Review 1: "Assessing Health Equity in Wastewater Monitoring Programs: Differences in the Demographics and Social Vulnerability of Sewered and Unsewered Populations Across North Carolina"

Ivan Ramirez

doi:doi:10.1162/2e3983f5.e76875db

Assessing health equity in wastewater monitoring programs: Differences in the demographics and social vulnerability of sewered and unsewered populations across North Carolina

by Xindi C. Hu, Stacie K. Reckling, and Aparna Keshaviah

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Published on Oct 07, 2023
www.medrxiv.org

Description

Abstract Background Wastewater monitoring is a valuable tool to track community-level disease trends. However, the extent to which vulnerable populations have been included in statewide wastewater monitoring programs remains unstudied.Objectives We conducted a geospatial analysis to examine (1) the representativeness of wastewater data collected through the North Carolina Wastewater Monitoring Network as of June 2022, and (2) the potential of wastewater data to generalize to unsewered populations in the county.Methods After intersecting wastewater treatment plant (WWTP) service areas (sewersheds) with census block and tract boundaries for 38 WWTPs across 18 counties, we compared the demographics and social vulnerability of (1) people residing in sewersheds of monitored WWTPs with countywide and statewide populations, and (2) people connected to any sewer system—regardless of inclusion in wastewater monitoring—with unsewered populations. We flagged differences greater than +/-5 percentage points or percent (for categorical and continuous variables, respectively) and noted which were statistically significant (i.e., greater than twice the margin of error).Results As a whole, populations in monitored sewersheds resembled the statewide population on most demographics analyzed, with a few exceptions. When multiple WWTPs were monitored within a county, their combined service populations resembled the countywide population, although populations in individually monitored sewersheds sometimes differed from the countywide population. In nine counties for which we had comprehensive sewershed maps, we found that sewered residents had higher social vulnerability, a greater share of Hispanics and African Americans, lower income, and lower educational attainment than unsewered residents.Discussion Our results suggest that wastewater monitoring in North Carolina well represents the larger community. Ongoing analyses will be needed as sites are added or removed. The approach we present here can be used to ensure that wastewater surveillance programs nationwide are implemented in a manner that informs equitable public health decision-making.

RR:C19 Evidence Scale rating by reviewer:

Potentially informative. The main claims made are not strongly justified by the methods and data, but may yield some insight. The results and conclusions of the study may resemble those from the hypothetical ideal study, but there is substantial room for doubt. Decision-makers should consider this evidence only with a thorough understanding of its weaknesses, alongside other evidence and theory. Decision-makers should not consider this actionable, unless the weaknesses are clearly understood and there is other theory and evidence to further support it.

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Review: In this preprint, the authors claim that their findings indicate that wastewater monitoring in North Carolina well represents the larger community. Thus, they conclude that “wastewater data is capturing infections among groups that experienced more severe COVID-19 disease and higher mortality rates”.

Overall, this is an interesting study addressing questions related to wastewater monitoring and the social conditions and vulnerability of sewered and unsewered populations. The broader question is whether wastewater monitoring is reliable for disease surveillance among the larger community in North Carolina. The study is well designed, and the problem is clearly articulated; however, the conceptual/theoretical design is limited, including clarity about the domains chosen, and the results should be validated, even preliminarily. Furthermore, it was not clear why North Carolina was selected. This study will require moderate revision. Below are comments that will help improve the study.

Introduction:

The authors should define social vulnerability as it is mentioned in lines 67-69. There are bodies of literature that describe it, mostly from the disasters field (geography), and now adopted by public health, for example, the CDC.
In line 85, the authors should elaborate on why North Carolina was selected.

Methods:

In lines 119-121, the authors should describe which framework/model the conceptual domains are based upon. Social determinants of health, Social Vulnerability (CDC? Cutter et al.?) Why is social vulnerability a separate domain? The other four domains should make up social vulnerability. This should be clear, so the design and framework relate to a wider health geographic literature. Are you evaluating how individual variables compare to composite social vulnerability?
Additionally, the authors should explain why these variables are important. Are you correlating them with COVID-19? If so, refer to a few geographic studies. Social vulnerability’s relationship to health is complex and the most socially vulnerable areas are not always the worst affected by a health outcome. See COVID-19 studies below:
- Maroko, A.R., Nash, D. & Pavilonis, B.T. COVID-19 and Inequity: a Comparative Spatial Analysis of New York City and Chicago Hot Spots. J Urban Health 97, 461–470 (2020). https://doi.org/10.1007/s11524-020-00468-0
- Chen JT, Krieger N. Revealing the Unequal Burden of COVID-19 by Income, Race/Ethnicity, and Household Crowding: US County Versus Zip Code Analyses. J Public Health Manag Pract. 2021;27 Suppl 1, COVID-19 and Public Health: Looking Back, Moving Forward:S43-S56. doi:10.1097/PHH.0000000000001263
- Islam N, Lacey B, Shabnam S, et al. Social inequality and the syndemic of chronic disease and COVID-19: county-level analysis in the USA [published online ahead of print, 2021 Jan 5]. J Epidemiol Community Health. 2021;jech-2020-215626. doi:10.1136/jech-2020-215626
- Lee, J., & Ramírez, I.J. 2022. Geography of disparity: connecting COVID-19 vulnerability and social determinants of health in Colorado. Behavioral Medicine, 48, 72-84. https://pubmed.ncbi.nlm.nih.gov/35318900/

Can the authors provide maps of sewered versus unsewered population distribution?

Discussion:

In lines 243-246, how can these results be validated? It seems that the authors are prematurely concluding that “wastewater data is capturing infections among groups that experienced more severe COVID-19 disease and higher mortality rates”. Can the authors assess these assumptions with COVID-19? Pearson or Spearman correlation would be sufficient to explore this, although they would not capture spatial relationships without further geostatistical analyses.