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Estimating the best way forward: Expert and farmer evaluations of environmental interventions to reduce human exposure to E. coli O157. Paul Cross, Dan Rigby & Gareth Edwards-Jones RELU funded ‘Reducing Escherichia coli O157 risk in rural communities’ . Uncertainty & O157 Management.

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slide1
Estimating the best way forward: Expert and farmer evaluations of environmental interventions to reduce human exposure to E. coli O157

Paul Cross, Dan Rigby & Gareth Edwards-Jones

  • RELU funded ‘Reducing Escherichia coli O157 risk in rural communities’
uncertainty o157 management
Uncertainty & O157 Management

Uncertainty regarding:

How people become infected (sporadic infection)

Effectiveness of measures

Likelihood of measures being adopted

is there a problem
Is there a problem?

Many potential measures

+

Absence of hard (e.g. RCT) evidence on measures to reduce risk

+

A (perceived) need to act

= a problem

managing uncertainty
Managing Uncertainty

Identify all possible interventions

Elicit ‘expert’ opinion on interventions

Aim: Identify best candidate interventions

Ideally =

highly effective

+

highly practical

managing uncertainty1
Managing Uncertainty

Which experts?

  • Experts (effectiveness)
    • Inter alia; Public Health, Veterinary Microbiology (Food), Microbiology (Agricultural/Environmental/Clinical), Risk Assessment, Business, Land Management
  • Farmers (practicality)
    • Members of farmers unions in Wales and Scotland.
    • Farmers’ markets

How to elicit their views?

  • Novel method: Best Worst Scaling
best worst scaling
Best-Worst Scaling
  • Market research tool
    • Possible to carry out
      • over distance; no face to face; anonymous
    • Multiple choice based
    • Scaled, fine resolution results
    • Allows respondents to rank long lists without the associated cognitive gymnastics (bite-sized chunks)
best worst scaling analysis
Best-Worst Scaling analysis

Take all the “most effective” & “least effective” choices

5 item set we gain information on 7of the 10 paired combinations

Respondent chooses the two measures with the maximum difference in performance (best and worst)

Maximises the ability to predict peoples choices

intervention generation
Intervention generation
  • Literature review
    • Non-systematic
    • Published and grey literature included
    • Project members
    • Opportunity for experts to add interventions to list
respondent sample
Respondent sample
  • Results of the expert elicitation

Experts (Effectiveness)

Round 1

    • Contacted 53 experts
    • 31(75%) completed survey
    • Reduced initial list of 99 to 30

Round 2

    • Contacted 70 experts
    • 41 (60%) completed survey of 30 interventions

Famers (Practicality)

Round 3

    • 50 in Wales
    • 50 in Scotland
cv scores a measure of agreement
CV scores: a measure of agreement?

Experts had higher CV scores than farmers for ‘effectiveness’ (p<0.001) and ‘practicality’ (p<0.01)

Farmer CV mean scores were very similar between Scotland and Wales.

The mean confidence interval for the practicality assessment was 0.86 for farmers and 1.46 for experts (p<0.001) and for effectiveness was 0.94 and 1.35 respectively (p=0.002).

effectiveness scores
Effectiveness scores

Vaccination

Double

fencing

is there consensus
Is there consensus?
  • Vaccination (Intervention 19)
is there consensus1
Is there consensus?

Reducing stocking densities by 50%

is there consensus2
Is there consensus?

P &E Scores are widely distributed indicating poor agreement amongst respondents

16. HACCP for manure handling

practicality scores
Practicality scores

Hand washing

Reduce cattle stocking

densities by 50%.

slide18

Best-Worst Scaling 2 x 2 plots

Low practicality/

High effectiveness

High practicality/

High effectiveness

19: Vaccination

of cattle

1: Hand washing

27: Reduce cattle

by 50%

12: Septic tank

leakage

Low practicality/

low effectiveness

High practicality/

low effectiveness

method suitability
Method suitability

Best suited to the evaluation of large sets of standalone measures

Best suited to the evaluation of multidimensional measures (effectiveness and practicality)

Smaller multi-level sets of measures, identify the ‘best’ bundles (ACA, CBC)

future
Future
  • Applications in other areas
    • E.g. Cryptosporidium, Salmonella, anti-microbial resistant genes
  • Modelling of interventions
    • % reduction in disease prevalence
  • Development of MACCs
    • % reduction/cost
participating institutions
Participating institutions

Health Protection Agency; Health Protection Scotland; University of Glasgow: School of Veterinary Medicine; Scottish Agricultural Ccollege; Veterinary Laboratory Agency; Scottish Infection Research Network; HPS Colindale; FSA: Microbiological Safety Division; Bioss Scotland; Wageningen University and Research Centre; Liverpool John Moores University: Centre for Public Health; NFUScotland; NFUCymru; Farmers Union Wales; Office of the Chief Veterinary Officer Wales; Meat Promotion Wales; Quality Meat Scotland; Countryside Council Wales