Comparing Wastewater-Based and Case-Based Rt Estimates of SARS-CoV-2 Transmission in Georgia Using Generalized Linear Mixed Models

The COVID-19 pandemic has highlighted limitations in case-based surveillance due to inconsistent testing and reporting. Wastewater-based epidemiology (WBE) has emerged as a promising alternative for tracking SARS-CoV-2 transmission, capturing both symptomatic and asymptomatic infections. The aim of this study is to evaluate the effectiveness of WBE in estimating the effective reproduction number (Rt) of SARS-CoV-2 in Georgia. We used a Generalized Linear Mixed Model to analyze viral concentration data from multiple wastewater treatment plants (WWTPs) collected between June 1, 2022 and December 15, 2022. After controlling for flow rates and other spatiotemporal differences between the plants, residuals from the model were used to estimate wastewater-based Rt. It then was compared to case-based Rt estimates using Spearman correlations. The two Rt estimates generally aligned across most sites, with stronger correlations in areas with higher case counts (Spearman correlations ranging from 0.29 to 0.88, p < 0.001). The two estimates reflected the increases and decreases in transmission within two weeks of each other with wastewater being a potentially more sensitive surveillance instrument for transmission trend. These findings suggest that WBE is a reliable tool for estimating SARS-CoV-2 transmissibility and can complement traditional surveillance methods for a more comprehensive public health response.