Quantitative Microbial Risk Assessment

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Quantitative Microbial Risk Assessment

QMRA – quantitative microbial risk assessment – is the technique of estimating the public health risk due to exposure to pathogenic micro-organisms, such as bacteria, protozoans and viruses that may be present in recreational/drinking water. Based on mathematical dose-response models and making use of specialist microbiology knowledge, we have developed and applied QMRA for a variety of waterways receiving wastewater discharges in New Zealand. 


We have successfully used QMRA to:

  • determine levels and types of wastewater treatment needed to reduce swimming and shellfish-harvesting health risk to acceptable level.

  • determine risk to population to present case for investing in network upgrades that aim to reduce wastewater overflow.

QMRA can also: 

  • Assist resource planners and policy decision-makers to generate, evaluate and compare risk profiles under different management scenarios, such as different levels and types of treatment in a wastewater treatment plant (WWTP),

  • Help to investigate many different scenarios of inffluent/effluent quality and environmental condition (e.g., rainfall, wind, el-nino/nina, daylight UV-based inactivation etc) which otherwise might not be readily encountered in field-based risk assessments.

  • Help to assess risks associated with extreme events (such as periods of infectious outbreaks in the community or following breakdown of equipment resulting in treatment bypass) in a way that gives effect to the Resource Management Act.

  • Help to isolate the effect of wastewater being discharge being studied from all other possible sources of contamination

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