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?

PolicyGuidleines

Local experiences

Research

Implementation”in practice”

Theory, basic

research

DisseminationCommunicatio

nEducation

Risk management – policy development

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

Wastewater generation

Consumer

Wastewater treatment

Safe produce

…

Wastewater generation

Consumer

Wastewater treatment

Safe produce

…

WHO’s multiple barrier approach from “Farm to Fork”

Wastewater generation

Farmer/ Producer

Traders/Retailers

Street food kitchens

Consumer

Wastewater treatment

Safe irrigationpractices

Hygienichandlingpractices

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

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

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

Microbial analysisIndicators not always reliable

Epidemiological studiesScarce, complex

Microbial risk assessmentThe main approach (?)

Assessment of health risks

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

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)

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)

Input: faecal contamination, prevalence of infection,excretion densities, excretion days, inactivation rates

Scenarios:

Dose-response models Output: probability of infection

Exposure Risk

Cleaning of blocked pipes Ingestion ofpathogens

Accidental ingestion whenhandling unstored urine

Ingestion ofpathogens

Accidental ingestion whenhandling stored urine

Ingestion ofpathogens

Inhalation of aerosolscreated when applying urine

Inhalation ofpathogens

Consumption of cropsfertilised with urine

Ingestion ofpathogens

(Höglund et al., 2002)

Microbial risk assessment – urine (outline)

C. jejuni C. parvum Rotavirus

log 1

0 P

inf

-6

-5

-4

-3

-2

-1

0

epidemic sporadic 4°C sporadic 20°C

• Unstored urine Pinf < 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

Time between crop fertilising and consumption

log 1

0 P

inf

-15

-14

-13

-12

-11

-10

-9

-8

-7

-6

-5

-4

-3

-2

-1Campylobacter Cryptosporidium Rotavirus

<10-15

1 week 2 weeks 3 weeks 4 weeks

• 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

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)

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)

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)

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)

Hässleholm municipality with 28 600 residents

12 500 m3 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)

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)

Exposure scenarios – wastewater treatment

12

3, 4

5

67

8

(Westrell et al., 2004)

 

Type of exposureVolume ingested

(mL or g)Frequency

(times*year-1)

Number of persons affected

1. WWTP worker at pre-aeration 1 52 2

2. WWTP worker at belt press 5 208 1

3. (Un)intentional immersion at wetland inlet

30 1 2

4. Child playing at wetland inlet 1 2 30

5. Recreational swimming 50 10 300

6. Child playing at sludge storage 5 1 2

7. Contractor spreading sludge 2 30 2

8. Consumption of raw vegetables 1 2 500

Exposure scenarios – wastewater treatment

(Westrell et al., 2004)

Risk of infection per exposure

All risks >10-4 are shown in orange

(Westrell et al., 2004)

Exposure EHEC Salmonella Giardia Cryptosporidium Rotavirus Adenovirus

1 1.98

(1.69-2.00) 1.99

(1.30-2.00)

2 0.57

(0.05-0.99)

1.00 (0.99-1.00)

1.00 (0.97-1.00)

3 0.21

(0.02-1.87)

4 0.23

(0.02-5.21)

5 0.18

(0.01-4.26)

6 0.76

(0.23-1.28) 1.87

(0.22-2.00)

7 0.52

(0.04-1.75) 0.13

(0.006-1.25) 2.00

(1.64-2.00) 2.00

(1.49-2.00)

8 0.41

(0.01-20.51)

0 is equivalent to <0.0001 infections

Number of yearly infections

(Westrell et al., 2004)

Severity of hazards

(Westrell et al., 2004)

Exposure EHEC Salmonella Giardia Crypto. Rotavirus Adenovirus

1 Median

95-percentile

2

3

4

5

6

7

8

Catastrophic Major Moderate Minor Insignificant

Classification of exposures

(Westrell et al., 2004)

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)

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)

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)

107 households, 449 people Prevalence of parasitic infections Type of latrines

UD solar desiccating latrine (single vault) UD double-vault desiccating latrine (LASF)Pit latrinesNo latrines

UD = urine diverting

Epidemiological study - El Salvador

(Corrales et al., 2006)

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)

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)

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

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

2

88

10

Pit/VIP No sanitation UD

14

7

79

Pit/VIP No sanitation Flush

Exposed Area (N=660)

Unexposed Area (N=667)

Type of Sanitation Intervention in Sample Area

Provided by Renuka Lutchminarayan

(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

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

Female Male Total

Gender

Inci

den

ce R

ate

per

100

0 p

erso

n d

ayss

Non-exp Exp

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)

Impacts on diarrhoeal disease reduction by interventions

Intervention areaReduction in diarrhoea

frequency

Hygiene 37%

Sanitation 32%

Water supply 25%

Water quality 31%

Multiple 33%

(In WHO, 2008, adapted from Fewtrell et al., 2005)

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