Guidance on microbial risk assessment. Gertjan Medema

Transcription

1 Guidance on microbial risk assessment Gertjan Medema 1

2 Microbial risk assessment 2

3 Guidance on QMRA

4 Content of chapter Context of MRA: food safety management Process of MRA: guidance to documents/sites Review of MRA in fresh produce and processing Case studies Value of MRA in fresh produce and processing 4

5 Context: food safety management Objective of microbial risk assessment is to facilitate adequate microbial risk management HEALTH TARGETS Acceptable risk Risk Management Assess Environmental Exposure Assessment of risk PUBLIC HEALTH STATUS From: Fewtrell & Bartram, in Water Quality Guidelines, Standards and Health (WHO). IWA publishing. WHO: Stockholm framework for safe water ILSI

6 Process of MRA (Risk ranking tool Anderson et al 2011) Wastewater irrigation and health Irrigation of fresh produce underrepresented Wiki.camra.msu.edu decode= xfooddb.htm EPA exposure handbook Australian water recycling guidelines Uncertainty analysis guidance (literature) Software tools (ILSI, 2012) ILSI

7 Case study Australia Secondary treatment with lagoons Wastewater reuse for fresh produce (unrestricted)?

8 Hazard identification Wastewater may contain a wide range of pathogens Selection of reference pathogens Parasites: Cryptosporidium (small, resistant, infectious) Viruses: Adenovirus/Rotavirus (infectious, available data) Bacteria: Campylobacter (very prevalent, infectious)

9 Risk assessment Water reuse guidelines Australia [Pathogen] wastewater Application System performance requirements Health target

10 Risk assessment Water reuse guidelines Australia [Campylobacter] Wastewater 7000/L Australian data (95%) Application System performance requirements Health target <10-6 DALY Australian target

11 Risk assessment Water reuse guidelines Australia [Campylobacter] Wastewater 7000/L Application System performance requirements Annual dose <0.037 pp

12 Exposure assessment Water reuse guidelines Australia Concentration of reference pathogens in wastewater Exposure through various applications

13 Risk assessment Water reuse guidelines Australia [Campylobacter] Wastewater 7000/L Commercial crop irrigation System performance requirements 5.0 log Annual dose <0.037 pp Exposure pppy Total: Lettuce: Other raw food crops: 490 ml 70 x 5 ml 140 x 1 ml <0.075/L

14 System performance Step Cryptosporidium removal (log) Rotavirus removal (log) Campylobacter removal (log) Required removal Secondary treatment Lagoon detention Total

15 System improvement Step Cryptosporidium removal (log) Rotavirus removal (log) Campylobacter removal (log) Required removal Secondary treatment Lagoon detention Filtration Disinfection With-holding period Total

16 Application MRA Water reuse guidelines Australia QMRA used in wastewater reuse guidelines. to set performance targets for reuse systems that are application specific based on a predefined health target using exposure data from scientific literature to select appropriate combination of control measures

17 Expected illnesses/10000 servings Case study Sweden Scenario evaluation Expected illnesses/10000 servings EHEC outbreak lettuce Guidelines irrigation water quality E.coli <100/100mL 48 h withholding period MRA: evaluate contribution of other control measures Rinsing, extra withholding time, different standards Water quality guideline 100 Ecoli/100ml Water quality guideline 1000 Ecoli/100ml Holding time (days) no rinse 1000 rinse Value for risk management: underpin guidelines and communication about value of rinsing Holding time (days) no rinse rinse

18 Best value of MRA MRA is a systematic, objective, transparent, evidence-based approach to assess the health risks associated with fresh produce, and hence evidence-base for risk management MRA can evaluate different exposure scenarios and intervention options and guide risk management to select best options MRA provides the level of safety management necessary to achieve the health-based targets MRA guides the risk manager to the contribution of individual control measures (in water treatment, irrigation/farm/food handling practice) to the overall, multiple barrier control strategy

19 Needs Health-based targets for safe reuse of wastewater in irrigation: applicable in practice Data for exposure assessment (incl. validity of indicators) International repository of state-of-the-science data

20 Acknowledgements Co-authors: Lee-Ann Jaykus, David Cunliffe, Marcelo Signorini, Charles Gerba, Maria Tereza Pepe Razzolini, Flavio Zambrone, Vittorio Fattori, Marisa Caipo 20

21 Good MRA practice (WHO 1999; EFSA 2009) Scope and objectives clearly defined with risk manager Clearly separate from risk management Soundly based on science Transparent Data evaluated for quality and relevance (taking into account their overall weight in the risk and uncertainty) All data documented and referenced Take variability into account in the MRA (probabilistic) All assumptions documented, explained and sensitivity of MRA tested Describe uncertainties and their relative influence on the outcome, preferably quantitative (probabilistic) Conclusions reflect objectives and scope, include uncertainties/assumptions