Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript presents an important and well designed selection frame work, but it would be better if it shows the process of selection, actual outcomes of the selection process and a comparison between all sites vs reduced sites.

Author Response

The option of "shift and paste" was not working, therefore, plase check the attached doctument

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The paper proposes a criteria-based national down selection strategy for Germany AMELAG wastewater-based surveillance network, reducing approximately 170 wastewater sampling sites to 53 WWTPs for 2025 while aiming to preserve national SARS-CoV-2 trend monitoring. The method combines population coverage, federal-state representation, minimum technical/data quality criteria, strategic research priorities, and three historical SARS-CoV-2 performance metrics (RIIP, MAE, and proportion above LOQ). The main result is that the reduced network produced a national LOESS trend curve similar to the full network, with only slightly wider confidence bands.

The manuscript addresses the practically important and timely surveillance problem of how to maintain national WBS capacity after pandemic phase funding and sampling intensity decline. The proposed framework may be informative for other countries seeking efficient and sustainable surveillance designs. The topic fits the Microorganisms scope.

The study is grounded in an existing national program with real operational constraints, including federal governance, laboratory heterogeneity, and WWTP participation. The selection workflow is transparent at a high level and includes technical eligibility, minimum data quality, population coverage, strategic research sites, and statistical ranking criteria. The authors acknowledge key limitations, including urban bias, reduced rural information, laboratory heterogeneity, post-selection site changes, and SARS-CoV-2-specific ranking- The supplementary material provides a useful site inventory with selected 2025 sites, catchment populations, and comments on focus/supersite status.

Please add the study period, number of initial eligible WWTPs, final coverage, validation metrics, and limitations to the abstract section. Furthermore, avoid the unsupported implication that the design is already a “robust foundation” for future pathogen surveillance unless multi-pathogen validation is added.

The background is relevant but too descriptive. Consider to sharpen the knowledge gap. The manuscript is not simply about WBS value, but about principled network reduction under resource limitation. Add more engagement with optimization, equity, and post-pandemic surveillance sustainability literature.

The 15% state coverage target, 2% WWTP state population threshold, 90% industrial wastewater cutoff, and “two WWTPs per federal state” rule are policy relevant but not empirically justified with sensitivity analyses or formal objective functions. Please clarify.

Historical SARS-CoV-2 data are used both to select sites and to evaluate whether the reduced network reproduces the national trend. Consider a temporal holdout, leave-one-state-out validation, or prospective 2025 validation to strengthen the approach.

The Results state that the reduced and full curves were “nearly identical” and that confidence bands were on overage 7% wider. Please consider to report RMSE, MAE, correlation, concordance, peak-timing error, wave amplitude error, or predefined non-inferiority margin.

Consider to quantify representativeness beyond population coverage such as rural/urban, federal state, mobility/commuting, socioeconomic vulnerability, age structure, and geographic distance to nearest selected site.

The authors note that LOQ values vary by laboratory and method yet the proportion above LOQ remains part of site ranking. Please avoid using LOQ success as an unqualified data quality indicator.

The manuscript lists a GitHub link for data/code availability, but the link returned a 404/not found error when checked.

The Conclusions section is overly long and should be substantially condensed and rewritten to focus on the main findings, their practical implications, and the principal limitations. Several points currently repeat material from Results and Discussion and would be better removed or shortened.

English Language

Please revise the manuscript throughout for inconsistent singular/plural agreement, inconsistent capitalization, and mix procedural past tense with general present tense.

Figure 2: The legend and point categories are small and the cation is minimal. Please add state labels and clarify if point size reflects served population. The title appears to contain a typographical error “Selction”.

Update references to include international guidance, optimization frameworks, equity literature, and comparable national downscaling examples. Consider to add or more directly engage with (not limited to):

• WHO 2024 WES guidance because it provides a current international framework for prioritization, implementation, and integration of wastewater/environmental surveillance across one or more pathogens.
• Daza-Torres et al 2024 because it proposes an optimization framework integrating spatial distribution, population density, and social vulnerability.
• Lo/Eugene et al 2025 optimization study because it is a close comparator
• Benedetti et al 2024 Eurosurveillance survey because would contextualize Germany relative to other countries.
• CDC/NWSS program and site selection literature because it discusses program level surveillance objectives and national scaling experience.

Author Response

The option of "shift and paste" is not working, therefore, please see the attached document.

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The presented work is devoted to the development and justification of an approach to optimizing the network of wastewater-based surveillance sites in Germany. The authors propose a multi-stage sewage treatment plant selection system to maintain representative national monitoring of SARS-CoV-2 while significantly reducing the number of observation points. The work has a pronounced practical focus and addresses an urgent task for epidemiological surveillance systems — finding a balance between the sustainability of monitoring, data quality and resource constraints.

The strengths of the article include a well-structured research logic, a transparent description of the selection criteria, and reliance on real data from the national surveillance program. It is particularly important that the authors did not limit themselves to a theoretical description of the approach, but showed its applicability in practice: reducing the network to 53 WWTP did not lead to noticeable distortions of the aggregated national trend of SARS-CoV-2. This makes the work significant not only for Germany, but also for other countries considering scaling or optimizing similar systems.

It should also be appreciated that the authors honestly discuss the limitations of the proposed scheme. In particular, there is a shift towards large urban wastewater treatment plants, a lower representation of rural areas, as well as the dependence of statistical quality assessment primarily on historical data on SARS-CoV-2. This gives the work additional credibility and shows a mature approach to interpreting the results.

However, the article has some weak points. The main validation of the proposed approach is based on a comparison of national aggregated curves, while the issue of maintaining the sensitivity of the system to local outbreaks and regional peculiarities is less well-known. In addition, given the expansion of the tasks of wastewater surveillance to other pathogens and AMR, the use of predominantly SARS-CoV-2 as the basis for site ranking may limit the versatility of the proposed model in the future.

Overall, the work makes a positive impression. It is methodically consistent, practically significant, and fits well into the current challenges of developing sustainable epidemiological surveillance systems. The article deserves a positive review.

Recommendation - accept for publication after minor revision. It is advisable to strengthen the discussion of the limitations associated with multipath surveillance and the potential loss of sensitivity at the regional level.

Author Response

The option of "shift and paste" is not working, therfore, please see the attached document

 

Author Response File: Author Response.pdf