Epidemiology of SARS-CoV-2, Influenza, RSV, and Human Metapneumovirus Across the COVID-19 Era: An Eight-Year Tertiary-Center Study in Saudi Arabia.

BACKGROUND: Respiratory tract infections (RTIs) caused by viruses are a public health problem, contributing to hospital admissions and morbidity worldwide. The COVID-19 pandemic substantially altered the detection patterns of respiratory viruses through public health interventions. Longitudinal data on these changes and viral seasonality remain limited in Saudi Arabia. This eight-year study evaluated epidemiological and seasonal patterns of major respiratory viruses across the COVID-19 era at a major Saudi tertiary care center. METHODS: A retrospective observational study was conducted at King Khalid University Hospital, Riyadh, from October 2017 to December 2025. PCR-confirmed detections for SARS-CoV-2, Influenza A, Influenza B, respiratory syncytial virus (RSV), and human metapneumovirus (HMPV) were extracted from the hospital Laboratory Information System. Demographics, co-detection, seasonality, and length of stay (LOS) were analyzed across four eras spanning the pre-COVID-19, lockdown, restriction, and post-restriction periods using descriptive statistics, the Kruskal-Wallis test, and multivariable negative binomial regression. RESULTS: Among 5708 confirmed respiratory viral detection episodes, SARS-CoV-2 was the most frequently detected (52.5%), followed by Influenza A (19.1%), RSV (16.4%), Influenza B (8.4%), and HMPV (3.6%). Before the pandemic, Influenza A accounted for the largest proportion of detected episodes (71.1%), with detections clustering particularly during autumn and winter seasons, whereas SARS-CoV-2 accounted for the majority of detected episodes during the lockdown and restriction eras (97.4% and 93.2%). The post-restriction era became more diverse, with RSV being detected in substantial proportions (28.3%), showing prominent winter activity. RSV and HMPV predominantly affected children aged 0-5 years, whereas SARS-CoV-2 was more frequently detected among older adults. Among adults, older age was associated with prolonged LOS; Influenza A and HMPV were associated with shorter stays compared to SARS-CoV-2. Among children, no virus was independently associated with LOS after adjustment for age and sex; however, older age was associated with longer hospital stays. CONCLUSION: The observed detection patterns of major respiratory viruses shifted substantially across the COVID-19 eras, with notable post-restriction diversification among observed positive detections. LOS was associated with age in both adults and children and with virus type among adults, supporting continued surveillance to guide preventive and clinical strategies.