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Cyanuric Acid use CMAHC Ad Hoc Committee Report

Cyanuric Acid use CMAHC Ad Hoc Committee Report
Friday, October 18, 2019
1:30 pm–2:20 pm
MAHC Track

In 2017, the CMAHC Cyanuric Acid (CyA) Ad Hoc Committee reported on the ongoing development of a model for calculating the relative risk to bathers from varying CyA concentrations. Here the committee presents the model and the committee conclusions. Information will be given on how to download the model and work with it to calculate relative gastrointestinal risk for individual scenarios. The flexibility, uses, assumptions, and limitations of the model will also be discussed. For example, in addition to investigating the effect of CyA, relative risk can be calculated to help inform a risk assessment for the following scenarios:

  • How risk changes with bather load and venue type
  • The effects of secondary disinfection (e.g. UV, ozone) and filtration (with and without coagulants) on risk
  • How distance from an infected shedding bather affects risk and how this differs for different pathogens
  • Steady-state diurnal recovery for Giardia and the morning vs. afternoon differential risk
  • Single high-shedder relative risk
  • Relative risk from one bather swimming behind another
  • How risk can vary with bather cleanliness (e.g. shower, toilet hygiene)
  • How water temperature affects risk

Absolute risk is difficult to determine due to the huge variation in possible input parameters. The model can, however, be used to estimate relative risk given a set of assumptions.  Even with this caveat, the committee believes that public health authorities may be able to use this model to help prioritize and develop potential code changes that will have the most impact on public health.