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Quantitative Microbial Risk Assessment
Transcript of Quantitative Microbial Risk Assessment
• The Clean Water Act relates to the protection of
source water for drinking water systems
• QMRA model takes into account the different
pathogens present in source water
• Different water sources have different microbial
risks associated with them
• Ground water sources having risks - from bacteria
• Surface water has risks - from protozoa in addition
to viruses and bacteria.
Quantitative Microbial Risk Assessment
Canadian Drinking Water Guidelines 1
What is Quantitative Microbial Risk Assessment ?
A mathematical risk assessment framework that uses information about a microbial pathogen to quantify the risk of infection for that specific pathogen
With relation to Drinking Water, the QMRA model is used to quantify the risk of infection from consuming treated drinking water
Applied on a case by case basis to a specific drinking water system (Source- Treatment-Tap)
Uses the World Health Organization’s Disability Adjusted Life Years (DALY) model to quantify the risk associated with a particular pathogen in terms of time lost per year/person due to infection from that pathogen
The Canadian Drinking Water Quality Guidelines, a document produced by the federal government, states that the acceptable DALY from a QMRA should be below 10-6 years/person for pathogens in drinking water.
The Microbial Substances of Concern
There are 3 kinds of waterborne pathogens: Bacteria, Protozoa and Viruses
• Bacteria include E. coli and total coliforms
• Protozoa include Giardia and Cryptosporidium
• Viruses include enteric Viruses like Hepatitis and Norovirus, Viral diversity is staggering compared to bacteria and protozoa
What are the Components of QMRA?
A QMRA can be broken down into 5 sub categories:
• First step of any QMRA: Know thy Enemy
• Identify what pathogen(s) are the focus of the
• Identify what human diseases are associated with the
pathogen in question
• Examine different characteristics about the pathogen, such as : Fatality Rates, Method of Infection, Latency, Incubation Times, Duration of Disease, Symptomology and Excretion Rates
• Uses the “Dose” of pathogen received for calculation
• Mathematical models for infectivity rates obtained from animal studies or human outbreaks if available
• Uses Dose Amount information from the Exposure Assessment in the mathematical models
• Uses mathematical models to assess the risk of infection from a particular pathogen
• Exposure is the physical contact between
pathogen and an individual
• Relates how the pathogen gets from its source
(sewage, infected individual, contaminated well) to
• Factors in the effectiveness of a water treatment
facility before producing a Dose amount to be
used in the Dose response
• Takes the Dose Amount from the Exposure Assessment and the
probability of infection from the Dose Response to produce an overall
risk of infection.
• Basic model:
Risk = Dose Amount x Probability of Infection
• Produces a DALY amount that can be compared against the Canadian
Drinking Water Quality Guidelines value of 10-6 associated with that
particular pathogen in that particular drinking water system
years/person to determine the risk of infection
• Takes into consideration all of the
previous steps to develop control
measures to prevent infection from
consuming treated drinking water
• Examples of control measures are
filtration, UV disinfection,
membrane technology, chlorination
• What is QMRA and how does it relate to drinking
• Where is QMRA used in Ontario.
• Gap analysis Between provincial and federal
regulations and guidelines.
• Recommendation’s for an improved QMRA model.
• Recommendations for future Legislation.
Different models of QMRA
• Old model of QMRA
• Effects of Old Model
• Recommendations to
different QMRA model
• Relation between WHO
• Regulations posted by WHO
• Advantages of QMRA:
1. Ability of comparing risks
2. The transparency
3. The potentiality
4. Removal of hidden
• Adopting QMRA model
• Benefits of QMRA model
• Follow Guideline for
Canadian Drinking Water
Clean Water Act
• These risks are heightened by the presence of
what the Clean Water Act calls “drinking water
threats” In the context of QMRA
• Sources of microbial contamination - which include
sewage treatment (or anywhere sewage is
• Application of agricultural source material (manure)
and locations where livestock are held
• Identification of threats to source water can aid in the Hazard Identification part of QMRA
Canadian Drinking Water Guidelines 11
• QMRA to examine and quantify the
risk of infection with regards to
drinking treated water.
• It recommends source water
quality to determine the level and
present of :
Escherichia coil (E.coli)
Health Protection and Promotion Act
• Small drinking water systems in Ontario are under
the supervision of the Ministry of Health and Long
• These small drinking water systems (SMWS)
undergo a risk assessment by a Ministry of Health
representative to identify microbiological threats
that apply to the system
• A Risk Categorization (RCAT) program has been
developed by the Ministry to assess small drinking
• On a case by case basis to assign a risk level of
low, medium or high to each system
• This information is used through QMRA to
determine the infection level of the system
• This document showcases the federal government’s
recommendations for drinking water treatment in Canada
• Water supply and distribution system comes under Provincial
• Federal government does not directly create or enforce any
legislation as it relates to provincial Government system
• But, rather propose guidelines as to how drinking water
should be treated
The Use of QMRA on a Provincial and Municipal Level
Used by provinces across Canada, including Alberta and Ontario.
Used by several municipalities in Ontario to assess the effectiveness of their multibarrier approach to achieve Health Canada's goals of reducing the risk of enteric viruses
How does QMRA Apply to the Water Treatment Process?
Health Canada's goal is to have a 4-log reduction
A 4-log reduction needs to be monitored every 15 minutes