(J-384) SARS-CoV-2 Wastewater Concentration and Public Health Metric Correlation Analysis for Washington County Oregon

Wastewater-based epidemiology (WBE) can serve as a monitoring tool that provides valuable information on the overall health status of a community and can help inform public health policies and interventions. WBE is not affected by sampling bias or exhaustion from repeated sampling and is cost-effective compared to individual clinical testing surveillance. Clean Water Services operates four water resource recovery facilities (Durham, Forest Grove, Hillsboro and Rock Creek) that collect and treat wastewater from over 95% of residents of Washington County, Oregon. Clean Water Services began its wastewater surveillance program in the Spring of 2020 in collaboration with Oregon State University (OSU) and later with OSU and the Oregon Health Authority as a part of a state-wide wastewater surveillance network. The wastewater surveillance program at Clean Water Services includes quantifying the wastewater SARS-CoV-2 concentrations and identifying the SARS-CoV-2 variants present.  This study investigated the ability of WBE to estimate public health metrics at the county level.

Reverse transcriptase droplet digital PCR (RT-ddPCR) was used to quantify the SARS-CoV-2 viral concentration from 24-hr composite wastewater samples collected at the influent of each of the four facilities. Samples with SARS-CoV-2 concentrations greater than 4.0 Log₁₀ gc/L were sequenced to identify variants using multi-locus sequence typing approach. Population-weighted averages of wastewater SARS-CoV-2 concentrations were correlated to public health metrics of clinal cases, test positivity, vaccinations, hospitalizations, and deaths for Washington County over last 2.5 years. Data analysis was performed by building linear regression and statistical models in Python between the two quantitative variables.

Correlation analysis revealed a strong positive correlation between wastewater SARS-CoV-2 concentrations and 7 day rolling averages of the clinical cases (r =0.75), hospitalizations (r = 0.73) and positivity (r = 0.66). A weak positive correlation was observed between death counts (r = 0.12) and wastewater data. Higher vaccination rates in the face of emerging variants have contributed to a decrease in the severity of the disease, as evidenced by lower hospitalization .

There was a strong correlation between the emergence of new variants observed in the wastewater and clinical data. This suggests that wastewater surveillance can function as an early detection system, alerting public health authorities to the emergence and spread of new variants. 

Examination of multiple facilities in Washington County illustrated the similarity of the correlation between the weighted average of the four facilities and individual facilities with county-wide public health metrics. This result may indicate that monitoring carefully selected sentinel cities can provide information regarding a larger geographic area.

The findings of this study highlight the potential of WBE as a tool for public health monitoring. Positive correlations among various clinical and wastewater data has demonstrated that WBE can provide public health officials with an additional data stream in framing health policies aimed at preventing and controlling infectious diseases.