An Epidemiologic Surveillance Study Based on Wastewater and Respiratory Specimens Reveals Influenza A Virus Prevalence and Mutations in Taiyuan, China during 2023-2024

Background Influenza is a major cause of morbidity and mortality. We aim to use epidemiology based on wastewater and respiratory specimens to understand the occurrence of influenza A virus infections in Taiyuan city. Methods A retrospective epidemiology surveillance was carried out at a designated hospital and five wastewater treatment plants in Taiyuan city from 2023 to 2024. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was used to detect influenza A viruses in wastewater and respiratory specimens. Whole genome sequencing was performed on 17 influenza strains obtained in this study, and subsequent analyses included characterization, phylogenetic construction, mutation analysis, and nucleotide diversity assessment. Results A total of 520 wastewater samples and 1,203 throat swab samples were collected. We detected RNA concentration from pH1N1 and H3N2 viruses in wastewater and got 17 genome sequences (5 of pH1N1 and 12 of H3N2) in respiratory specimens. Whole-genome sequencing showed co-prevalence of pH1N1 viruses in the branches of 6B.1A.5a.2a.1 and H3N2 viruses in the branches of 3C.2a1b.2a.2a.3a.a in Taiyuan from 2023 to 2024. Moreover, a HA mutation (N138D), predicted to be of high phenotypic consequence, was found in 8 Taiyuan H3N2 sequences. Conclusion This study highlights the predominant presence of pH1N1 and H3N2 strains in Taiyuan. The analysis also identified amino acid site variations in the antigenic epitopes, contributing to immune escape.