Disease: Legionnaires' Disease and Pontiac Fever (Legionellosis)

    Legionnaires' disease and Pontiac fever (legionellosis) facts

    • Legionellosis is an infection that is caused by a bacterium.
    • The bacterium thrives in the mist that is sprayed from air-conditioning ducts.
    • The bacterium can infest an entire building.
    • The illness takes two distinct forms: Legionnaires' disease and Pontiac fever.
    • Legionnaires' disease is the more severe form and can be fatal.
    • Pontiac fever is the far milder form of the illness.
    • Symptoms of Legionnaires' disease include fever, chills, and a cough.
    • At its worst, Legionnaires' disease can cause severe pneumonia and respiratory failure.
    • Although antibiotics are effective for treatment, the most useful approach is prevention.

    What causes legionellosis? What is the history of Legionnaires' disease?

    Legionellosis is an infection that is caused by the bacterium Legionella pneumophila. The disease has two distinct forms:

    • Legionnaires' disease is the more severe form of the infection, which may involve pneumonia. The onset of this form of the disease is usually two to 10 days after infection but can occur up to 16 days later. Legionnaires' disease acquired its name in 1976 after an outbreak of pneumonia occurred among people attending a convention of the American Legion in Philadelphia. Later, the bacterium causing the illness was named Legionella pneumophila.
    • Pontiac fever is a milder illness that develops from hours to two days after initial infection and resolves spontaneously.
    X-ray image of lungs of patient with Legionnaires' disease; SOURCE: CDC

    How common is Legionnaires' disease?

    Legionnaires' pneumonia is not uncommon. In fact, it represents over 4% of all community-acquired pneumonias. An additional unknown number of people are infected with the Legionella bacterium but have only mild symptoms or no symptoms at all (so-called Pontiac fever).

    Outbreaks of Legionnaires' disease have received the most media attention. A recent outbreak was associated with a party at the Playboy mansion in Los Angeles where at least four individuals contracted Legionnaires' disease. However, the disease most often occurs as single, isolated cases not associated with any identified outbreak. Outbreaks are usually recognized in the summer and early fall, but cases may occur year-round.

    Since the bacterium of Legionnaires' disease was identified in 1976, numerous hospital-acquired outbreaks of the disease have also been reported. These outbreaks have enabled researchers to study epidemics of legionellosis.

    What are the usual symptoms of Legionnaires' disease?

    Patients with Legionnaires' disease usually develop a fever, chills, and a cough. The cough may either be dry or produce sputum. Some patients with Legionnaires' disease also have muscle aches, headache, tiredness, loss of appetite, and occasionally diarrhea. Legionnaires' disease can cause a severe pneumonia, seriously affect breathing, even lead to respiratory failure and adult respiratory distress syndrome (ARDS). In some cases, the heart rate is slower than expected for the degree of fever. There are no specific symptoms that directly identify Legionnaires' pneumonia. Legionnaires' pneumonia presents in a manner similar to Chlamydia pneumonia and Mycoplasma pneumonia, so-called atypical pneumonias (previously referred to as "walking pneumonia"). These are referred to as atypical because, unlike typical pneumonia (as characterized by Streptococcus pneumonia), which involves high, spiking fevers, sudden onset, cough, and purulent sputum and often chest pain and a localized infiltrate on chest X-ray.

    People with Pontiac fever experience a self-limiting influenza-like illness with fever, chills, headache, and muscle aches but, by definition, do not have pneumonia. Affected individuals generally recover in two to five days without treatment.

    How is the diagnosis of Legionnaires' disease made?

    Laboratory tests may include a modest increase in white blood cells, mild abnormalities in liver function studies, a low sodium in the blood, and even some decreased function of the kidneys. Nevertheless, these features can also be seen with a variety of different types of pneumonia. Chest X-rays often demonstrate abnormal densities (areas of that lungs that on the X-ray film appear whiter). However, it is difficult to distinguish Legionnaires' disease from other types of pneumonia by symptoms and chest X-ray alone. Additional specific tests are required for diagnosis.

    These other tests are specialized and are not routinely performed on people with fever or pneumonia. Several types of tests are available. The most useful test uses a urine sample to detect identifiable proteins of the Legionnaires' bacterium (Legionella antigens). This test has the disadvantage of only testing for Legionella pneumophila serogroup 1 (this is the organism responsible for most of the cases). Additionally, detecting the bacteria in a culture of the sputum may be helpful. Lastly, tests that compare antibody levels of Legionella in two blood samples obtained three to six weeks apart showing a fourfold rise in the antibodies in the blood against the bacterium can be confirmatory after the disease is gone.

    Because these tests complement each other, a positive result from each test when Legionnaires' disease is suspected increases the probability of confirming the diagnosis. However, because none of the laboratory tests is 100% sensitive, the diagnosis of legionellosis is not excluded even if one or more of the tests is negative. Of the available tests, the most specific is culture isolation of the bacterium from secretions from the respiratory tract.

    Who develops Legionnaires' disease?

    People of any age can develop Legionnaires' disease, but the illness most often affects middle-aged and older people, particularly those who smoke cigarettes or have chronic lung disease, as these individuals have a greater likelihood of developing any respiratory illness.

    People at an increased risk for Legionnaires' disease also include people whose immune systems are suppressed by diseases such as cancer, kidney failure requiring dialysis, diabetes, or AIDS. Those who take medications that suppress the immune system are also at risk including those chronically on steroids.

    Pontiac fever most commonly occurs in people who are otherwise healthy.

    What is the treatment for Legionnaires' disease?

    There are three major classes of antibiotics that are effective in treating legionellosis. These include the fluoroquinolones such as levofloxacin (Levaquin), and moxifloxacin (Avelox), the macrolides such as erythromycin, azithromyocin (Zithromax), and clarithromycin (Biaxin), and the tetracyclines including doxycycline (Vibramycin). A new class of antibiotics (glycylcyclines) are also effective. The choice of antibiotic is often dependent on the patient's clinical state, tolerance to the medication, and degree of certainty as to the diagnosis. Zithromax and Levaquin are particularly effective because of decreased gastrointestinal irritation, higher potency, better penetration into tissue, and once-daily dosing.

    Learn more about: Cipro | Levaquin | Avelox | Zithromax | Biaxin | Vibramycin

    In severe cases of Legionnaires' disease that seem more resistant to a single antibiotic, a second drug called rifampin (Rifadin) may be added.

    Pontiac fever requires no specific treatment.

    How is Legionnaires' disease spread?

    Outbreaks of legionellosis have occurred after people have inhaled aerosols that come from a water source (for example, air-conditioning cooling towers, whirlpool spas, or showers) contaminated with Legionella bacteria. People may be exposed to these aerosols in homes, workplaces, hospitals, or public places. Infection cannot be acquired from another person with legionellosis, and there is no evidence of people becoming infected from auto air conditioners or household window air-conditioning units.

    Cases of Legionnaires' disease have increased throughout the United States, but this most likely represents increased detection by better diagnostic tests. Some would suggest that this increase may be due to global warming, though this seems unlikely.

    Hospital-acquired infections have occurred and are usually due to contamination of the water supply. Two well-reported cases occurred in the 1980s in Los Angeles, one at the Wadsworth VA hospital and the other at the City of Hope. Guidelines have now been established for routine environmental testing for Legionnaires' in several states in the United States and by the Veterans Affairs health-care system.

    With regard to travel-associated infection, this usually occurs in hotels from contaminated water, most notably at the Legionnaires' convention in Philadelphia. This disease has also been associated with travel on cruise ships.

    Some data suggest an increase incidence of Legionnaires' in the elderly in nursing homes linked to eating puréed food, probably also due to increased aspiration in this population.

    How common is Legionnaires' disease?

    Legionnaires' pneumonia is not uncommon. In fact, it represents over 4% of all community-acquired pneumonias. An additional unknown number of people are infected with the Legionella bacterium but have only mild symptoms or no symptoms at all (so-called Pontiac fever).

    Outbreaks of Legionnaires' disease have received the most media attention. A recent outbreak was associated with a party at the Playboy mansion in Los Angeles where at least four individuals contracted Legionnaires' disease. However, the disease most often occurs as single, isolated cases not associated with any identified outbreak. Outbreaks are usually recognized in the summer and early fall, but cases may occur year-round.

    Since the bacterium of Legionnaires' disease was identified in 1976, numerous hospital-acquired outbreaks of the disease have also been reported. These outbreaks have enabled researchers to study epidemics of legionellosis.

    What are the usual symptoms of Legionnaires' disease?

    Patients with Legionnaires' disease usually develop a fever, chills, and a cough. The cough may either be dry or produce sputum. Some patients with Legionnaires' disease also have muscle aches, headache, tiredness, loss of appetite, and occasionally diarrhea. Legionnaires' disease can cause a severe pneumonia, seriously affect breathing, even lead to respiratory failure and adult respiratory distress syndrome (ARDS). In some cases, the heart rate is slower than expected for the degree of fever. There are no specific symptoms that directly identify Legionnaires' pneumonia. Legionnaires' pneumonia presents in a manner similar to Chlamydia pneumonia and Mycoplasma pneumonia, so-called atypical pneumonias (previously referred to as "walking pneumonia"). These are referred to as atypical because, unlike typical pneumonia (as characterized by Streptococcus pneumonia), which involves high, spiking fevers, sudden onset, cough, and purulent sputum and often chest pain and a localized infiltrate on chest X-ray.

    People with Pontiac fever experience a self-limiting influenza-like illness with fever, chills, headache, and muscle aches but, by definition, do not have pneumonia. Affected individuals generally recover in two to five days without treatment.

    How is the diagnosis of Legionnaires' disease made?

    Laboratory tests may include a modest increase in white blood cells, mild abnormalities in liver function studies, a low sodium in the blood, and even some decreased function of the kidneys. Nevertheless, these features can also be seen with a variety of different types of pneumonia. Chest X-rays often demonstrate abnormal densities (areas of that lungs that on the X-ray film appear whiter). However, it is difficult to distinguish Legionnaires' disease from other types of pneumonia by symptoms and chest X-ray alone. Additional specific tests are required for diagnosis.

    These other tests are specialized and are not routinely performed on people with fever or pneumonia. Several types of tests are available. The most useful test uses a urine sample to detect identifiable proteins of the Legionnaires' bacterium (Legionella antigens). This test has the disadvantage of only testing for Legionella pneumophila serogroup 1 (this is the organism responsible for most of the cases). Additionally, detecting the bacteria in a culture of the sputum may be helpful. Lastly, tests that compare antibody levels of Legionella in two blood samples obtained three to six weeks apart showing a fourfold rise in the antibodies in the blood against the bacterium can be confirmatory after the disease is gone.

    Because these tests complement each other, a positive result from each test when Legionnaires' disease is suspected increases the probability of confirming the diagnosis. However, because none of the laboratory tests is 100% sensitive, the diagnosis of legionellosis is not excluded even if one or more of the tests is negative. Of the available tests, the most specific is culture isolation of the bacterium from secretions from the respiratory tract.

    Who develops Legionnaires' disease?

    People of any age can develop Legionnaires' disease, but the illness most often affects middle-aged and older people, particularly those who smoke cigarettes or have chronic lung disease, as these individuals have a greater likelihood of developing any respiratory illness.

    People at an increased risk for Legionnaires' disease also include people whose immune systems are suppressed by diseases such as cancer, kidney failure requiring dialysis, diabetes, or AIDS. Those who take medications that suppress the immune system are also at risk including those chronically on steroids.

    Pontiac fever most commonly occurs in people who are otherwise healthy.

    What is the treatment for Legionnaires' disease?

    There are three major classes of antibiotics that are effective in treating legionellosis. These include the fluoroquinolones such as levofloxacin (Levaquin), and moxifloxacin (Avelox), the macrolides such as erythromycin, azithromyocin (Zithromax), and clarithromycin (Biaxin), and the tetracyclines including doxycycline (Vibramycin). A new class of antibiotics (glycylcyclines) are also effective. The choice of antibiotic is often dependent on the patient's clinical state, tolerance to the medication, and degree of certainty as to the diagnosis. Zithromax and Levaquin are particularly effective because of decreased gastrointestinal irritation, higher potency, better penetration into tissue, and once-daily dosing.

    Learn more about: Cipro | Levaquin | Avelox | Zithromax | Biaxin | Vibramycin

    In severe cases of Legionnaires' disease that seem more resistant to a single antibiotic, a second drug called rifampin (Rifadin) may be added.

    Pontiac fever requires no specific treatment.

    How is Legionnaires' disease spread?

    Outbreaks of legionellosis have occurred after people have inhaled aerosols that come from a water source (for example, air-conditioning cooling towers, whirlpool spas, or showers) contaminated with Legionella bacteria. People may be exposed to these aerosols in homes, workplaces, hospitals, or public places. Infection cannot be acquired from another person with legionellosis, and there is no evidence of people becoming infected from auto air conditioners or household window air-conditioning units.

    Cases of Legionnaires' disease have increased throughout the United States, but this most likely represents increased detection by better diagnostic tests. Some would suggest that this increase may be due to global warming, though this seems unlikely.

    Hospital-acquired infections have occurred and are usually due to contamination of the water supply. Two well-reported cases occurred in the 1980s in Los Angeles, one at the Wadsworth VA hospital and the other at the City of Hope. Guidelines have now been established for routine environmental testing for Legionnaires' in several states in the United States and by the Veterans Affairs health-care system.

    With regard to travel-associated infection, this usually occurs in hotels from contaminated water, most notably at the Legionnaires' convention in Philadelphia. This disease has also been associated with travel on cruise ships.

    Some data suggest an increase incidence of Legionnaires' in the elderly in nursing homes linked to eating puréed food, probably also due to increased aspiration in this population.

    Source: http://www.rxlist.com

    Laboratory tests may include a modest increase in white blood cells, mild abnormalities in liver function studies, a low sodium in the blood, and even some decreased function of the kidneys. Nevertheless, these features can also be seen with a variety of different types of pneumonia. Chest X-rays often demonstrate abnormal densities (areas of that lungs that on the X-ray film appear whiter). However, it is difficult to distinguish Legionnaires' disease from other types of pneumonia by symptoms and chest X-ray alone. Additional specific tests are required for diagnosis.

    These other tests are specialized and are not routinely performed on people with fever or pneumonia. Several types of tests are available. The most useful test uses a urine sample to detect identifiable proteins of the Legionnaires' bacterium (Legionella antigens). This test has the disadvantage of only testing for Legionella pneumophila serogroup 1 (this is the organism responsible for most of the cases). Additionally, detecting the bacteria in a culture of the sputum may be helpful. Lastly, tests that compare antibody levels of Legionella in two blood samples obtained three to six weeks apart showing a fourfold rise in the antibodies in the blood against the bacterium can be confirmatory after the disease is gone.

    Because these tests complement each other, a positive result from each test when Legionnaires' disease is suspected increases the probability of confirming the diagnosis. However, because none of the laboratory tests is 100% sensitive, the diagnosis of legionellosis is not excluded even if one or more of the tests is negative. Of the available tests, the most specific is culture isolation of the bacterium from secretions from the respiratory tract.

    Source: http://www.rxlist.com

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