Benefits and pitfalls of Cryptosporidium risk assessments

1
Benefits and pitfalls of Cryptosporidium risk
assessments

• Dr Colin Fricker
• CRF Consulting
• UK

2
Whenever there is a crypto outbreak someone
either

• Loses their job
• Is prosecuted
• Gets sued
• All of the above

3
What is risk assessment?
Risk assessment is the determination of
quantitative or qualitative value of risk related
to a concrete situation and a recognized
threat. Cryptosporidium risk assessments are at
best semi-quantitative!!
4
What does this mean?

• Consumption of water carries a risk dependent on
  the source of the water and the efficiency of
  treatment
• The risk to consumers is dependent on conditions
  at any given time
• Changes in catchment conditions and treatment
  plant performance alter the risk

5
Why do risk assessments?

• Understand risk to the population
• Understand treatment plant performance
• Understand your catchment
• Identify areas of concern
• Identify things to fix!!!
• Because you are told to!!!

6
The meaning of risk assessments

• The risk to consumers varies with time
• Risk assessments need to take account of the
  variation in catchment conditions
• Variation in treatment plant performance presents
  the largest risk to consumers
• Studying the catchment alone does little to
  establish the risk
• Need to be considered as part of a WSP
• Risk assessments do not protect public health,
  actions related to WSPs do!!

7
Assessing the catchment

• Agricultural activity
• Sewage treatment plants
• Septic tanks
• Dilution
• Distance
• Seasonality

8
What factors are important?

• Type of animal (type of crypto)
• Animal age
• Control of run off (type of faeces)
• Efficiency of sewage treatment
• Overflows during rain events

9
Should you monitor?

• Monitoring gives an indication of the likely
  level of contamination at any given time
• Monitoring should be used to validate risk
  assessment
• Should incorporate protozoa and bacterial
  monitoring
• Can give a false impression

10
The truth about parasite monitoring

• It is expensive!
• Hugely variable
• Does not determine infectivity
• Requires expert interpretation
• Does little to determine risk
• Requires specialised analysis to be meaningful

11
Deficiencies of traditional risk assessments

• Usually overestimates risk
• Ignores species specificity
• Does not assess STW effectiveness
• Often based on average conditions
• Does not include detailed assessment of WTP
  performance

12
Recommendations for risk assessment

• Assess credentials of the assessor
• Ensure familiarity with protozoa
• Do a detailed assessment of the catchment
• Have plant performance data analysed carefully
• Identify critical control points
• Identify potential improvements to treatment
• Identify remedial measures in the catchment

13
Recommendations for risk assessment

• Ensure any monitoring is appropriate
• Obtain advice on monitoring programs and data
  interpretation
• Insist on internal controls for monitoring
• Study the risk report carefully
• Dont ignore the findings!!!