Transcript Legionella sp.

Legionella sp.
Legionnaire’s Disease
Pontiac Fever
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, > half implicated in
human disease
– L. micdadei: mild, febrile, flu-like illness called
Pontiac fever
• self-limiting, little or no tissue damage
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.
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.
Ecology
• Environmental conditions which promote the
growth of legionella are:
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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.
Ecology
• The range of temperatures within which legionella
survives and thrives:
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.
RISK AREAS
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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)
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
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 doesn’t necessarily lead to infection. About 5 –
10% of the American population show serologic evidence of
exposure, but never develop symptoms of an infection.
Legionnaire’s 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
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
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.
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 patient’s sputum, detection of
specific antibodies in the patient’s sera, or detecting the
organism in urine.
Diagnosis
• Culture
Live bacterial cells
• Fluorescent antibody staining
bacterial antigens
• Gene probes
bacterial DNA
• PCR
bacterial DNA
• Clinical tests (urine, antigen, serology)
antigens/antibodies
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.
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.
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.
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 bacteria’s
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.
RISK MANAGEMENT
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Risk assessment
Regular monitoring
Temperature control
Water Treatment
Maintenance & Cleaning
Annual review
Awareness
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