What is Legionella?
Legionella was identified as the cause of the July 1976 outbreak of pneumonia among
people at a convention of the American Legion in Philadelphia. Accordingly, this
previously unknown bacteria and the disease it caused, Legionnaires’ disease, were
are characterized as gram-negative, aerobic, unencapsulated bacil i. Fifty bacterial species with more than 70 serogroups make up this genus; 20 of the species are known to be associated with human infection.
What is Legionnaires’ disease?
Legionnaires’ disease, or Legionel osis, is a severe infection caused by Legionella
primarily L. pneumophila
, which is responsible for 90% of infections. The disease
typical y presents as pneumonia and symptoms may include a high fever, chil s, cough,
muscle aches, headaches, and diarrhea.
Pontiac fever is an acute, febrile, self-limited il ness that has been linked to Legionella
species. This infection is general y characterized by fever, fatigue, and muscle pain.
Antimicrobial treatment does not need to be administered to treat this infection, but should
be prescribed for cases of Legionnaires’ disease.
What are the most common species that cause human infection?
Most reported cases of Legionnaires’ disease are caused by Legionella pneumophila
serogroup 1. The estimated proportion of cases caused by species is: • L. pneumophila
(91.4%)• L. micdadei
(2.8%)• L. longbeachae
(2.2%)• L. dumoffii
(1.5%)• L. bozemanii
Where is Legionella found?
• Environmental water sources
• Potable water, such as that from faucets, showers, and hot water tanks
• Cooling towers and hot tubs
Who is at risk of Legionella infection?
infection can occur in a variety of hosts. The incidence of Legionnaires’ disease
depends on the degree of water contamination, the intensity of the patient’s exposure to
that water, and the susceptibility of the patient. The presence of the bacteria in the
aforementioned sources does not in and of itself constitute a dangerous condition or
disease threat to healthy individuals. Legionella
in a hospital water system increases the risk
of hospital acquired infection for:
• Immuno-compromised and those with underlying diseases
• Transplant patients are at risk for infection
• Cigarette smoking, chronic lung disease, and immunosuppressive treatment
How is Legionella transmitted?
• Aspiration of water contaminated with the organism
• Contaminated respiratory-therapy equipment
• Inhalation of aerosols containing Legionella
What are the clinical manifestations of infection?
Symptoms of infection may develop after a few days or up to two weeks after exposure to
the bacterium. Pneumonia is the major clinical presentation of Legionella
typical y caused by aspiration or aerosolization of water from a contaminated water
source. The persistence of pulmonary infiltrates is suggestive of Legionnaires’ disease.
Other symptoms include fever, headache, confusion, and muscle pain. Some advanced
disease symptoms may include gastrointestinal and nervous system problems.
How is Legionella infection diagnosed?
• Culture of the bacteria on selective media
• Detection of Legionella-
specific antibodies in serum (serology)
• It is necessary to conduct antibody testing of both acute- and convalescent-phase sera
when diagnosing Legionnaires’ disease.
What treatment is available?
There is currently no vaccine available for the disease. Antimicrobial agents such as
macrolides and quinolones are effective in treating Legionella
infections, which include:
How can Legionella be monitored and controlled in water supplies?
There are several short term and long term water treatment options to reduce Legionel a
bacteria in water systems. These include chemical treatment or repeated thermal
eradication. If il ness is suspected to be from Legionella
in a contaminated water source,
the water should be immediately tested. Additional y, experts should be consulted for
guidance regarding treatment of the water system.
• The role of environmental surveil ance in determining risk for hospital-acquired
Legionel osis: a national surveil ance study with clinical correlations. Stout JE, Muder RR, Mietzner S, Wagener MM, et al. Infect Control Hosp. Epidemiol.
• Community-acquired Legionnaires’ disease: Implications for under diagnosis and
laboratory testing. Yu VL, Stout JE. Clin Infect Dis.
Disclaimer: This information is provided for informational purposes only and not for the purpose of providing legal or medical advice. You should contact your physician or attorney to obtain advice with respect to any particular issue or problem.
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