Wastewater Surveillance Uncovered the Impacts of the Timing of COVID-19 on the Epidemic Trajectories of Other Respiratory Diseases in Two Northeastern Cities in China

In this study, we conducted quantitative polymerase chain reaction (qPCR)-based wastewater surveillance for 12 prominent respiratory pathogens in two northeastern cities of China, Dalian, and Benxi, to understand the cocirculation patterns between COVID-19 and other respiratory diseases from October 2022 to July 2023. Wastewater surveillance revealed that Influenza A virus (IAV) and respiratory syncytial virus (RSV) sewage concentrations exhibited an upward trend from October 2022 in both cities but with distinct epidemic trajectories. In Dalian, IAV and RSV sewage concentrations both peaked in early December, followed by a rapid decline since the emergence of COVID-19 on November 23, 2022. In Benxi, two bell-shaped curves were observed for IAV and RSV sewage concentrations, both peaking in mid-December of 2022, even though severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in wastewater on December 8, 2022. After a rapid decline in SARS-CoV-2 sewage concentrations in January 2023, a new wave of IAV in wastewater occurred between February and early April in both cities, followed by a surge of SARS-CoV-2 RNA in early May. Meanwhile, an out-of-season epidemic of RSV from March to May was observed in Benxi based on the cities' sewage concentrations. This study highlights the impact of the timing of COVID-19 on the epidemic trajectories of other respiratory diseases.