Simplified linear dose-response models for low-dose QMRAs

Protecting public health is at the center of potable reuse planning. Utilities use multiple treatment processes to remove disease-causing microorganisms, but determining how much treatment is needed requires understanding and quantifying potential health risks.

Quantitative microbial risk assessment (QMRA) helps utilities and regulators make those decisions. However, the mathematical models behind these assessments can be complex and difficult for non-specialists to apply.

A recent peer-reviewed study published in AWWA Water Science, “Simplified Linear Dose-Response Models for Low-Dose QMRAs,” co-authored by Carollo’s Emily Clements, explores whether these models can be simplified for the extremely low pathogen concentrations relevant to potable reuse.

Simplifying Quantitative Microbial Risk Assessment

An important part of QMRA is the dose-response model, which estimates the relationship between exposure to a pathogen and the probability of infection. These calculations help establish pathogen-reduction requirements for potable reuse treatment systems, often expressed as log-reduction values (LRVs).

The researchers examined commonly used models for norovirus, adenovirus, enterovirus, Cryptosporidium, and Giardia. They found that at the low pathogen concentrations relevant to drinking water and potable reuse, these complex models can be represented using much simpler linear equations.

This means calculations could be performed using familiar tools such as Excel rather than requiring specialized coding or statistical software, making QMRA more accessible and easier to interpret.

Connecting Pathogen Reduction to Public Health Risk

The simplified models also revealed a clear relationship between treatment performance and estimated infection risk.

Within the ranges studied, each additional 1-log reduction in pathogen concentration corresponded to approximately a tenfold reduction in estimated risk. This provides a straightforward way to understand how adding treatment barriers or adjusting operating conditions can affect microbial risk.

The researchers also found relatively consistent differences among dose-response models for individual pathogens, which could simplify comparisons between models.

Making Potable Reuse Risk Assessment More Accessible

Simplifying these models does not replace rigorous microbial risk assessment. Instead, it can make the underlying calculations more transparent and accessible to utilities, regulators, engineers, and other decision-makers.

As potable reuse continues to expand, approaches like these can help reduce technical barriers, improve communication, and support more consistent, risk-informed treatment decisions.

Read the full study in AWWA Water Science to learn more about simplified dose-response models and their potential applications for potable reuse QMRA.