What are the other Names for this Condition? (Also known as/Synonyms)

• Legion Fever
• Legionella Pneumophila Infection
• Legionellosis

What is Legionnaires’ Disease? (Definition/Background Information)

• Legionnaires' Disease is caused by a bacterium, Legionella pneumophila. Infection by this bacterium could cause Pontiac fever, a mild illness that resolves over time on its own. Or, it could lead to inflammation of the lungs and a severe form of pneumonia, known as Legionnaires’ Disease
• Pontiac fever is a non-serious illness, resembling the flu, which resolves with time. Legionnaires’ Disease and Pontiac fever may sometimes be clubbed together and referred to as Legionellosis
• Although the bacterial infection and subsequent pneumonia could occur throughout the year, the bulk of cases are reported in the summer and early fall (autumn)
• Legionnaires' Disease predominantly spreads by inhalation of the bacteria, and not by casual contact. Advanced age, smoking habit, and compromised immunity are some known risk factors for the infection
• If Legionnaires' Disease is not treated, it could be fatal. Even with treatment, there are reports of ongoing health issues in some patients for many months following a bout of Legionnaire’s Disease

Who gets Legionnaires’ Disease? (Age and Sex Distribution)

• Legionnaires’ Disease is known to occur globally, though it is a relatively rare disease
• Although the disease can occur in individuals of all ages, those who are 50 years and older are reported to be more at risk of contracting the condition
• Both genders could be prone to the disease, although some strains of Legionella could sometimes affect one gender more than the other

What are the Risk Factors for Legionnaires’ Disease? (Predisposing Factors)

• Legionnaires’ Disease is more likely to develop in an individual if he/she:
  • Is 50 years of age or older
  • Currently smokes or had smoked in the past 
  • Is affected by a chronic lung disease, such as emphysema
  • Is affected by other conditions such as diabetes, kidney disease, liver failure, cancer, and others
  • Has a weakened immune system due to infections such as HIV/AIDS
  • Is on immunosuppressant drugs following organ transplantation
• Hospitalized patients or those in nursing homes are considered more at risk, since germs may spread easily in these environments (through large plumbing systems, physiotherapy equipment, etc.)
• Legionnaires' Disease spreads when an individual breathes in a mist of water or water vapor (small droplets of water in the air) contaminated with the bacteria. Therefore, using a hot tub/whirlpool spa that was used by infected individuals, and subsequently, not cleaned or disinfected properly could increase the risk of infection
• Traveling to an area with a recent known outbreak may increase the risk of contracting the disease
• Sometimes, there are more than one contributory factors such as: Active and past smokers and those with a pre-existing chronic lung disease have a higher risk for the infection, as are those individuals with compromised immune systems (either due to disease or drugs)

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases ones chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Legionnaires’ Disease? (Etiology)

The Gram-negative bacterium, Legionella pneumophila, causes most cases of Legionnaires’ Disease. The causative bacterium, Legionella, is also known to cause Pontiac fever.

• This bacterium is naturally found in freshwater and multiplies rapidly in warm water
• The bacterium is also known to survive in soil as well as a number of other environments, such as cooling towers (used in large buildings), whirlpools, hot tubs, etc.
• The disease spreads through inhalation of contaminated water droplets or mist
• On rare occasions, consuming contaminated drinking water may result in infection of the airways
• Rarely, one could also get infected while gardening, after working with contaminated soil

However, Legionnaires’ Disease does not spread from one individual to another through direct contact.

What are the Signs and Symptoms of Legionnaires’ Disease?

The symptoms of Legionnaires' Disease generally become apparent in 2-10 days after being exposed to the bacterium. If milder Pontiac fever is observed or the individual is in the early stages of Legionnaires’ Disease, the symptoms could then include:

• High fever, chills
• Headaches
• Body pain

Pontiac fever is reported to resolve on its own within a week or so. However, if an individual has Legionnaires’ Disease, the infection spreads to the lungs and could cause:

• Labored breathing
• Cough (sometimes productive)
• Chest pain
• Nausea, vomiting
• Diarrhea
• Delirium, disorientation, and confusion

Legionnaire Disease is a lung disease. However, the bacterium could potentially infect open wounds. Additionally, the infection from the lungs could spread to other parts of the body, such as the heart, kidneys, and brain.

How is Legionnaires’ Disease Diagnosed?

Legionnaires' Disease causes pneumonia. Since organisms other than Legionella could cause pneumonia, a healthcare provider is likely to use one or more of the following methods to diagnose or rule out Legionnaire’s Disease:

• A physical examination and evaluation of medical history
• An assessment of symptoms
• Chest X-ray to confirm pneumonia
• Sputum test
• Blood test
• Urine test, to check for the presence of Legionella bacteria (known as urinary antigen test)
• Lung biopsy 
• Culture of bacterial from the sputum or lung biopsy specimen
• Imaging studies of the brain, if there is reason to believe that the disease has spread to the brain

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Legionnaires’ Disease?

If left undiagnosed or untreated, Legionnaires' Disease could spread from the lungs to other organs, such as the kidneys, heart, and brain, and lead to serious health concerns, particularly in those individuals who have compromised immune systems owing to advanced age, diseases, or drugs. Some potential complications from the disease include:

• Lung failure: Inflamed air sacs in the lungs could fill with fluid, rendering the lungs incapable of gaseous exchange
• Acute renal failure, leading to fluid and waste build-up in the body
• Septic shock: The infection spreads to vital organs, resulting in a severe drop in blood pressure
• Weakened heart: The drop in blood pressure forces the heart to work harder to pump blood to the organs, weakening the heart muscles

Death: 1 in 10 individuals with Legionnaires’ Disease are reported to succumb to the disease owing to complications (according to the Centers for Disease Control and Prevention, USA).

How is Legionnaires’ Disease Treated?

The standard treatment upon diagnosis of Legionnaires’ Disease is with antibiotics; in many cases, hospitalization may be required.

• It is generally advises that the antibiotics treatment be started as early as possible and that the patients complete the prescribed course of medication
• The milder Pontiac fever resolves on its own, over a short period of time. Generally, no treatment is necessary

How can Legionnaires’ Disease be Prevented?

• At this time, no vaccines are available to prevent Legionnaires’ Disease from occurring
• Cleanliness is paramount to preventing the bacterial from thriving in any environment. Whirlpools, hot tubs, etc., need to be meticulously cleaned and disinfected, prior to and after use
• To decrease susceptibility to the condition, cessation of smoking is recommended

What is Prognosis of Legionnaires’ Disease? (Outcomes/Resolutions)

• With early diagnosis and prompt antibiotics treatment, most healthy individuals recover from the sickness within a few weeks. However, some symptoms might stay for a while after recovery. In such individuals, complete recovery might even take up to one year
• Individuals with compromised immune systems owing to advanced age, disease, or drugs and those who smoke, could face complications from the disease and it may involve prolonged hospitalization
• About 10% of the individuals with severe complications from Legionnaires’ Disease are known to die, per CDC

Additional and Relevant Useful Information for Legionnaires’ Disease:

• Legionnaires’ Disease is a relatively rare disease with an occurrence of less than 20,000 cases annually in the USA. Between 8,000 and 18,000 people are reportedly hospitalized annually in the U.S. However, it is believed that many infections could go unreported or untreated
• An outbreak of the disease occurred among attendees of the Philadelphia convention of the American Legion in 1976, and hence the name Legionnaires Disease 
• The disease existed before 1976. However, owing to the discovery of the causative organism, its diagnosis has improved, and therefore, the number of Legionnaires cases appears to have increased