Transcript Discussion on WHO Guidelines on Evaluation of Household

Regu P. Regunathan PhD
ReguNathan & Associates, Inc.
Technical Consultant to WQA
10 Aug 2011
Guidelines released
• Released in June 2011 after considerable reviews and
discussions
• Intended Audiences are:
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National Certifiers
Regulatory Authorities
Researchers
Manufacturers & Implementers
• Arranged in 3 short Sections and 4 detailed
Appendices
Tiered Approach
 One of the most contentious subject by reviewers
 Modified from original proposal but still retained the
essence of the concept . Interim Target approach has
been altered significantly.
 Based on WHO’s regularly and extensively used target
levels of DALY (Disability Adjusted Life Years)
 Quantitative Microbial Risk Assessment (QMRA) was
employed to estimate Health based Performance
Targets
DALY
 Measure to estimate burdens of disease and injuries
 Health effects weighed - 0 (good health) to 1 (death)
 Years of life lost due to mortality = YLL
 Years of life lived with disability = YLD
 DALY = YLL + YLD
 10⁻⁶ DALY/person/year = loss of 365 healthy days/one
million/year = 1 excess case of cancer/100000 people
drinking water over 70 years
Target Pathogens Selected
 Bacteria - Campylobacter jejuni
 Virus – Rotavirus
 Protozoa - Cryptosporidium
Tiers presented
 Highly Protective ----- 10⁻⁶ DALY /person/year
 Protective -------------- 10⁻⁴ DALY/person/year
 Interim ----------------- Achieves “protective” targets for
two classes of pathogens & results in health gains in
applications.
Health Based HWT Performance
Targets
Target
Log reduction -
Log reduction -
Log Reduction -
Bacteria
Virus
Protozoa
Highly Protective
≥4
≥5
≥4
Protective
≥2
≥3
≥2
Interim
Achieves “protective” targets for two classes of pathogens &
results in health gains
Derivation of Targets using QMRA
 Based on known sets of data and several assumptions
 Pathogens selected had been cited in GDWQ of WHO
along with being involved in several outbreaks
 Pathogen levels in raw water calculated on the basis of
adding wastewater to a concentration of 0.01%
 Daily water consumption, probability of infection by
each pathogen, risk of diarrheal illness, and
susceptible population were all assumed for the
calculations of the DALY and thus these target levels
Technologies described in
Appendices
 Chemical Disinfection (chlorine, bromine, iodine,
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chlorine dioxide, ozone, etc.
Filters of all types (Membrane, ceramic, Granular, etc)
Solar Disinfection
UV
Thermal Technologies
Coagulation, precipitation and settling
Combination of relevant technologies
Protocol Details
 Two types of test waters similar to EPA protocol
 Differentiation of protocols based on technology
 Alternate indicator microbes suggested (E. coli, MS2, C.
perfringens spores, inert particles, etc.)
 But not very detailed directions for carrying out the actual
tests with the selected pathogens or suggested alternates
 Mostly guidelines for development of national regulations
and protocols along with certification approaches
Potentially Simpler Approach
 Present approach for interim targets appears well thought out and
appropriate compared to earlier 1/1/1 log reductions proposed.
 Had to make several assumptions to reach these two tiers and targets.
Any different assumptions would have lead to very different results
 Could have decided on ONE suggested goal to be reached by different
countries.
 10⁻⁵ DALY/person/year could have been selected as the only one
approach
 This approach would have lead to targets of 3/4/3 for bacteria/virus/
protozoa. If one gets 4 logs of virus reduction along with 3 logs of
protozoan reduction that technology would have easily also achieved 6
logs or more of bacteria reduction. Same as EPA protocol of 6/4/3!!!