Review Reports

Round 1

Reviewer 1 Report

The main objective of the presented research was to determine the minimum concentration of free chlorine to the concentration of CYA based on the risk of gastrointestinal disease due to the accumulation of selected pathogens in the faeces. An additional goal was to set a simple rule regarding FC to CYA ratio in order to achieve consistent and effective disinfection. To achieve this aim, the authors developed a model that takes into account the rate of introduction of pathogens into the pool water, disinfection, turbulent diffusion transport, and the uptake of pathogens by swimmers in order to calculate the associated risk of disease.

Finally, the authors found that FC and CYA concentrations in pools should be jointly regulated as a ratio. Based on the obtained results, they recommend that the maximum CYA / FC ratio should be 20.

I want to emphasize three positive features of this article:

·  A wide literature and data (Supplementary Material) review from 1943 to 2019.

·  Analysis, evaluation and references to the effect of cyanuric acid (CYA) on many species of microorganisms (bacteria, protozoa, viruses, algae and amoeba) and the risk of infections of them.

· Detailed model of validation of test results.

I suggest changing the title of the article to specify who may be at risk of gastrointestinal disease (not in swimming pools but in swimmers (?)).

I have no doubt that the risk model presented by the authors can be very important for the practice of chlorination of swimming pool water to protect public health.

However, I have a question:

Considering that the concentration of CYA <100 mg/L, and the concentration of FC = 0.3-1.0 mg/L (in most regulations regarding the quality of swimming pool water) - Is the recommended ratio CYA/FC = 20 not a challenge impossible to achieve in today’s  swimming pool water treatment systems? 

Please reply and supplement any conclusions in this regard.

Author Response

Please see uploaded Word file for our reply.

Author Response File: Author Response.docx

Reviewer 2 Report

The study aims to assess the Impact of Cyanuric Acid on Risk of Gastrointestinal Illness at Swimming Pools. The major focus of the paper is the effect of CYA/FC ratio on annual probability of infection. Overall the goal of this paper is to assess the impact of CYA application in chlorinated swimming pools on swimmer AGI risk.

The research is appropriate, and very timely. Methods and results are clearly presented. The research could be very useful from public health prospective. For this reason, the manuscript can be considered suitable for publication after minor revisions.

In particular, the logic model described few major mechanisms of free chlorine binding with CYA but it may contain more processes. Method section can be improved by strengthening logic model with assumptions. Manuscript builds on the well-established methods and clearly adds to current body of knowledge. Additional references to more recent studies in this area would be highly beneficial.

Number of tables in the manuscript can be reduced by explaining the presented information in the text.

I hope that the Authors will make revisions as I believe this manuscript would be well received by the academic community.

Author Response

Please see uploaded Word file for our reply.

Author Response File: Author Response.docx