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3.5 Risk management Learning objective: To be aware of how sanitation systems can be evaluated and compared regarding their potential health impact. To.

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Presentation on theme: "3.5 Risk management Learning objective: To be aware of how sanitation systems can be evaluated and compared regarding their potential health impact. To."— Presentation transcript:

1 3.5 Risk management Learning objective: To be aware of how sanitation systems can be evaluated and compared regarding their potential health impact. To be familiar with the different parts of Quantitative Microbial Risk Analysis (QMRA). Can we measure a risk of disease transmission? How can sanitation systems be evaluated?

2 Theory, basic research Dissemination Communication Education Risk management – policy development

3 The most important barrier to manage risks? Handling (contact) of excreta should be minimized, but necessary to some extent What is practically, socially and culturally acceptable? Adapted to local conditions, education and information, sustainability Treatment recommendations important part of the guidelines Will develop, on-going research Treatment as a health protection measure

4 Wastewater generation Consumer Wastewater treatment Safe produce … Wastewater generation Consumer Wastewater treatment Safe produce … WHOs multiple barrier approach from Farm to Fork Wastewater generation Farmer/ Producer Traders/ Retailers Street food kitchens Consumer Wastewater treatment Safe irrigation practices Hygienic handling practices Safe food washing and preparation Awareness creation to create demand for safe produce Policy recognition, safer farm land, tenure security, market incentives, safe-food labelling,… Risk reduction strategies

5 Treatment define processes, different levels (categories) Validation of the treatment process Microbiological/hygienic quality presence of microorganisms, reduction of microorganisms Restrictions on usage Fertilising (irrigation) methods Handling of the product (e.g. transport, storage) Protection of workers Sampling Analytical methods Examples of how to design regulations

6 Diverted Small volumes Easier to treat Suitable fertiliser products Handling requires restrictions Mixed (conventional) Large volumes of hazardous waste Extensive treatment Reuse products: wastewater, sludge Downstream pollution Comparison of sanitation systems

7 Microbial analysis Indicators not always reliable Epidemiological studies Scarce, complex Microbial risk assessment The main approach (?) Assessment of health risks

8 Risk Assessment Qualitative or quantitative Systematic procedure Acceptable risks Risk Management To handle the risks Aims at reducing risks Risk Communication Essential part in all systems Necessary for awareness raising and health protection Involve all stakeholders Microbial Risk Analysis

9 Hazard Identification All enteric pathogens potentially in excreta Exposure assessment Exposure points, site-specific data on removal Literature data on occurrence of pathogens, removal in treatment and survival in environment Exposure scenarios evaluated (ingestion, volumes) Dose-response assessment Published mathematical models Risk characterisation Risk of infection per exposure and yearly, DALYs Comparison with endemic level of disease (underreporting) Quantitative Microbial Risk Assessment (QMRA)

10 Faecal contamination Faecal sterols analysed What amounts of pathogens would the faecal contamination contribute? Incidence in the population (statistical data) Faeces could contribute enteric pathogens to the urine IF they end up in the urine – will they survive storage? Survival studies performed and literature data used for crop How can people be exposed to the urine? Scenarios determined What dose could they be exposed to? Amounts ingested estimated (Höglund et al., 2002) Microbial risk assessment – urine (outline)

11 Input: faecal contamination, prevalence of infection, excretion densities, excretion days, inactivation rates Scenarios: Dose-response models Output: probability of infection (Höglund et al., 2002) Microbial risk assessment – urine (outline)

12 Unstored urine P inf < 1:1000 except for rotavirus Storage for six months at 20°C all risks < 1:1000 (Höglund et al., 2002) Risk from accidental ingestion of 1 ml unstored urine

13 Inactivation will continue in the field Risk dependent on time between fertilising and consumption (Höglund et al., 2002) Risk from accidental ingestion of 100 g crop

14 Faeces from dry urine diverting latrines in Denmark No additives Treatment by storage Hazard identification Bacteria: Salmonella, EHEC Viruses: rotavirus, hepatitis A Protozoa: Giardia, Cryptosporidium Helminth: Ascaris Compiled studies (literature) for pathogen survival Incidence (surveillance), excretion numbers and times (duration) also input for calculation of doses Model organisms – dose-response relation Exposure when handling and using in garden Microbial risk assessment - faeces (Schönning et al., 2004)

15 The faeces-soil intake (Larsen,1998) - children around 200 mg of soil (max of 5-10 g). Assumed that adults ingest 15-50% of this amount, with a maximum of 100 mg. The container emptied once a year assuming only adults exposed. The number of exposures through recreation was a median value of 3.5 times per week (during June-August). 50% of the households were exposed through gardening once a week (during May-September). It was assumed that one exposure corresponded to two hours of gardening occurring a maximum two times per day. Exposure scenarios (Schönning et al., 2004)

16 There is an unacceptably high (>1:10 000) risk of infection when faeces is used without treatment The highest risk from exposure to unstored material was attributable to rotavirus 12 months storage – sufficient reduction of most pathogens (compared to a risk level 1:10 000) The highest risk from exposure to stored faeces was attributable to Ascaris the protozoa Giardia and Cryptosporidium are of greater concern in the European population The risks of infection can be reduced by simple measures such as longer storage, or treatment with a pH elevating compound Conclusions - pathogens (Schönning et al., 2004)

17 Risk for infection when emptying container Salmonella Ascaris Examples of how risk for infection are presented as probability density functions. The typical risk equals the 50th-percentile and worst case equals the 95th-percentile. (Schönning et al., 2004)

18 Hässleholm municipality with 28 600 residents 12 500 m 3 wastewater per day Wastewater treatment: pre-aeration, pre- sedimentation, activated sludge, chemical precipitation, three-media filter Sludge treatment: anaerobic digestion, dewatering, outdoor storage Sludge use: Application to vegetables (theoretical) Microbial risk assessment – wastewater and sludge (Westrell et al., 2004)

19 Hazard Identification All entero-pathogens potentially in wastewater Enterohaemmorhagic E.coli (EHEC), Salmonella, Giardia, Cryptosporidium, rotavirus and adenovirus Exposure assessment Exposure points identified together with WWTP staff Site-specific data on removal of indicators in WWT Literature data on occurrence of pathogens in ww, removal in sludge treatment and survival in environment Dose-response assessment Published dose-response models Risk characterisation Monte Carlo simulations Risk of infection per exposure Yearly number of infections in study population Comparison with endemic level of disease (epidemiological statistics adjusted for underreporting and morbidity rates) Microbial risk assessment – wastewater and sludge (Westrell et al., 2004)

20 Exposure scenarios – wastewater treatment 1 2 3, 4 5 6 7 8 (Westrell et al., 2004)

21 Type of exposure Volume ingested (mL or g) Frequency (times*year -1 ) Number of persons affected 1. WWTP worker at pre-aeration1522 2. WWTP worker at belt press52081 3. (Un)intentional immersion at wetland inlet 3012 4. Child playing at wetland inlet1230 5. Recreational swimming5010300 6. Child playing at sludge storage512 7. Contractor spreading sludge2302 8. Consumption of raw vegetables12500 Exposure scenarios – wastewater treatment (Westrell et al., 2004)

22 Risk of infection per exposure All risks >10 -4 are shown in orange (Westrell et al., 2004)

23 Number of yearly infections (Westrell et al., 2004)

24 Severity of hazards (Westrell et al., 2004)

25 ExposureEHECSalmonellaGiardiaCrypto.RotavirusAdenovirus 1 Median 95-percentile 2 3 4 5 6 7 8 CatastrophicMajorModerateMinorInsignificant Classification of exposures (Westrell et al., 2004)

26 Exposure 1 Easy to control with Personal Protective Equipment (PPE) Covering of basins Exposure 2 Easy to control with PPE Optimisation of sludge treatment (baffles against short-circuiting, thermophilic digestion etc.) Control measures (Westrell et al., 2004)

27 Exposure 6 Fence storage area Optimisation of sludge treatment Exposure 7 Use of PPE Optimisation of sludge treatment Prolonged sludge storage Control measures Exposure 8 Crop restrictions Minimum time between fertilisation and harvest Optimisation of sludge treatment Prolonged sludge storage (Westrell et al., 2004)

28 Per-Åke Nilsson and staff at Hässleholm wastewater treatment plant Swedish research council FORMAS MISTRA Urban Water program Acknowledgements Worst-case situation 2002 (Westrell et al., 2004)

29 107 households, 449 people Prevalence of parasitic infections Type of latrines UD solar desiccating latrine (single vault) UD double-vault desiccating latrine (LASF) Pit latrines No latrines UD = urine diverting Epidemiological study - El Salvador (Corrales et al., 2006)

30 Prevalence of parasitic infections Use of UD-latrines (both solar and LASF) – lower prevalence of the less environmentally persistent pathogens (hookworm, Giardia, Entamoeba) Use of LASF – higher prevalence of more environmentally persistent pathogens (Ascaris, Trichuris) (Corrales et al., 2006)

31 LASF (this design) does not achieve conditions needed to inactivate these organisms UD solar latrines – lower prevalence of most parasites compared with LASF and pit-latrine Use of biosolids (faecal matter) in agriculture – higher prevalence of infections compared to burying the material Summarised results (Corrales et al., 2006)

32 In El Salvador, the solar latrine is recommended Includes urine diversion Better results than pit latrine High prevalence of some infections in diverting latrines identifes the need for Further work on better designs Better use and maintenance, information Further evaluation under different local environments and cultures Limitations of the study Different communities compared Small sample size Conclusions

33 Epidemiological study South Africa Peri-urban area, eThekwini Municipality, Durban 1337 households incl. in study Intervention Sanitation – dry UD-toilets Safe water (200 L per day) Health and hygiene education Purpose and method Measure reduction in diarrhoea associated with the interventions Prospective cohort study Disease incidence questionnaire (6 visits) (Knight et al., manuscript) Picture provided by Teddy Gounden

34 Exposed Area (N=660) Unexposed Area (N=667) Type of Sanitation Intervention in Sample Area Provided by Renuka Lutchminarayan

35 (Knight et al., manuscript) Epidemiological study South Africa - Results 41% reduction in diarrhoea Benefits 3 times greater for children <5 years Fewer acute water related health outcomes Duration of diarrhoea episodes decreased (54% fewer days reported) Not possible to disaggregate the effect of each separate intervention Picture provided by Teddy Gounden

36 36 Incidence Rate & Incidence Rate Ratio of Diarrhoea Episodes by Gender & Total IRR: 0.50 IRR: 0.65 IRR: 0.58 (Knight SE, Esterhuizen T, Lutchminarayan R, Stenström T-A)

37 Impacts on diarrhoeal disease reduction by interventions Intervention area Reduction in diarrhoea frequency Hygiene37% Sanitation32% Water supply25% Water quality31% Multiple33% (In WHO, 2008, adapted from Fewtrell et al., 2005)

38 Different types of studies Possible to investigate the real situation? Epidemiology – underestimation in disease incidence Interviews, surveillance Risk assessments – assumptions made, over- or underestimating risks (?) Sampling and microbial analysis Illustrates the importance of various studies Range of interventions possible and needed in combination Difficult to differentiate effects Identifying need of risk management and barriers Health protection measures of different kinds Summary of module on risk management

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