LEGIONELLA AWARENESS SEMINAR for the NORTH WEST WALES HEALTH AND SAFETY GROUP

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LEGIONELLA AWARENESS SEMINAR for the NORTH WEST
WALES HEALTH AND SAFETY GROUP

• by
• Ken Ashley
• formerly
• HM Specialist Inspector HSE
• Dangerous Pathogens Section
• now
• Independent Consultant

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SESSION ONE

• LEGIONNAIRES DISEASE AND LEGIONELLA BACTERIA

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Legionnaires disease

• First recognised July 1976 Philadelphia
• American Legionnaires convention
• 182 cases of pneumonia
• 29 died

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Legionella Hazard or risk?

• The hazard is
• the presence of Legionella bacteria in your water
  system.
• The risk is
• Legionella bacteria growing to a sufficient level
  to cause Legionnaires disease in the population
  exposed

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Legionnaires' disease in Residents of England
Wales by Category of Exposure 1980 to 2004
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What is the real number of cases? Under-reporting

• Estimate 1.
• Countries with best surveillance report 20 cases
  / 106 p.a.
• This suggests in England Wales a total of 52 x
  20 1040 cases p.a.
• Estimate 2
• 2000/2001 - 192,565 cases of pneumonia in
  England in 1 year
• Agent identified in lt5
• Estimates of true incidence of LD based on
  intensive studies of patients in hospital with
  pneumonia caught in the community suggest 2 3
  of all community acquired pneumonias are
  legionnaires disease
• This suggests in England Wales there are about
  5500 cases p.a.

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Legionellosis - an infection caused by Legionella

• Severest - legionnaires disease
• Low attack rate infects less than 5 of
  those exposed
• atypical pneumonia
• symptoms cough - usually dry, 75 fevers 70
  confusion, 45 new sputum, 45 bad headache,
  32 diarrhoea vomiting 30
• up to 40 die (European average 13)
• Incubation (time from exposure to first
  symptoms) 2 10 days
• but sometimes 16 or even up to 21 days (may be
  longer in the immunocompromised)
• Mild - Pontiac / Lochgoilhead fever
• high attack rate affects over 95 of exposed
• influenza like illness no deaths
• incubation 12 48 hours
• Asymptomatic (healthy without symptoms)
• (serological evidence) of exposure to
  infection

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Mode of infection

• Inhalation of organisms suspended in air
• (aerosol - not a spray)
• Rarely by aspiration, maybe significant for
  patients in the dental chair?
• No evidence of person to person
• Factors NB for infection include
• Bacterial burden (infectious dose unknown)
• Effectiveness of dissemination
• Virulence of organism
• Patient susceptibility

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Growth requirements of legionella bacteria

• Grows well between 29oC- 40oC with an optimum of
  35oC
• Will grow between 20C and 45C
• Below 20C legionella survives but does not grow
• Above 50C legionella is killed
• Food e g sludge in a calorifier
• Presence of cysteine(an amino acid) and iron
• Iron increase growth 10,000 to 100,000 fold

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Susceptibility to physical and chemical agents

• Heat eg hot water above 50C and particularly
  above 60C as used in hot water storage
• Biocides used in hot and cold water services
  where temperatures cannot be achieved such as
  chlorine dioxide or silver ions

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Cultural characteristics

• Do not grow on ordinary nutrient media
• Up to 14 days to grow legionella
• Reminder-monitoring is a snapshot
• Reminder-monitoring is not control
• Most clinically important bacteria grow within 18
  to 24 hours
• Reminder-dip slides do not detect legionella
  bacteria

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Identification

• Culture-for both patients and plant
• Urine antigen(patients)
• Antibody(patients)
• Gene probe(both but will detect dead organisms in
  plant as well as live)

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Habitat

• Wide-spread in natural water sources
• Rivers and lakes - therefore in the water supply
• Mud and soil
• Then will enter into many man made systems eg hot
  and cold water systems, cooling towers etc as
  less sensitve to chlorine than most waterborne
  bacteria.
• Therefore you cannot avoid it entering your
  practice

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Habitat

• Biofilm
• Other organisms are needed, particularly ameobae
  in a water system that graze on the
  water/suface interface eg the inner surface of a
  pipe
• When legionella bacteria burst from an amoeba
  there are about 10,000 released into the water

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Pathogenicity

• Mainly, L. pneumophila serogroup 1 and 6
• L. micdadei, L. dumoffi
• You need to know the name of the organism in
  bullet point one as this is the one that causes
  90 of cases/outbreaks

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Statistics summary

• 600 or so cases per year(much higher in 2002
  because of Barrow)
• MOST cases are caused by HCW
• 50 possibly travel associated if you include
  returning to an infected water system at home
• Usually 10-12 mortality(in hospitals up to 40)
• Males more likely to be affected (31)

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Conditions required for proliferation

• Water containing legionella (inevitable)
• Temperature between 20C and 45C, noting that
  the maximum growth is between 30C and 40C
• Food source eg organic debris such as leaves or
  animal access to cold water tanks
• Stagnation eg blind ends or surfaces beneath
  scale and rust as often found in old domestic
  (some of your practices) hot and cold water
  systems

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Factors promoting infection

• Presence of airborne droplets containing viable
  legionella
• Chain of events
• Presence of legionella
• Conditions suitable for multiplication/proliferati
  on to high numbers
• Means of creating breathable droplets
• Exposure of susceptible person

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Who is most susceptible?

• Men more than women ( 3 1)
• Aged gt 50 years
• Smokers
• Heavy drinkers
• Diabetics
• Chronically ill
• Immuno-suppressed
• transplant patients
• Steroid treatment

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BARROW IN FURNESS

• July/August 2002
• Approximately 175 infected and 7 deaths
• Stafford in 1985 was 100 cases and 28 deaths
• Associated with a cooling tower used to reject
  heat from an air conditioning system

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Summary

• Moisture/water needed
• Temperature between 20oC and 450C
• Nutrients from sediment, sludge, scale,
  compatible organisms and materials used in
  construction
• Presence of biofilm, stagnation and conditions to
  promote proliferation
• Breathable droplets