Legionnaires’ disease is a common name for one of the several illnesses caused by Legionnaires’ disease bacteria (LDB). Legionnaires’ disease is an infection of the lungs and is a form of pneumonia. More than 43 species of Legionella have been identified and more than 20 linked with human diseases.
Legionellosis is the term for the diseases produced by LDB.In addition to Legionnaires’ disease, the same bacteria also causes a flu-like disease called Pontiac fever.
What are LDB?
Legionella pneumophila Bacterium The Centers of Disease Control and Prevention (CDC) first identified Legionella pneumophila in 1977 as the cause of an outbreak of pneumonia that caused 34 deaths at a 1976 American Legion Convention in Philadelphia. L.
pneumophila had undoubtedly caused previous pneumonia outbreaks, but the organism’s slow growth and special growth requirements prevented earlier discovery.
The species of Legionella that have been associated with cases of Legionnaires’ disease are called Legionnaires’ disease bacteria (LDB).
L. pneumophila is a gram-negative rod that exists in a number of distinguishable serogroups.
Other species of Legionella cause legionellosis but L. pneumophila causes the majority of cases.
L. pneumophila is also implicated in wound infections, pericarditis, and endocarditis without the presence of pneumonia.
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.
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 symptoms?
Legionellosis is associated with two distinct illnesses: Legionnaires’ disease, which is characterized by fever, myalgia, cough, pneumonia, and Pontiac fever, a milder illness without pneumonia.
Legionnaires’ disease has an incubation period (the time from exposure to the onset of symptoms) of 2 to 10 days. Severity ranges from a mild cough and low fever to rapidly progressive pneumonia, coma, and death.
Not all individuals with Legionnaires’ disease experience the same symptoms.
Early symptoms include slight fever, headache, aching joints and muscles, lack of energy or tiredness, and loss of appetite.
Later symptoms include:
- High fever (102° to 105° F, or 39° to 41° C)
- Cough (dry at first, later producing phlegm)
- Difficulty in breathing or shortness of breath
- Chest pain
- Common gastrointestinal symptoms include vomiting, diarrhea, nausea, and abdominal pain.
- Pontiac fever is a non-pneumonia disease with a short incubation period of one to three days. Full recovery usually occurs in two to five days without medical intervention and no deaths have been reported.
- Pontiac fever produces flu-like symptoms that may include fever, headache, tiredness, loss of appetite, muscle and joint pain, chills, nausea, and a dry cough.
Pontiac fever has been associated with exposure to non-viable LDB and may be a hypersensitivity response to bacterial or other antigens rather than an infection.
What are the incidence rates and risk factors?
Legionnaires’ disease depends on the level of contamination in the water source, the susceptibility of the person exposed, and the intensity of exposure.
Unlike Legionnaires’ disease, which occurs in approximately 5 percent or less of people who are exposed, Pontiac fever will occur in approximately 90 percent of those exposed.
The factors that cause the same organism to produce two illnesses with major differences in “attack rate” (the fraction of exposed persons who become infected) and severity are not known.
In the United States, Legionnaires’ disease is fairly common and serious. LDB are one of the top three causes of non-epidemic, community-acquired pneumonia.
It is estimated that over 25,000 cases of the illness occur each year and cause more than 4,000 deaths.
The fatality rate is similar to that of other forms of pneumonia, approximately 15 percent.
It is difficult to distinguish this disease from other forms of pneumonia; so many cases go unreported.
Legionnaires’ disease is characterized as an “opportunistic” disease that attacks individuals who have an underlying illness or weakened immune system. The most susceptible people include:
The elderly, smokers, and those on immunosuppressive therapy.
Individuals with chronic obstructive pulmonary disease (COPD), organ transplant patients, and people taking corticosteroid therapy.
It is important to emphasize that relatively healthy individuals can be at risk of contracting disease.
How is Legionnaires’ disease diagnosed and treated?
caused by LDB is not easily distinguished from other forms of pneumonia.
The Centers for Disease Control and Prevention (CDC) defines a confirmed case of Legionnaires’ disease as a clinically compatible case that is confirmed by a laboratory.
A confirmed case requires a physician’s diagnosis of pneumonia based on a chest x-ray and positive laboratory test results.
A laboratory test is necessary for confirmation because the symptoms and x-ray evidence of Legionnaires’ disease resemble those of other types of pneumonia.