A geospatial analysis comparing wastewater-monitored sewershed and statewide populations for 32 states participating...

Wastewater monitoring analyzes samples of untreated wastewater for pathogens to track community-level disease trends. A sewershed polygon helps define the sample population by depicting the community area that contributes sewage to the wastewater sample. This study utilized sewershed geospatial data submitted to the Centers for Disease Control and Prevention's National Wastewater Surveillance System (CDC NWSS) to determine the wastewater-monitored population characteristics and assess how well the wastewater-monitored population represents the broader population. In a geographic information system, we intersected sewershed, state, and county polygons with US Census data and social vulnerability data to calculate the proportion of the population with certain demographic and social vulnerability characteristics in each geographic unit. In 32 states, we compared the aggregated sewershed population within the state to the statewide population for wastewater monitoring sites sampling during the Fall of 2024. In four states, Colorado, New York, North Carolina, and Wisconsin, we further assessed wastewater representativeness; we compared the distributions of sewershed populations with county populations and examined how representativeness has changed across eight time points during 2021-2024. In Fall of 2024, CDC NWSS included sites in all 50 states covering 41% of the US population. In 5 of 32 states analyzed the wastewater-monitored population represented the statewide population across all variables except median household income. In 27 states, we observed that wastewater-monitored populations may over- or underrepresent certain populations based on factors like race and ethnicity, education, or social vulnerability. We found that over time, differences between sewershed and statewide population characteristics were only slightly affected by changes in the number of sampling sites and population. State and local health departments, as well as CDC NWSS, can utilize information about the wastewater sample population and how it compares to the state population to strengthen the use of wastewater monitoring data for public health action.