Comparing Wastewater-Based and Case-Based <i> R _t </i> 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 complementary surveillance approach 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 ( ) of SARS-CoV-2 in Georgia, USA.We used a Generalised Linear Mixed Model to analyse viral concentration data from multiple wastewater treatment plants (WWTPs) collected between June 1, 2022 and December 15, 2022.After controlling for flow rates and site-level heterogeneity, model residuals were transformed into a nonnegative incidence-like series used to estimate wastewater-based .Wastewaterbased was compared with case-based estimates using Spearman correlation.The two estimates showed concordant temporal patterns across most sites, with stronger correlations in areas with higher case counts (Spearman correlations ranging from 0.34 to 0.82, < 0.001).Wastewater-based tracked increases and decreases in transmission over similar time scales as case-based estimates, while exhibiting reduced sensitivity to short-term changes in clinical testing and reporting behaviour.These findings suggest that WBE can support estimation of transmission trends and complement traditional case-based surveillance for public health monitoring.