Legionella sp.

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Legionella sp.

• Legionnaires Disease
• Pontiac Fever

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Genus Legionella

• Best-studied species is L. pneumophila
• accounts for 85 of infections
• motile, Gram-negative, aerobic rod
• complex nutritional requirements
• 50 species in genus, gt half implicated in human
  disease
• L. micdadei mild, febrile, flu-like illness
  called Pontiac fever
• self-limiting, little or no tissue damage

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Ecology

• There are 40 species in the family of legionella
  bacteria in the world. Of these species, 12 have
  been implicated in human disease. 90 of these
  disease cases are caused by Legionella
  Pneumophila.
• There are 15 serogroups of L. Pneumophila and
  most cases are associated with serogroup 1.
  There are 5 subgroups in this serogroup which
  have different degrees of virulence.

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Ecology

• Legionella are usually found in the freshwater of
  streams, lakes, warm springs, rivers, and
  riverbanks.
• In their natural aquatic environment, legionella
  feed on various nutrients from the water, but are
  most adept in the role of an intracellular
  parasite on other bacteria.
• Once it is uptaken by a larger bacterium, it
  resists bacterial defenses and then multiplies.

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Ecology

• Environmental conditions which promote the growth
  of legionella are
• Water temperature between 20 50 ºC.
• Stagnant water.
• pH range of 2.0 8.5
• Sediment in water which supports the growth of
  supporting microbiota.
• Presence microbiota including algae, protozoa,
  and others.
• L-Cysteine-HCL and Iron salts to promote growth.

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Ecology

• The range of temperatures within which legionella
  survives and thrives

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Pathogenesis

• In their usual aquatic environment, legionella do
  not cause infections. But, when transferred to
  water supplies and air conditioning units, they
  are able to cause large outbreaks of disease.
• Legionnaires Disease is caused by inhaling L.
  pneumophila bacteria dispersed in aerosols of
  contaminated water from the environment.
• These aerosols are provided by devices in which
  warm water can stagnate, such as A/C cooling
  towers, humidifiers, shower heads, decorative
  fountains, and water misters in grocery stores.

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RISK AREAS

• Hot cold water systems
• Cooling Towers Air Conditioning
• Storage Cisterns
• Calorifiers
• Deadlegs
• Showers
• Spa pools

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SHOWERS
Operate at desired temps Poor hygiene Infrequently
used Prone to scaling Create aerosol
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DEAD LEGS
Stagnant water Ambient temps Breeding ground
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STORAGE TANKS
Over capacity Stagnation Out of site Poor
flow Ambient temps
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CALORIFIERS
Can run at critical temps Thermal
stratification Sludge build up
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COOLING TOWERS
Run at ideal temps Open to elements Contamination
via water supply Intermittent use Drift affects
wide area
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Virulence Factors

• Environmental survival
• free living
• intracellular parasites of amoebae (Acanthamoeba
  sp, Naegleria sp), ciliated protozoa, slime molds
• more resistant than free-living bacteria to
  biocides
• Biofilms
• more resistant to disinfectants (very slow growth
  rate in the biofilm)

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Virulence Factors

• Phospholipase C
• hydrolyzes phosphatidylcholine
• may injure phagocytes and lung tissue
• could allow escape from phagosome
• Protein kinases
• phosphorylate tyrosine, serine, threonine
  residues in eucaryotic signaling proteins

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Pathogenesis

• L. Pneumophila enters a human host by penetrating
  into the alveolar region of the lungs the size
  of the bacterium allows its entrance in the human
  respiratory tract.
• Alveolar macrophages attempt to ingest the
  invader. Instead of being destroyed within the
  macrophage, they grow and replicate , eventually
  killing the macrophage. Many new legionella are
  released into the lungs and worsen the infection.
• Legionnaires Disease develops 2 10 days after
  exposure to the bacteria. Exposure doesnt
  necessarily lead to infection. About 5 10 of
  the American population show serologic evidence
  of exposure, but never develop symptoms of an
  infection.

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Legionnaires Disease

• Susceptibility
• healthy are relatively resistant
• impairment of respiratory defenses (heavy alcohol
  use, smoking, old age) increases susceptibility
• hospital patients with underlying immune defects
  also susceptible

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Damage to the Lung

• Phagocytes, T cells
• attracted to lung, do not kill bacteria
• release cytokines, other toxic products
• Zinc metalloprotease
• intranasal, intratracheal challenge of guinea
  pigs produces compatible lesions
• similar to Pseudomonas aeruginosa elastase
• enzymatically inactivates IL-2, CD4 receptors on
  T cells could inhibit T cell activation
• antibodies are protective

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Symptoms

• Early symptoms include lethargy, headaches, high
  fever, chills, muscle aches, and anorexia.
• As the disease progresses, a dry, hacking cough
  develops. Half of the people who develop
  Legionnaires Disease suffer shortness of breath
  and a third complain of chest pain.
• Although the pneumonia affects the lungs, the
  disease is accompanied by symptoms that affect
  other areas of the body such as diarrhea, nausea,
  and vomiting.

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Diagnosis

• Clinically, the early stages of Legionnaires
  Disease resemble influenza. The advanced
  symptoms are common to many types of pneumonia.
  Routine laboratory tests will not detect the
  presence of legionella bacteria. Patients who
  have been misdiagnosed as having pneumococcal
  pneumonia will fail to respond to the usual
  penicillin therapy given.
• If a pneumonia case involves multi-system
  symptoms, such as diarrhea and vomiting,
  Legionnaires Disease can be suspected. The
  diagnosis depends on very specialized lab tests
  involving culture of the patients sputum,
  detection of specific antibodies in the patients
  sera, or detecting the organism in urine.

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Diagnosis

• Culture
• Live bacterial cells
• Fluorescent antibody staining
• bacterial antigens
• Gene probes
• bacterial DNA
• PCR
• bacterial DNA
• Clinical tests (urine, antigen, serology)
• antigens/antibodies

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Who Gets Legionnaires Disease?

• Factors influencing susceptibility include the
  elderly, those with suppressed immune systems,
  heavy smokers alcoholics, and others with weak
  lungs. Males are over twice as susceptible as
  females.
• Estimates of the number of cases vary from 25,000
  to 50,000 a year in the U.S., mostly in the
  summer. Between 5 15 of those who contract
  the disease die from it. There have been over 50
  separate outbreaks.

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Treatment

• Most cases show improvement within 12 48 hours
  of starting antibiotic therapy. The antibiotic
  of choice has been erythromycin and for best
  results, it is prescribed together with
  rifampicin.
• Other antibiotics have been used successfully to
  combat the disease, such as doxycycline and
  clarithromycin. The type of antibiotic
  prescribed by the doctor depends on the severity
  of the infection, potential allergies, etc.

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Prevention

• Elimination of L. Pneumophila from the
  environment is impossible. However, elimination
  or reduction of the number of organisms in closed
  systems, such as hospital and hotel water
  supplies and cooling towers, have been achieved
  by means of hyperchlorination or the use of
  disinfectants.
• Studies have shown that high heating of the hot
  water supplies and removal of contaminated shower
  heads and gaskets also have temporarily reduced
  the number of organisms.

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Prevention

• Legionella outbreaks are inevitably linked to
  neglected A/C cooling towers. They are difficult
  to keep clean and usually operate at about 35 ºC,
  within the bacterias optimal growth range.
• Two critical factors for domestic water services
  are water cleanliness and water temperature
  dirty water provides a food supply for the
  bacteria. Colonization is most likely between 35
  40 ºC. It is important to avoid long-term
  storage of water.
• Cooling towers and humidifiers should be examined
  and cleaned regularly. Cooling towers must be
  registered with the local authority and biocides
  may be added to the water.

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RISK MANAGEMENT

• Risk assessment
• Regular monitoring
• Temperature control
• Water Treatment
• Maintenance Cleaning
• Annual review
• Awareness

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