (and pneumonia caused by other bacteria) if you are already in poor health. Conditions that make you more at risk of Legionnaires' disease, and more at risk of a serious illness if you contract Legionnaires' disease include:

• Chronic lung disease. This includes asthma and especially chronic obstructive pulmonary disease (COPD) and lung cancer.
• Other chronic (long-term) conditions such as chronic kidney disease (CKD), heart disease or diabetes.
• Alcohol dependence.
• Cancer - especially lung cancer or leukaemia.
• Conditions or situations which affect or suppress your body's natural immune responses and ability to fight infection, such as:
  • Diabetes.
  • Long-term steroid medication.
  • Human immunodeficiency virus (HIV) infection or acquired immune deficiency syndrome (AIDs).
  • Immunosuppressant medication. This includes chemotherapy given for cancer, some medications given for rheumatological (joint) conditions or diseases such as Crohn's disease and medications used if you have had an organ transplant. Examples include: azathioprine, mycophenolate (CellCept®), ciclosporin (Neoral®), tacrolimus, rituximab and interferon.

You are also more at risk of contracting Legionnaires' disease if you are a smoker and if you are aged over 50 years.
Note: person-to-person spread of Legionnaires' disease does not occur. This means that you cannot catch Legionnaires' disease from an infected person. You cannot catch Legionnaires' disease from drinking contaminated water either. To get the illness you need to inhale water droplets that contain legionella bacteria.

What are the symptoms of Legionnaires' disease?

• The incubation period is normally 2-10 days (but it can be up to 2 weeks). This means that symptoms start 2-10 days after first being infected On average, the incubation period is 3-6 days.
• Typical first symptoms are: cough, fever (high temperature), sweats, shivers, being off food, and feeling generally unwell. Headaches and aches and pains are common. Your sputum may become yellow/green, and is sometimes bloodstained.
• Symptoms tend to become worse quite quickly as the infection spreads through the lung tissue. You may become breathless, breathe fast, and develop a tight chest. You may have pain in the side of the chest when breathing (pleuritic pain). These are typical symptoms of pneumonia. (See separate leaflet called'Pneumonia' for more information.)
• Common non-lung symptoms include confusion, nausea, vomiting, diarrhoea and loss of appetite. About 3 in 10 people have symptoms that affect the gastrointestinal tract (the gut).
• Complications develop in some cases and can cause heart, brain, kidney or blood problems.

How is Legionnaires' disease diagnosed?

A chest X-ray can confirm that you have pneumonia. However, pneumonia is common and there are many bacteria and other types of germs that can cause pneumonia. (Legionnaires' disease is an uncommon cause of pneumonia.)

Blood tests and sputum tests are then done to try to identify the bacterium or other germ that is causing the pneumonia. These tests are called cultures because the idea is to try to get the legionella bacteria to grow and multiply, so it can be identified under a microscope. More specialised blood tests can look for antibodies against legionella bacteria in the blood. Antibodies are proteins made by the immune system, which fight infection.

In addition, if Legionnaires' disease is suspected, a urine test can confirm most (but not all) cases of legionella infection. The test, called the legionella urinary antigen test, detects a specific protein that is part of the legionella bacterium. These proteins can be detected in the urine, even several months after you have been treated for Legionnaires' disease.

Sometimes a lumbar puncture (LP), sometimes called a spinal tap, is performed to help diagnosis. Here, a sample of cerebrospinal fluid (CSF), or spinal fluid, is removed from the base of the spine, using a needle and some local anaesthetic to numb the area. CSF is the fluid that flows around the brain and spinal cord, to protect and nourish the nerve tissues. The CSF is tested to see if the legionella bacteria have infected the brain (if this has happened, it is known as meningitis). This test is only rarely done, mainly if you are very unwell, to exclude other serious illnesses, particularly those caused by infections. (See separate leaflet called 'Lumbar Puncture' for more information.)

What is the treatment for Legionnaires' disease?

• You will normally be admitted to hospital.
• Antibiotics are started as soon as possible. Usually they are given intravenously (IV), which means into a vein, rather than by mouth (orally). The traditional antibiotic to treat Legionnaires' disease (or suspected Legionnaires' disease) is erythromycin. But other antibiotics are often used - for example: azithromycin, clarithromycin, levofloxacin, ciprofloxacin or doxycycline. If you are pregnant, erythromycin and azithromycin are safe for the baby. Sometimes a combination of antibiotics is used, if it is not yet certain whether the infection is due to legionella or to other bacteria. Normally, you will need at least a 10- to 14-day course of antibiotics to treat Legionnaires' disease properly.
• Oxygen is commonly given.
• IV fluids are often given to keep you well-hydrated. If you are very unwell, especially with a breathing problem such as pneumonia, you will be unable to drink enough fluids.
• Intensive care with supportive treatments, such as assisted ventilation, may be needed if the pneumonia is severe.

What is the prognosis (outlook)?

Legionnaires' disease is a serious illness. If you were previously fit and well, you have about a 1 in 10 chance of dying from Legionnaires' disease. If you were previously unwell, (for example, if you already have a lung disorder) then you have a higher risk of dying if you get Legionnaires' disease.

Possible complications of Legionnaires' disease include:

• Respiratory failure. This means your lungs are unable to provide the body with enough oxygen. The pneumonia has affected the lungs to such a degree that normal ventilation cannot occur. In these situations you will need help with breathing, and supplemental oxygen. You might need to be treated in a high-dependency or intensive care unit. It is possible that you might need to be anaesthetised (put to sleep) and intubated (have a breathing tube inserted), whilst you are very unwell.
• Renal (kidney) failure. Severe infection can stop the kidneys from working. The kidneys usually filter and clean the blood. When there is renal failure, there is a toxic build-up of waste products in the blood. Chronic renal failure is treated with dialysis but, during an acute infection, the blood can be cleaned constantly by flowing through a haemofiltration machine.
• Septic shock. In very severe infections, the blood pressure can drop suddenly and dramatically. Infection can overwhelm the body and affect all parts of it. It can affect the blood clotting too, and lead to catastrophic bleeding problems. There is a high chance of death with septic shock and overwhelming sepsis (infection).

The outlook is best if the illness is diagnosed as early as possible, and you are treated with antibiotics immediately.

After recovery from Legionnaires' disease, you may get symptoms such as tiredness, poor concentration, cough or mild shortness of breath. These may take several months to settle.

What are the symptoms and treatment of Pontiac fever?

Pontiac fever is a milder illness caused by legionella bacteria. It causes a flu-like illness which lasts just a few days. Symptoms include: fever, shivers, headache, muscle aches, tiredness and a dry cough. However, the infection does not affect the lungs and therefore does not cause pneumonia. Usually, no treatment is needed other than paracetamol or ibuprofen to ease fever and muscle aches.

It is not clear why some people get Legionnaires' disease (with pneumonia) and some people get the milder Pontiac fever when infected with legionella bacteria. 

It is also thought that some people who are infected with legionella bacteria do not become ill at all (a subclinical infection).

Can infection with legionella bacteria be prevented?

As mentioned, the main cause of outbreaks of Legionnaires' disease is from contaminated water sources. In the UK, and in many other countries, there are regulations on how to maintain water supplies and air conditioning systems used in large buildings. This keeps the number of legionella bacteria very low to minimise the risk of infection. However, it is very difficult to eradicate this bacterium completely. If you are an employer or a landlord, you have a legal duty to ensure all water systems in your premises are properly maintained.

If you have a home humidifier or spa, follow the manufacturer's advice about maintenance and cleaning.

About 3 in 10 cases of Legionnaires' disease are contracted abroad, usually due to poorly maintained water storage and air conditioning systems in hotels. Always mention any recent foreign travel if you are unwell and see your doctor.

At present, there is no vaccine that can protect against legionella bacteria.