What is Legionnaires disease

Legionnaires’ disease is an uncommon severe and sometimes life-threatening form of pneumonia, or lung inflammation caused by Legionella bacteria. Legionella bacteria is naturally found in water, especially warm water. Hot tubs that are not cleaned and disinfected enough can become contaminated with Legionella bacteria. A person can get infected with Legionella when they breathe in steam or mist from a contaminated hot tub.

Legionella can also be found in cooling towers, plumbing systems, and decorative pools or fountains.

Legionnaires’ disease (Legionellosis) can present as two types of illness: Legionnaires’ disease and Pontiac fever. The two illnesses can be diagnosed with similar tests, but are treated differently. The Legionella bacterium is named after a 1976 outbreak, during which some people who went to a Philadelphia convention of the American Legion suffered from a new type of pneumonia (lung infection) that became known as Legionnaires’ disease. A milder infection, also caused by Legionella, is called Pontiac fever. Pontiac fever symptoms are similar to a mild case of the flu. The term “legionellosis” may be used to refer to either Legionnaires’ disease or Pontiac fever.

People may be exposed to the Legionella bacteria at home, at work or in public places. It is most commonly contracted by older people, smokers and people with weakened immune systems. Each year, 8,000–18,000 people in the United States are hospitalized with Legionnaires’ disease. About 6,000 cases of Legionnaires’ disease were reported in the United States in 2015. However, because Legionnaires’ disease is likely underdiagnosed, this number may underestimate the true incidence. More illness is usually found in the summer and early fall, but it can happen any time of year. Legionnaires’ disease is usually treated successfully with antibiotics, but can sometimes be fatal.

Legionnaires disease continues to be detected, now more than ever.

There are at least 60 different species of Legionella bacteria; most are considered pathogenic, but most disease is caused by Legionella pneumophila (found in water), particularly serogroup 1 and Legionella longbeachae (found in soil). Legionella can be found in natural, freshwater environments, but generally is not present in sufficient numbers to cause disease. Legionella pneumophila bacteria can contaminate air conditioning cooling towers, whirlpool spas, shower heads and other bodies of water. Legionella longbeachae can contaminate soil or potting mix. In human-made water systems, like the premise plumbing of large buildings (consisting of water heaters, storage tanks, and pipes), cooling towers, decorative fountains, or hot tubs, Legionella can grow and be transmitted to susceptible hosts via aerosolization.

Legionella is transmitted via inhalation of aerosolized water containing the bacteria. Less commonly, Legionella can be transmitted via aspiration of drinking water. Legionella is not usually transmitted from person-to-person. However, a single episode of possible person-to-person transmission of Legionnaires’ disease has been reported ¹, ².

Because hotels, resorts, and cruise ships often use large, complex water systems and other aerosol-generating devices, travel is a risk factor for disease. This is also true for hospitals and long-term care facilities, which also host susceptible populations.

Certain groups of people are more likely to become seriously ill when infected with Legionella:

• Individuals who are 50 years of age or older
• Smokers
• People with chronic lung disease
• Individuals with weakened immune systems

It is important that you contact your doctor as soon as possible if you think that you have been exposed to Legionella bacteria.

Is legionnaires disease contagious?

Legionnaires’ disease is not spread from person to person. However, this may be possible in rare cases ³, ¹.

How do I protect myself and my family from Legionnaires disease?

Because high water temperatures make it hard to maintain the disinfectant levels needed to kill germs like Legionella, making sure that the hot tub has the right disinfectant and pH levels is essential. Here are some things you can do to determine whether a hot tub has been properly maintained:

Three Steps for Testing Hot Tub Water

• Purchase pool test strips at your local home improvement or pool supply store (be sure to check the expiration date).
• Use the test strips to check hot tub water for adequate free chlorine (2—4 parts per million [ppm]) or bromine (4—6 ppm) and pH (7.2—7.8) levels.
• If you find improper chlorine, bromine, and/or pH levels, tell the hot tub operator or owner immediately.

Four Questions to Ask Your Hot Tub Operator

• What was the most recent health inspection score for the hot tub?
• Are disinfectant and pH levels checked at least twice per day?
• Are disinfectant and pH levels checked more often when the hot tub is being used by a lot of people?
• Are the following maintenance activities performed regularly:
  • Removal of the slime or biofilm layer by scrubbing and cleaning?
  • Replacement of the hot tub water filter according to manufacturer’s recommendations?
  • Replacement of hot tub water?

Legionnaires disease history

Legionella was discovered after an outbreak in 1976 among people who went to a Philadelphia convention of the American Legion. Those who were affected suffered from a type of pneumonia (lung infection) that eventually became known as Legionnaires’ disease ⁴.

The first identified cases of Pontiac fever occurred in 1968 in Pontiac, Michigan, among people who worked at and visited the city’s health department. It wasn’t until Legionella was discovered after the 1976 outbreak in Philadelphia that public health officials were able to show that the same bacterium causes both diseases.

Legionnaires disease possible complications

Possible complications of Legionnaires’ disease include:

• Lung failure. This occurs when the lungs are no longer able to provide the body with enough oxygen or can’t remove enough carbon dioxide from the blood.
• Septic shock. This occurs when a severe, sudden drop in blood pressure reduces blood flow to vital organs, especially to the kidneys and brain. The heart tries to compensate by increasing the volume of blood pumped, but the extra workload eventually weakens the heart and reduces blood flow even further.
• Acute kidney failure. This is the sudden loss of your kidneys’ ability to perform their main function — filtering waste material from your blood. When your kidneys fail, dangerous levels of fluid and waste accumulate in your body.
• Death

About 1 out of every 10 people who get sick with Legionnaires’ disease will die due to complications from their illness ⁵. For those who get Legionnaires’ disease during a stay in a healthcare facility, about 1 out of every 4 will die.

Legionnaires disease outbreak

Legionellosis outbreaks occur when two or more people are exposed to Legionella and get sick in the same place at about the same time. People can get legionellosis when they breathe in a mist (small droplets of water in the air) that is contaminated with Legionella.

Outbreaks are commonly associated with buildings or structures that have complex water systems, like hotels and resorts, long-term care facilities, hospitals, and cruise ships. The most likely sources of infection include water used for showering, hot tubs, decorative fountains and cooling towers (parts of centralized air-conditioning systems for large buildings).

Legionellosis outbreaks can be difficult to identify, especially if people travel to a common location, are exposed to Legionella, and then return home before becoming sick. State and local health departments take the lead in investigating outbreaks and implementing control measures to remove Legionella from the water identified as the source of infection. The Centers for Disease Control and Prevention is only involved in legionellosis outbreak investigations when additional assistance is requested. State and local health departments are the best source of information for a specific outbreak.

Legionnaires disease causes

What causes legionnaires disease

Legionella is a type of bacterium found naturally in freshwater environments, like lakes and streams. It can become a health concern when it grows and spreads in human-made water systems like:

• Showers and faucets
• Cooling towers (air-conditioning units for large buildings)
• Hot tubs that aren’t drained after each use
• Decorative fountains and water features
• Hot water tanks and heaters
• Large plumbing systems

Home and car air-conditioning units do not use water to cool the air, so they are not a risk for Legionella growth.

Outdoors, legionella bacteria survive in soil and water, but rarely cause infections. Indoors, though, legionella bacteria can multiply in all kinds of water systems — hot tubs, air conditioners and mist sprayers in grocery store produce departments.

Although it’s possible to contract legionnaires’ disease from home plumbing systems, most outbreaks have occurred in large buildings, perhaps because complex systems allow the bacteria to grow and spread more easily.

In water, Legionella bacterium grows and multiplies within amoebae and ciliated protozoa, which are small one-celled organisms. In addition to providing nutrients for replicating and growing Legionella, protozoa also provide a shelter that protects Legionella bacterium from adverse environmental conditions, such as extreme temperatures and chemicals like chlorine. Human immune cells called alveolar macrophages look very similar to protozoa. When in human lungs, Legionella bacterium invades and grows within alveolar macrophages, mistaking them for their natural host and causing disease.

Rates of reported cases of Legionnaires’ disease continue to rise in the United States. More than 6,000 cases were reported in 2015. However, because Legionnaires’ disease is likely underdiagnosed, this number may underestimate true incidence.

Figure 1. How Legionella Affects Building Water Systems

How do you get Legionnaires disease

After Legionella grows and multiplies in a building water system, that contaminated water then has to spread in droplets small enough for people to breathe in. People can get Legionnaires’ disease when they breathe in small droplets of water in the air that contain the bacteria. This might be the spray from a shower, faucet or whirlpool, or water dispersed through the ventilation system in a large building.

Less commonly, people can get Legionnaires’ disease by aspiration of drinking water. This happens when water “goes down the wrong pipe,” into the trachea (windpipe) and lungs instead of the digestive tract. People at increased risk of aspiration include those with swallowing difficulties.

In general, people do not spread Legionnaires’ disease and Pontiac fever to other people. However, this may be possible in rare cases ³.

Legionnaires disease outbreaks have been linked to a range of sources, including:

• Hot tubs and whirlpools on cruise ships
• Grocery store mist machines
• Cooling towers in air conditioning systems
• Decorative fountains
• Swimming pools
• Physical therapy equipment
• Water systems in hotels, hospitals and nursing homes

Although legionella bacteria primarily spread through aerosolized water droplets, the infection can be transmitted in other ways, including:

Aspiration. This occurs when liquids accidentally enter your lungs, usually because you cough or choke while drinking. If you aspirate water containing legionella bacteria, you may develop legionnaires’ disease.
Soil. A few people have contracted legionnaires’ disease after working in the garden or using contaminated potting soil.

Talk to your doctor or local health department if:

• You believe you were exposed to Legionella
  AND
• You develop symptoms, such as fever, cough, chills, or muscle aches

Your local health department can determine whether or not to investigate. Be sure to mention if you spent any nights away from home in the last 10 days.

Risk factors for legionnaires disease

Most healthy people exposed to Legionella do not get sick. People at increased risk of getting sick are:

• People 50 years or older
• Current or former smokers. Smoking damages the lungs, making you more susceptible to all types of lung infections.
• People with a chronic lung disease (like chronic obstructive pulmonary disease [COPD] or emphysema)
• People with weak immune systems (e.g., HIV/AIDS) or who take drugs that weaken the immune system (like after a transplant operation or chemotherapy)
• People with cancer
• People with underlying illnesses such as diabetes, kidney failure, or liver failure
• Recent travel with an overnight stay outside of the home, including stay in a healthcare facility
• Exposure to hot tubs

Legionnaires disease prevention

There are no vaccines that can prevent legionellosis. Avoiding smoking is the single most important thing you can do to lower your risk of infection. Smoking increases the chances that you’ll develop legionnaires’ disease if you’re exposed to legionella bacteria.

The key to preventing legionellosis is making sure that the water systems in buildings are maintained in order to reduce the risk of growing and spreading Legionella. Examples of water systems that might spread Legionella include

• Hot tubs
• Hot water tanks and heaters
• Large plumbing systems
• Cooling towers (air-conditioning systems for large buildings)
• Decorative fountains

Legionella and Hot Tubs

Legionella grows best in warm water, like the water temperatures used in hot tubs. However, warm temperatures also make it hard to keep disinfectants, such as chlorine, at the levels needed to kill germs like Legionella. Disinfectant and other chemical levels in hot tubs should be checked regularly and hot tubs should be cleaned as recommended by the manufacturer. Learn how you can test the water before you use a hot tub and questions you should ask your hot tub operator to determine whether or not a hot tub has been properly maintained.

Legionnaires disease symptoms

People who get sick after being exposed to Legionella can develop two different illnesses: Legionnaires’ disease and Pontiac fever.

Table 1. Summarizes key clinical differences between Legionnaires’ disease and Pontiac fever

	Legionnaires’ disease	Pontiac fever
Clinical features	Fever, myalgia (body aches), and cough are included in the CSTE case definition. These symptoms are typical but may not always be present in all patients and are considered optional for meeting the CSTE case definition. Additional symptoms may be present, such as shortness of breath, headache, confusion, nausea, or diarrhea.	A milder illness without pneumonia is included in the CSTE case definition, often a flu-like illness (fever, chills, myalgia, malaise).
Pneumonia (clinical or radiographic)	Yes	No
Pathogenesis	Replication of organism	Possibly an inflammatory response to endotoxin
Incubation period	2 to 10* days after exposure	24 to 72 hours after exposure
Percent of persons who become ill, when exposed to the source of an outbreak	Less than 5%	Greater than 90%
Treatment	Antibiotics	Supportive care (self-resolving)
Isolation of organism	Possible	Never possible
Outcome	Hospitalization common Case-fatality rate: 10%, (25% for healthcare-associated)	Hospitalization uncommon Case-fatality rate: 0%

* The incubation period for Legionnaires’ disease is most commonly 2 to 10 days from the time of exposure to symptom onset, with an average of 5 to 6 days but has been reported to be up to 19 days in rare cases. For routine surveillance purposes, exposure histories are collected for the 10 days prior to onset. However, in outbreak settings where it is important to consider a wide range of possible sources, use of a 14-day incubation period is often desirable.

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Legionnaires’ Disease

Legionnaires’ disease usually develops 2 to 10 days after exposure to legionella bacteria, but it can take longer so people should watch for symptoms for about 2 weeks after exposure. Legionnaires’ disease is very similar to other types of pneumonia (lung infection), it frequently begins with the following signs and symptoms:

• Cough
• Shortness of breath
• Fever that may be 104 °F (40 °C) or higher
• Muscle aches
• Headaches

By the second or third day, you’ll develop other signs and symptoms that may include:

• Cough, which may bring up mucus and sometimes blood
• Shortness of breath
• Chest pain
• Gastrointestinal symptoms, such as nausea, vomiting and diarrhea
• Confusion or other mental changes

Although legionnaires’ disease primarily affects the lungs, it occasionally can cause infections in wounds and in other parts of the body, including the heart.

If you develop pneumonia symptoms, see a doctor right away. Be sure to mention if you may have been exposed to Legionella, have used a hot tub, spent any nights away from home, or stayed in a hospital in the last two weeks.

Pontiac Fever

Pontiac fever symptoms are primarily fever and muscle aches; it is a milder infection than Legionnaires’ disease. Symptoms begin between a few hours to 3 days after being exposed to the bacteria and usually last less than a week. Pontiac fever is different from Legionnaires’ disease because someone with Pontiac fever does not have pneumonia.

Legionnaires disease diagnosis

Legionellosis can present as two types of illness: Legionnaires’ disease and Pontiac fever. The two illnesses can be diagnosed with similar tests, but are treated differently.

Legionnaires’ Disease Diagnosis

Legionnaires’ disease is similar to other types of pneumonia. People with Legionnaires’ disease have pneumonia (lung infection), which can be confirmed by chest x-ray.

To help identify the presence of legionella bacteria quickly, your doctor may use a test that checks your urine for legionella antigens — foreign substances that trigger an immune system response.

You may also have one or more of the following:

Clinicians typically use two preferred types of tests to see if a patient’s pneumonia is caused by Legionella:

• Blood tests
• Chest X-ray, which doesn’t confirm legionnaires’ disease but can show the extent of infection in your lungs
• Laboratory test that involves taking a sample of sputum (phlegm) or washing from the lung
• A CT scan of your brain or a spinal tap (lumbar puncture) if you have neurological symptoms such as confusion or trouble concentrating

Urinary Antigen Test

The most commonly used laboratory test for diagnosis of legionellosis is the urinary antigen test, which detects a molecule of the Legionella bacterium in urine. If the patient has pneumonia and the test is positive, then the patient is considered to have Legionnaires’ disease. The test can remain positive for a few weeks after infection, even with antibiotic treatment. The urinary antigen test detects the most common cause of legionellosis, Legionella pneumophila serogroup 1. However, all species and serogroups of legionellae are potentially pathogenic, so a patient with a negative urinary antigen result could have legionellosis caused by other Legionella species and serogroups.

Sputum (phlegm) or Washing from the Lung Culture

Isolation of Legionella on selective media (i.e., Buffered Charcoal Yeast Extract [BYCE] agar) from lower respiratory secretions, lung tissue, pleural fluid, or a normally sterile site is confirmatory and an important method for diagnosis. In addition, if urinary antigen testing is negative but Legionnaires’ disease is still suspected, a respiratory culture should be conducted to look for other Legionella species and serogroups that the urinary antigen test does not detect.

Comparing clinical and environmental isolates using serological and molecular techniques can help identify the source in Legionnaires’ disease outbreak investigations. Because Legionella is commonly found in the environment, clinical isolates can help interpret the findings of an environmental investigation.

Sensitivity and Specificity of Diagnostic Tests

Sensitivity varies depending on the quality and timing of clinical specimen collection, as well as technical skill of the laboratory worker performing the test. The table below provides general ranges for the sensitivity and specificity of each diagnostic test.

Table 2. Sensitivity and specificity of each diagnostic test

Test	Sensitivity (%)	Specificity (%)
Culture	20–80	100
Urinary antigen for L. pneumophila serogroup 1* (Lp1)	70–100	95–100
Paired serology**	80–90	>99
Direct Fluorescent Antibody (DFA) Stain	25–75	≥95
Polymerase Chain Reaction (PCR)	unknown	unknown

*Cross reactions with other species and serogroups have been documented.

**Centers for Disease Control and Prevention labs do not perform serology testing for legionellosis diagnosis due to inherent limitations of this approach.

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Table 3. Advantages and Disadvantages for Each Diagnostic Test

Test	Advantages	Disadvantages
Culture	Detects all species and serogroups Clinical and environmental isolates can be compared	Technically difficult Slow (>5 days to grow) Sensitivity highly dependent on technical skill Affected by appropriate antibiotic treatment Requires BCYE agar, which some laboratories may not have readily available
Urinary Antigen	Rapid (same day)	Can only be used to identify L. pneumophila serogroup 1* (Lp1) [which may account for up to 80% of cases] Does not allow for molecular comparison to environmental isolates
Serology**	Possible to detect species and serogroups other than Lp1	Must have paired sera collected at acute onset to 2 weeks after symptoms and 3 to 6 weeks later Approximately 5 to 10% of the population has titer 1:≥256 (single acute phase antibody titers of 1: ≥256 do not discriminate between cases of Legionnaires’ disease and other causes of community-acquired pneumonia)
DFA	Can be performed on pathologic specimens (usually lung tissue) Possible to detect species and serogroups other than Lp1	Technically difficult
PCR	Can be performed on pathologic specimens (usually lung tissue) Rapid Possible to detect species and serogroups other than Lp1	Assays vary by laboratory and are not FDA-approved

*Cross reactions with other species and serogroups have been documented.

**Centers for Disease Control and Prevention labs do not perform serology testing for legionellosis diagnosis due to inherent limitations of this approach.

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Pontiac Fever Diagnosis

Clinicians can use a urine or blood test to see if someone has Pontiac fever. However, a negative test doesn’t rule out that someone may have it (this is called a false negative). Clinicians most often diagnose Pontiac fever when there are other known laboratory-confirmed legionellosis cases (either Legionnaires’ disease or Pontiac fever) who may have been exposed to Legionella at the same time or place.

Legionnaires disease treatment

Legionnaires’ disease is treated with antibiotics. The sooner therapy is started, the less likely the chance of serious complications or death. In many cases, treatment requires hospitalization. Pontiac fever goes away on its own without treatment and causes no lingering problems.

References

1. Borges V, Nunes A, Gomes B, Capucho R, et al. Probable person-to-person transmission of Legionnaires’ disease. N Eng J Med. 2016;374:497–81.
2. Correia AM, GonCalves J, Gomes, JP, et al. Probable person-to-person transmission of Legionnaires’ disease. N Engl J Med. 2016;374:497–8.
3. Correia AM, GonCalves J, Gomes, JP, et al. Probable Person-to-Person Transmission of Legionnaires’ Disease. N Engl J Med. 2016;374:497–8. http://www.nejm.org/doi/full/10.1056/NEJMc1505356
4. Magazine story covers related to the 1976 outbreak of Legionnaire’s disease. From Centers for Disease Control and Prevention (CDC) Public Health Library, #1185. Copyright 1976 by CDC. Reprinted with permission.
5. Dooling KL, Toews KA, Hicks LA, et al. Active Bacterial Core Surveillance for Legionellosis–United States, 2011–2013. MMWR Morb Mortal Wkly Rep. 2015;64(42):1190–3
6. Legionella (Legionnaires’ Disease and Pontiac Fever). https://www.cdc.gov/legionella/clinicians/clinical-features.html
7. Legionella (Legionnaires’ Disease and Pontiac Fever) Diagnosis, Treatment, and Prevention. https://www.cdc.gov/legionella/clinicians/diagnostic-testing.html