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?