Legionnaires’ Disease – Causes, Symptoms & Treatments

legionnaires disease

Legionnaires’ disease is a severe form of pneumonia caused by Legionella bacteria. It’s the most well-known form of Legionellosis – the family of Legionella infections, which includes Pontiac and Lochgoilhead fever.

Unlike other strains of Legionellosis, Legionnaires’ disease can prove fatal, which explains its notoriety.

This infamy is helped by Legionella bacteria being widespread and present in most bodies of water and soil.

Infection risks in the wild are almost nonexistent, however. Legionella is much more dangerous when it finds its way into human-made water systems, where the bacteria thrive if conditions are right.

If you’re concerned about Legionella or are responsible for water systems, this guide examines the causes, symptoms and treatments of Legionnaires’ disease. It also explores the conditions that let bacteria grow and put people at risk.

Where Legionnaires’ Disease Comes From

As mentioned, Legionnaires’ disease is a pneumonia, a catch-all term for lung inflammation caused by bacterial infection. It was first identified in 1976 following an outbreak at an American Legion convention in Philadelphia, USA. It’s this event that gives the disease its name.

Legionella bacteria is the strain linked to Legionnaires’ disease, and the pathogen is commonly found in freshwater.

Thankfully, you’re unlikely to catch Legionnaires’ from a natural water source. Like most bacteria, Legionella prefers warmer temperatures than those seen in freshwater systems, so grows slowly when exposed to the elements.

Infection is also caused by inhalation of infected water droplets, not contact or even ingestion. Situations that allow this specific transmission route are rare in wild freshwater bodies.

Risks are much higher when Legionella is in a human-made water system. Water is often stored at optimal temperatures for bacterial growth. Specific devices, such as cooling towers, spread infected water droplets. The greater concentration of Legionella bacteria and increased inhalation risks make infections much more likely in built environments.

Legionella Awareness Training

Need training for Legionella to control the risk of this bacteria at work? Human Focus offers an online Legionella Awareness Training course, which is designed to examine the health risks associated with legionella bacteria and ways to control it to ensure safety for all.

Sources of Infection

Any poorly maintained water system is a possible home for Legionella, but infection risks increase if:

  • Water is maintained between 20°C – 45°C (Legionella’s preferred temperature range)
  • Water is re-circulated or stored within the system
  • Substances that feed bacterial growth (rust, sludge, organic matter, etc) are in the system

Risks are even higher when water systems are large and complex, as they’re harder to monitor and maintain.

Familiar sources of infection include:

  • Showers
  • Hot tubs
  • Decorative water features
  • Cooling towers (a type of heat exchanger that cools water in large buildings)
  • Heating Ventilation and Air Conditioning (HVAC) systems

These devices generate breathable water droplets (aerosols), which creates a severe infection risk if Legionella is present in the attached water system.

Where Legionnaires’ Disease Comes From

People who have contracted Legionnaires’ disease generally don’t pass the infection on, so it’s not necessary to isolate or avoid patients.

Other Causes of Legionnaires’ Disease

Legionnaires’ disease is almost exclusively caused by breathing in water droplets containing Legionella bacteria. This makes drinking from infected sources relatively low risk (although still ill-advised).

Extreme caution is necessary because it’s still possible to contract the disease when drinking. Coughing while consuming infected water can cause aspiration – commonly described as liquid ‘going down the wrong pipe’. This reaction allows Legionella bacteria to enter the lungs, triggering an infection.

Workplace Legionella Risks

Legionella is more likely to grow in non-domestic water systems that tend to be larger and more hospitable to the bacteria. Because of this heightened risk, employers, building managers and others in control of premises must assess and manage Legionella risks. This duty is enforced by the Health and Safety Executive, which provides information about the disease and guidance for duty holders on its website.

Symptoms of Legionnaires’ Disease

The Legionnaires’ disease symptoms are largely interchangeable with those of pneumonia. They also overlap with general flu symptoms. A lack of distinct symptoms makes Legionnaires relatively tricky to spot. It may contribute to a theorised overall underdiagnosis of the illness.

Signs of the disease include:

  • A persistent cough
  • Shortness of breath for no apparent reason
  • Chest pain, particularly when breathing or coughing
  • A high temperature or fever (over 40°C)
  • Headaches
  • Fatigue and muscle aches
  • Nausea or vomiting
  • Diarrhoea

These symptoms generally develop two to three days after exposure to Legionella bacteria. It can take up to two weeks in rare cases.

You may be tempted to ignore these signs, mistaking them for flu-like symptoms. But it’s essential to seek medical advice if:

  • A cough has lasted for more than three weeks
  • Coughing brings up blood
  • Breathing or coughing is particularly painful

You should be especially wary if you spent time in a hospital, hotel or cruise ship shortly before experiencing symptoms. These locations have sprawling and complex water systems where Legionella flourishes (along with a higher concentration of hot tubs).

Risk Factors

You’re not guaranteed to develop an illness when exposed to Legionella bacteria. And if you do, you may develop the less dangerous Pontiac fever, which rarely needs treatment.

However, there are risk factors that make you more vulnerable to Legionnaires’ disease and its effects, including:

  • Smoking (which makes you more susceptible to any lung infection)
  • Having a compromised immune system
  • Having an existing lung condition such as emphysema

You’re also at greater risk if you’re 50 or above, as it naturally becomes more challenging to resist infections in old age. Young children are also at greater risk due to their underdeveloped immune systems.

Treatment of Legionnaires’ Disease

Legionnaires’ disease is treatable with antibiotics and fatalities are rare. Hospitalisation may be required for more severe cases, however.

Hospital treatment can include:

  • Intravenous antibiotics
  • Oxygen
  • Use of a ventilator to help with breathing

Anyone hospitalised will probably need to continue taking antibiotic tablets after they’ve returned home.

Most people fully recover, but it may take multiple weeks. No vaccine currently exists, so the only way to protect against infection is by limiting bacterial growth and preventing the spread of infected aerosols.

Legionella Awareness

If you’re an employer or are in charge of a building or work with water systems, you have a duty to manage Legionella infection risks and prevent the spread of Legionnaires’ disease.

Our online Legionella Awareness Training course explores the conditions that let bacteria grow, infection hazards and symptoms of Legionnaires’ disease. It also outlines effective risk controls needed to make water systems safer. This knowledge helps duty holders comply with regulations and prevent disease outbreaks in their workplace or building.

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Jonathan Goby
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