Legionella is a disease that never left. It's always been out there. 

Even in New York City, there was recently a Legionella outbreak in the summer of 2015, which was the worst in the city's history. Twelve died and over 120 were infected, apparently because of a contaminated water cooling system - not involve tap water or the water drunk in New York. An outbreak also took place in Flint, Michigan, after their water systems were contaminated.

It should be said that just because a bacteria is present, it doesn't mean it's a risk. Not all who are exposed are infected. Legionella may be present in cooling towers without there actually being any infections.

It's a disease that's always out there. As doctors, we regularly see sporadic cases. It is diagnosed throughout the US and the world - every year. Usually a few cases are diagnosed, but outbreaks of 100 or more, as seen in New York, remain very rare.

What is Legionella?

Legionella is a bacteria that spreads from water. A person is infected by inhaling or aspirating warm water. This can lead to a very serious pneumonia.

It's pronounced LEE-juh-nell-a

What does it cause?

There are two diseases caused by Legionella bacteria.

Legionnaire's Disease can cause a serious illness with a lung infection, pneumonia. This can cause fever, cough, shortness of breath, and chest pain, much like a pneumonia caused by other infections.

It will also often cause headache and muscle aches.

However, this pneumonia can be more serious than others. It can lead to death in at least about 1 in 20 cases (5%). More will die if they are already ill. In some outbreaks, as many as 3 in 10 (30%) will die.

Some will require intubation and ventilation to help them breathe, meaning they will need a machine to help them breathe while they are fighting the infection.

Many will need to be in an intensive care unit. It can cause kidney failure in some.

Pontiac Fever causes a mild flu-like illness with fever, muscle aches, headaches. It happens in healthy people. It does not cause pneumonia or the severe illness like Legionnaire's disease. It is not does not cause death.

Who is at risk?

We are all exposed to water, but certain people are at more risk.

These characteristics include:

  • Smoker
  • Older (over 50)
  • Male
  • On steroids (like prednisone)
  • On other immunosuppressive drugs
  • Kidney disease
  • Liver Disease
  • Diabetes
  • Chronic Lung disease (like COPD)
  • Immunocompromised (such as HIV/AIDS, hematologic malignancy, or other cancer)

The disease is also associated with certain water exposures, such as whirlpool spas or hot spas. Those who've traveled recently or who've had repairs on their home plumbing are a risk. Multiple infections have been traced back to cruise ships. There have also been outbreaks within hospitals.

How does it spread?

Legionella spreads when warm water that is sprayed or aerosolized is inhaled or aspirated.

The bacteria then spreads within our lungs.

The bacteria can be found in water, naturally. The bacteria actually live within amoebas that live in the water. Legionella will live inside of amoebas – such as NaegleriaAcantaoemoeba, and others.

​The bacteria tend to be found (like the amoebas) more in warm water. This can be a hot tub or whirlpool or in a hot water tank. They can be found in cooling tanks for air conditioners, the pipes of a building, or a large fountain in a park. Although infections often spread from air conditioners, this does not occur from home units in windows or those in cars.

The bacteria can also be found in compost and soil.

Can it spread from person-to-person?

No. It has not been shown to do this.

Doesn't it spread in hospitals?

The water systems of hospitals can become contaminated with Legionella, just like in any building. This is particularly unfortunate as those who are already ill are at the most risk of serious disease. It does not spread from a patient to visitors or to nurses, doctors, and other health professionals.

When do symptoms start?

Symptoms of Legionnaire's disease usually start 2-14 days after being exposed. Pontiac Fever develops in 24-72 hours after exposure.

How is it diagnosed?

The disease is not always diagnosed. When it is diagnosed, diagnosis may come late and specialized treatment may be delayed. The symptoms of the disease (fever, cough, chest pain) are not specific to Legionella alone. Legionella pneumonia patients seem like other pneumonia patients, just sicker. It's hard for a clinician to know that this is Legionella pneumonia and not another pneumonia (like Strep Pneumo or influenza).

To specifically diagnose Legionella, many standard tests - such as a sample of sputum looked at under a microscope - will not identify Legionella. Culture often misses the bacteria. Instead a very specific test, like the Legionella Urine Antigen test, has to be ordered. This means diagnosis is quicker if the clinician suspects Legionella; without suspecting the infection, it is harder to diagnose.

How is it treated?

Treatment requires specific antibiotics (fluoroquinolone or macrolide, such as levofloxacin or azithromycin). These antibiotics may be prescribed anyways. However, these antibiotics might not be prescribed. As diagnosis is often delayed or not made, a patient may not have the antibiotics, which can be life-saving, that they need.

How common is it?

It is thought that 8,000 to 18,000 people are hospitalized with Legionnaires' disease annually in the US. It is likely under diagnosed.

Where is it found?

It is found in much of the world - from North America to Africa, Europe and to Asia, Australia, and South America. 

What is done to prevent it?

The bacteria has spurred a number of improvements in the management of water systems. There have been a number of different means of protecting against Legionella, but many solutions are not perfect - such as heating water or flushing out pipes with hot water, or using chlorination or UV light.

Because the bacteria is found in water and soil in nature it is hard to avoid it.

What was the largest outbreak?

​The largest known outbreak occurred in Spain in 2001 (June 26 to July 19). More than 800 suspected cases were reported; 449 of these cases were confirmed; 1% died.

Why is it called Legionnaires' disease?

The first outbreak was identified in 1976 among attendees of and American Legion convention at a hotel in Philadelphia. Within a week after the 3-day convention, over 130 out of the 2000 attendees were in hospitals and 25 had died. It took until January 1977 to identify the bacteria responsible - which was named legionella as it struck Legionnaire's. The hotel's air conditioner water cooling tower system was identified as the source of the bacteria. Before that the bacteria had only been seen in laboratories and was thought to only infect animals.

Pontiac fever was first identified in Pontiac, Michigan earlier in the 1970s.

Are there different types of Legionella?

Yes. Legionella pneumophila is the most common species, causing 90% of illnesses. Legionella pneumophilia serotype 1 causes about 85% of cases. It is thought that different species and serotypes may cause different severities of illnesses. There are over 50 species and 70 serotypes. Some tests may miss less common types of Legionella. Some tests may miss rare types of Legionella.

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