Legionnaire's Disease

By Wendy Innes. May 7th 2016

The recent outbreak of this disease in Europe has lead many people to want to know more about this exotic-sounding disease. What is it? How do you get it? Is it fatal? The truth is that it is a disease that has been around for a long time, and while it can be fatal if left untreated, it usually isn't.

However, this doesn't mean that it isn't serious. According to the Centers for Disease Control and Prevention (CDC), between 8,000 and 18,000 people are hospitalized with Legionnaire's disease every year, though they acknowledge that many more cases go undiagnosed or unreported.

What Is It?

Legionnaire's disease is a type of atypical pneumonia. The disease is caused by the bacterium Legionella pneumophila. The people who are most susceptible to a Legionella infection are the elderly, smokers, and those with compromised immune systems.

The Legionella bacterium was discovered in 1976 after several of the people who were attending the American Legion convention in Philadelphia became ill. Though it certainly existed before 1976, because it is a type of pneumonia, it was treated like any other type of pneumonia. However, it is diagnosed much more frequently now due to the fact that if a patient presents pneumonia-like symptoms, they are automatically screened for Legionella.

Legionnaire's disease is not a contagious disease, meaning it is not spread from one person to another. Rather, most people who contract this illness do so by inhaling the bacterium from the air.

Legionella bacterium also causes a condition called Pontiac fever. Pontiac fever is a milder illness and the two conditions are often referred to as Legionellosis. The big difference is that Pontiac fever will usually clear up on its own, while Legionnaire's disease can be fatal without treatment. Even after treatment, some people still experience lingering problems.


The cause of Legionnaire's disease is infection from the Legionella pneumophila bacterium. This bacterium can live outdoors in soil and water, although the majority of cases occur indoors from contaminated water. Sources include things like hot tubs, air conditioners, and the misting systems in the produce department at supermarkets. Plumbing systems in large buildings have also been the source of some Legionella outbreaks, mainly because these systems are quite complex and can allow bacteria to grow easily. Other sources include:

  • Cruise ship hot tubs and pools
  • Decorative fountains
  • Cooling towers in air conditioning systems
  • Water systems in hospitals, nursing homes and hotels
  • Physical therapy equipment, particularly equipment involving water

It is unclear how much exposure is required for a Legionella infection to occur. Some people have developed infections after just a few minutes of exposure.

Legionella, unlike many other bacteria, have a relatively large area in which they can cause infection. Most infections occur within a fairly small radius from where the bacteria can be found. However, Legionella can spread up to four miles by air and still cause infection.

Legionella is primarily spread through aerosolized water droplets in the air, but that is not the only way that it is transmitted. It can also be transmitted through:

  • Aspiration: this occurs when someone chokes on something they are eating or drinking. Microscopic water droplets can enter the lungs this way and cause infection.
  • Soil: water droplets in soil can be dispersed in the air when gardening or at construction sites.


Legionnaire's disease has an incubation period of approximately 14 days, after which time someone who is infected with Legionella will begin to show signs, including:

  • Headache
  • Chills
  • Fever that could reach 104 F or higher
  • Muscle pain

After the first 48 hours, additional symptoms may emerge, including:

  • Chest pain
  • Shortness of breath
  • Cough, which may bring up mucus or blood
  • Loss of appetite
  • Fatigue
  • Nausea, vomiting or diarrhea
  • Confusion or other cognitive problems

While Legionnaire's disease primarily affects the lungs, it also affects those who are already suffering from a medical condition and can affect other parts of the body like the heart if someone already has a damaged heart.

Pontiac fever may also produce symptoms, typically headache, fever and chills, but it does not infect the lungs like Legionnaire's disease does and the symptoms will clear up in 2 to 5 days.


Though Legionnaire's disease is a serious condition, the treatment is relatively simple. Once a diagnosis is made through blood tests, urine tests and x-rays, a Legionella infection can be treated with antibiotics. The type of antibiotic used will vary from person to person. If a person was relatively healthy when he contracted Legionnaire's disease, the antibiotics used to treat that person are of a different class than those used on someone who has recently been on a course of antibiotics and still contracted the infection. This is done to prevent the Legionella from becoming resistant to the drugs.

After having treated Legionnaire's disease, it is recommended that a person get a pneumonia vaccine. This is also recommended for anyone with a suppressed immune system, young children and the elderly.

While it is fairly simple to treat, Legionnaire's disease is quite serious and, if left untreated, it can result in death. So it's important to take any flu-like symptoms seriously and see a doctor right away. It could be a matter of life or death.


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