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Legionellae and the Opportunistic Bacterial PathogensRisk Assessment and Risk Management
Dr Michael StoreyPublic Health Research and Development, Sydney Water
International Keynote June 2007
Background and Introduction
Legionellae and the Opportunistic Pathogens
- Pathology
- Ecology
Risk Assessment
- Qualitative
- Quantitative
Risk Management
- Framework
- Water Safety Plans
- Legislation
Ecology and Pathology of the Opportunistic Bacterial Pathogens
Definition: Organism that can cause disease in individuals with a compromised immune (defence) system
Primary defence
- Burns, cuts, abrasions
Secondary defence (immune system)
- HIV, elderly, infants, sick, transplant, cancer patients, diabetics
20% of the population
Diagnosis 1 in 100,000
Seroprevalence 1 in 10,000
Opportunistic Pathogens
Opportunistic PathogensAeromonas hydrophila
Burkholderia spp.
Enterobacteriae
Klebsiella, Proteus and Serratia spp.
Legionella pneumophila
Mycobacterium avium (MAC)
Pseudomonas aeruginosa
Acanthamoebae
Naegleria fowleri
Environmental reservoir
- No secondary transmission
- Sporadic infection
Association with free-living protozoa
- Site of reproduction in the environment
- Evolutionarily related to macrophage
- Trigger virulence factors
- Protect from conventional disinfection
Cooling towers, spas
Accidental pathogen?
Opportunistic Pathogens
Qualitative and Quantitative Risk Assessment
Qualitative Risk AssessmentEnvironmental exposure and
outbreaks of disease
- Lack of reliable data
Health-based targets
Based on best available information
- Legionella incidence and infection
Guidelines
Water Safety Plans
27 June 2016
Sewer worker health study (Medema et al., 2004)
- 105 per mL in sewage
- 0.56 – 56 per m3 in air
Qualitative Risk Assessment
Location
Illness Legionella.m3 Reference
Shower no 4.7
Tap no 8.1 Bollin et al., 1985
Shower no 0.33 Dennis et al., 1984
Air condenser yes 2300
Shower yes 190 Breimann et al., 1990
Cooling tower ? 20 - 2580 Tyndall et al., 1985
Sewage treatment no < 0.1 - < 1
Sewage treatment no < 0.56 - 56 Medema et al., 2004
Quantitative Risk AssessmentQuantitative Microbial Risk Assessment
1. Hazard identification
2. Exposure assessment
3. Dose-response assessment
4. Risk characterisation
Hazard identification
- Pathogenicity of the organism
- Host-pathogen interaction
- Incidence in the environment
- Surveillance, monitoring
27 June 2016
Rouse HillFyshwick
Carrum
BolivarMarvel Loch
Broome
Darwin
Hazard Identification
27 June 2016
Exposure Assessment
Respirable fraction (<5 m)
Inhalation rate 30 breaths/minute
Tidal volume 500 mL
2 L water.minute-1
Aerosol Diameter (μm) Aerosol Concentration /cm3 Aerosol mass ng/cm3
1.3 180 - 660 0.2 - 0.7
2.1 90 - 320 0.4 - 1.4
3.4 40 - 120 0.8 – 2.3
5.5 20 – 60 1.6 – 4.8
Total 360 – 1200 2.9 – 9.2
(Mercer, 1999)
Exposure Assessment
Culture based methods
- Impactor
- Liquid impinger
- Filtration
- Reproducibility, selective
- Sensitivity, qualitative
Non-culture based methods
- Fluorochromes, FISH
- ELISA, PCR
- Complicated, labour intensive
- High cost, viability?
Lack of reliable dose-response data
- Semi-quantitative
- Expert opinion
Generated in animal models
- 10 and < 129 infectious units
- Rabbits
- Guinea pigs
Aeromonads
Dose-Response Assessment
Risk CharacterisationBeta-Poisson
- Pinf = 1 – (1 + N/β)-α
Exponential risk model
- Maximum Risk Curve
- Pinf = 1 – e-rD
- 1 infectious unit results in illness (r = 1)
- Overestimate risk
- Immunocompromised
Input Parameter Input Value
therm. disinfection (°C) 50, 60, 70, 80
free chlorine (mg.L-1) 1, 2, 5, 10
comb. chlorine (mg.L-1) 1, 2, 5, 10
Legionella (10x.cm-2) triangular (2, 3, 6)
biofilm detached (%) discrete (10, 50, 90)
water inhaled (μL) log normal (58 ± 36)
Risk Management: The Framework, Water Safety Plans and Legislation
Framework for Safe Drinking WaterFramework for the Management of Drinking Water Quality (CRC for Water Quality and Treatment, 2004)
Australian Drinking Water Guidelines(NHMRC, 2004)
Guidelines for Drinking Water Quality 3rd Edition, (WHO, 2004)
Bonn Charter (IWA & WHO, 2004)
National (Australian) Guidelines for recycled and recreational waters
27 June 2016
Framework for Safe Drinking WaterGuidelines for Safe Recreational Water Environments (WHO, 2006)
Health Aspects of Plumbing (WHO, 2006)
Guide to Ship Sanitation (WHO, 2007)
Legionella and the Prevention of Legionellosis (WHO, 2007)
- Risk Assessment and Risk Management
- Source, Ecology and Identification
- Prevention and Control
- Policies and Practices
- Water Safety Plans
27 June 2016
Health-based targets
- Qualitative risk assessment
- Outbreaks of disease
Surveillance
- Audit by Health Department
Water Safety Plans (WSP)
- Adapted from DWG (WHO, 2004)
- System assessment
- Monitoring
- Management and Communication
Legionella and the Prevention of Legionellosis (WHO, 2007)
27 June 2016
WSP – System AssessmentAssemble a team
- Experience and understanding
- Multi-disciplinary
Document and describe the system
- Identify layout and design
- Design faults and maintenance
Assess hazards and prioritise risks
- Susceptible population
- Understand hazards
Assess the system
- Flow diagram
- Exposure pathways, control points
WSP – MonitoringIdentify control measures
- Excluding microorganisms
- Environment
- Nutrients, hydraulics, temperature
- Biocide
Monitor control measures
- HPC <10 000 cfu/mL
- Keep records
Validate effectiveness of WSP
- Verification of system assessment
- Extensive, intensive monitoring
WSP – Management and CommunicationDevelop supporting programs
- Training and education
- Data on health-related targets
Prepare management procedures
- Incident management
- Identify responsibilities
Establish documentation and communication
- Personnel
- Maintenance strategies
- Records
Melbourne AquariumApril 2000 – 80,000 visitors
125 confirmed cases (1.3 cases per1000 visitors) in April 2000
95 hospitalised, 4 deaths
23 to 89 years (median 64 years)
L. pneumophila Serogroup 1 (3000 – 6900 cfu per mL)
First risk-based legislation in Australia (DHS, 2001)
27 June 2016
Australian LegislationPublic Health Act. (1991)
Public Health Regulation (2000)
NSW Code of Practice for the control of Legionnaire’s Disease (NSW Health, 2004)
A Guide to Developing Risk Management Plans for Cooling Tower Systems (DHS, 2001)
- Registration of system
- Risk Management Plan (cf. WSP)
- Maintenance program
- Records of monitoring and maintenance
ConclusionLegionellae and the Opportunistic Pathogens- Ecology and pathology
- Free-living protozoa
Risk Assessment- Dose-response relationship
- Qualitative and semi-quantitative
Risk Management- Framework
- Water Safety Plans
Questions?