Transcript 1) Legionella Bacteria - North West Wales Health & Safety Group

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
SESSION ONE
LEGIONNAIRES’
DISEASE AND
LEGIONELLA BACTERIA
Legionnaires’ disease
• First recognised July 1976
Philadelphia
• American Legionnaires’ convention
• 182 cases of pneumonia
• 29 died
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
Legionnaires' disease in Residents of
England & Wales by Category of
Exposure 1980 to 2004
600
NOSOCOMIAL
COMMUNITY
TRAVEL UK
TRAVEL ABROAD
Number of Cases Reported
500
400
300
200
100
0
80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03
4 06#
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 <5%
–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.
•
•
•
•
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
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
Growth requirements of
legionella bacteria
• Grows well between 29oC- 40oC with an
optimum of 35oC
• Will grow between 20°C and 45°C
• Below 20°C legionella survives but does not
grow
• Above 50°C 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
Susceptibility to physical and
chemical agents
• Heat eg hot water above 50°C and
particularly above 60°C 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
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
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)
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
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
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
Statistics summary
• 600 or so cases per year(much higher in
2002 because of Barrow)
• MOST cases are caused by H&CW
• 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 (3:1)
Conditions required for
proliferation
• Water containing legionella (inevitable)
• Temperature between 20°C and 45°C, noting
that the maximum growth is between 30°C and
40°C
• 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
Factors promoting infection
• Presence of airborne droplets containing
viable legionella
• Chain of events
– Presence of legionella
– Conditions suitable for
multiplication/proliferation to high numbers
– Means of creating breathable droplets
– Exposure of susceptible person
•Men more than
women ( ≈ 3 : 1)
•Aged > 50 years
•Smokers
•Heavy drinkers
•Diabetics
•Chronically ill
•Immuno-suppressed
–transplant patients
–Steroid treatment
Number of Cases
Who is most susceptible?
1000
900
800
700
600
500
400
300
200
100
0
0-9
10-19
20-29
30-39
40-49
50-59
60-69
Age Range
Males
Females
70+
NS
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
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