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Legionnaires’ disease: Things to Know about This Potentially Fatal Lung Infection

Legionnaires’ disease can lead to failure of vital organ systems in the body, or even death. Learn its causes, symptoms, risk factors, treatment, and preventive measures.

A Quick Overview of Legionnaires’ disease and Its History

Legionnaires’ disease (LD) is a serious infection of the lungs (pneumonia). It causes breathing problems, fever, chills, headache, and chest pain. A bacterium known as Legionella pneumophila causes this infection.

The Centers for Disease Control and Prevention (CDC) discovered legionella in 1976. Back then, the CDC was investigating an outbreak of severe pneumonia among people who had attended the American Legion Convention in Philadelphia. Hundreds of participants of the convention developed severe lung infections. Among them, 30 died due to the infection.

Later, the CDC found that the bacterium had spread through the air conditioning system of the hotel where the participants had stayed.

Legionella can also cause a milder illness called Pontiac fever. It does not cause life-threatening complications. The symptoms of Pontiac fever resemble those of the flu.

Collectively, Pontiac fever and Legionnaires’ disease are called legionellosis.

What is Legionella? Get the Facts

Legionella is a species of bacteria present in the environment. Among them, L. pneumophila is found in natural and artificial water systems.

These include lakes, rivers, creeks, and hot springs. Besides, hot water systems, ice machines, air-conditioning cooling towers, hot and cold water taps, showers, nebulizers, spa baths and spa pools, hydrotherapy pools, ornamental fountains, and home birthing pools are also known to contain Legionella.

Legionnaires’ disease Symptoms

Most cases occur in the warmer months as the bacteria grow well in warm temperatures. In fact, more than 50 percent of the legionellosis outbreaks have occurred between April and October.

The incubation period of Legionnaires’ disease is two to ten days. This means a person usually experiences the early symptoms within two to ten after exposure to the bacteria.

The illness begins with the following signs and symptoms:

  • A headache
  • Pain in the muscle
  • Chills
  • Fever that is usually higher than 104°F

As the illness progresses, an affected person may have:

  • A dry cough, however, sometimes it may contain mucus or blood
  • Problems with breathing
  • Chest pain
  • Upset stomach including nausea, diarrhea, and vomiting
  • A decreased appetite
  • Weakness
  • Mental confusion
  • Seizures

Typically, these symptoms appear by the second or third day

Causes of Legionnaires’ disease

A type of bacteria called legionella causes Legionnaires’ disease. People can get ill by breathing in the bacteria present in the droplets of water in the air.

There have been reports of cases of illness due to exposure to the contaminated soil. Nonetheless, such cases are rare. Most notably, the infection does not spread from person-to-person contact.

What is at Risk of Contracting Legionnaires’ Disease?

Most healthy people do not become ill even when they have the bacteria in their body. However, the risk is higher among people who:


Smoking is a well-known risk factor for several respiratory conditions including Legionnaires’ disease. Studies suggest that both smoking, as well as exposure to secondhand smoke, can significantly increase the risk.

In addition, the risk may also be higher among people who smoke cannabis and former cigarette smokers.

Have weakened immune systems

As with any other disease, having weakened immune systems is a major risk factor for Legionnaires’ disease.

People with HIV/AIDS and those who take certain medications that suppress the immune system have a significant risk of contracting this illness.

Have long-term lung diseases

People with chronic lung conditions may be more likely to contract the illness. For example, those with chronic obstructive pulmonary disease (COPD) and damaged air sacs in the lungs.

Have other long-term diseases

The risk is higher among people with diabetes, cancer, liver diseases, or kidney disorders.

Are older than 50 years of age

Though Legionnaires’ disease can affect any person irrespective of the age, it is more commonly reported in older adults. People younger than 20 years of age rarely get ill with the legionella bacteria.

Legionnaires’ disease Treatment: Know Your Options

Treatment with antibiotics is necessary in almost every case. Prompt antibiotic therapy is key to reducing the risk of complications and death. In fact, antibiotics are successful in treating most patients.

It is always wise to start antibiotic therapy as early as possible. Your doctor may decide to use an antibiotic even without waiting for confirmation from the urine or blood test.

The routinely used tests include a blood test, a urine analysis, and a test to detect the bacteria in respiratory secretions. Most importantly, your doctor may confirm the diagnosis even when one of these tests is negative.

If you have severe dehydration or breathing problems, hospitalization may be necessary.

Serious Complications of Legionnaires’ disease You Should Not Miss

Untreated illness or a delay in seeking treatment can lead to a number of potentially fatal complications. These include:

Respiratory failure

Respiratory failure occurs when the lungs fail to provide enough oxygen to the tissues and remove carbon dioxide from the body.

Legionella pneumophila stimulates the affected person’s immune system. The immune cells release chemicals that promote inflammation. Consequently, the tiny air sacs in the lungs become inflamed and filled with fluids. This causes a severe deprivation of oxygen in the organs. A delay in the treatment at this stage can cause the lungs to stop working.

Kidney failure

Severe illness can damage tissues in the kidneys. This can lead to dangerously high levels of waste products in the bloodstream.

Septic shock

It is a life-threatening condition that results due to a sudden dangerous drop in the blood pressure. It can cause an insufficient blood supply to the vital organs. If left untreated, it can lead to failure of two or more organ systems in the body, and even death.

Legionnaires’ disease Prevention: What You Can Do

A vaccine to prevent Legionnaires’ disease is not currently available. Moreover, you cannot prevent the illness by taking antibiotics prior to an infection. However, this does not mean preventing the illness is not possible.

Below are some highly effective ways to prevent it.

  • Clean and decontaminate water systems and spas.
  • Regularly drain water from pools and hot tubs to reduce the risk of bacterial growth.
  • Maintain a temperature above 140°F in hot water systems and below 68°F in cold water systems.

Click here to learn the elements, principles, building factors, and resources of effective water management systems.

  • If you do not use hot water taps daily, make sure to flush them once them a week. How to flush? Simply, let the water flow for at least 15 seconds.
  • Use only sterile water in the nebulizer and humidifier. Wash them regularly and air dry after washing each component
  • If you have a spa pool at your home, regularly clean it using commercially available disinfectants.
  • Keep your spa baths dry when not in use.
  • If you smoke, consider quitting. Talk to your doctor to learn which quitting technique is appropriate for you.

Top 10 Interesting Legionnaires’ Disease Facts

  1. The 2015 Legionnaires’ disease outbreak in New York City was the largest outbreak in the city’s history. It sickened 138 people and killed 16. The states with the most legionella outbreaks were New York (11), Pennsylvania (8), Maryland (6), Florida (6), Ohio (6), and North Carolina (5).
  2. Legionnaires’ disease causes nearly 8000 to 18000 hospitalizations in the United States each year. An affected person spends approximately 10.2 days in the hospital and spends $26741 to $38363 for the treatment. This is according to a 2018 study published in the journal Current Opinion in Infectious Diseases.
  3. Out of 100 people who get ill with the legionella bacteria, 5 to 10 people will eventually die due to the illness. The death rate in untreated immunocompromised people can be as high as 40-80 percent, according to the WHO. However, prompt treatment can significantly reduce the death rate.
  4. Hospitalization due to legionella infection is on the rise in the United States. The CDC reports that the rate of reported cases of Legionnaires’ disease has grown by nearly five and a half times since 2000. One out of five hospitalized patients needs care in intensive care units (ICU).
  5. A full recovery from the illness may take several weeks or months even with appropriate antibiotic therapy.
  6. No laboratory test for Legionnaires’ disease is 100 percent sensitive. A 2018 study revealed that a urine test is likely to miss the diagnosis in up to 59 percent of the cases.
  7. The most commonly used antibiotics are levofloxacin (Levaquin), and moxifloxacin (Avelox). Besides, erythromycin, azithromycin (Zithromax), and clarithromycin (Biaxin) are also effective. If you do not respond to one antibiotic, your doctor may ask you to take an additional antibiotic.
  1. Unlike Legionnaires’ disease, Pontiac fever goes away without any specific treatment.
  2. The use of high doses of chlorine is sometimes ineffective in removing the legionella bacteria from water systems. In such cases, newer methods of disinfection can be useful. These include copper-silver ionization, super heating, and monochloramine disinfection.
  3. Legionella infection can spread through exposure to the bacteria on cruise ships, hotels, and resorts.


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