Medical Articles

Title: Legionellosis
Date: 07-Oct-2012
Source/Author: By Datuk Dr M Jegathesan Clinical Consultant (Microbiology), Amutha Muniandy Head of Department (Microbiology), Suguna Rasamanikam Second in charge (Microbiology)

By Datuk Dr M Jegathesan    Clinical Consultant (Microbiology)
     Amutha Muniandy                Head of Department (Microbiology)
     Suguna Rasamanikam          Second in charge (Microbiology)

Legionellosis is a disease characterized by an often fatal pneumonia affecting groups of generally elderly and immunocompromised patients who are exposed to a common source such as the cooling towers of air conditioning systems in hospitals and hotels. One way to prevent such an occurrence is to monitor regularly such cooling towers.

Legionellosis is caused by bacteria found in water sources in the environment. People get legionellosis when they inhale water mist containing the bacteria called Legionella.

What is legionellosis?
Legionellosis is a lung infection that is caused by the inhalation of water aerosols containing Legionella bacteria into the lungs. It can be mild or severe enough to cause death. The more severe form of infection is called Legionnaire's disease. This is a potentially fatal pneumonia. In its mild form, it is called Pontiac fever, an often undiagnosed and generally self limiting upper respiratory infection.

What are Legionella?
Legionella are aerobic, non spore forming, typically flagellated, gram negative bacteria. There are 25 species of Legionella and 42 serogroups. Legionella pneumophila serotype 1 is the most (85%) common species isolated from infected individuals.

Where are Legionella found?
The natural habitats of Legionella species include waters worldwide and are associated almost exclusively with surface and potable waters or very moist environments. The bacteria lives best in warm, stagnant water. Legionella colonization can occur in faucets, showerheads, plumbing fixtures, hot water systems, whirlpool spas and cooling towers.

How do people get legionellosis?
People get legionellosis by the inhalation of Legionella organisms from contaminated water aerosols (water mist). Legionellosis is not contagious. People can be exposed to aerosols from mist producing devices (especially water heaters and air-conditioning systems) in homes, workplaces, hospitals, or other public places.

The primary route of Legionella infection in humans is inhalation of aerosolized bacteria. Therefore, showers, faucets, evaporative condensers, cooling towers and other aerosolizing agents are of paramount concern. It is generally agreed that monitoring of water systems is warranted in order to identify the source of an outbreak, evaluate biocides or to monitor areas where immunocompromised individuals are present (hospitals). When monitoring is not routinely performed, aggressive maintenance and disinfection procedures should be implemented. Institutions that have prevention and monitoring programs should include hospitals, health care facilities, industrial plants, hotels and old folk's homes.

Laboratory methods for diagnosis of Legionella infection and environmental screening assay
A variety of analytical methods are available for the detection of Legionella. Screening tests include Direct and Indirect Fluorescent Antibody (IFA) techniques and Polymerase Chain Reaction (PCR) techniques, although these methods may detect non viable Legionella. Antibody testing (serology) of blood sample for antibodies to Legionella. The culture method, which involves plating samples on Buffered Charcoal Yeast Extract (BCYE) agar and incubating them for up to 10 days, detects only viable organisms, and is the generally accepted standard procedure for Legionella testing. Finally, urinary antigen test, allows for early diagnosis of Legionella pneumophila serogroup 1 infection through detection of a specific soluble antigen present in the urine of patients with Legionnaires' disease.

Tests available at Gribbles Pathology Malaysia;

  1. Water samples for Legionella culture
  2. Urinary antigen test
  3. Serology testing (Total antibodies)
Test Description Specimen
1. Culture

Growing of bacterium from water samples on specialized culture media. 1 liter of water samples (eg. Hot water storage tank, cooling towers and reservoirs) collected in a plastic container. Samples should be shipped, unrefrigerated to the laboratory.
2. Urinary

Screening of urine samples for the presence of specific Legionella antigen (L. pneumophila serogroup 1) Urine samples collected in clean urine container.

Screening of blood sample for antibodies to Legionella: generally requires comparison of results from two samples, one collected during acute illness and the other 2-8 weeks Blood collected in plain tube (serum)


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