Seasonal Pattern and Age-Specific Detection of Eight Respiratory Viruses Causing Acute Respiratory Infection in 2024, Bangkok, Thailand

Since the emergence of COVID-19, the epidemiological and seasonal patterns of respiratory pathogens have shifted, highlighting the need for ongoing surveillance. This study investigated the epidemiology, seasonal trends, and age-specific detection of respiratory viruses among patients with acute respiratory infections (ARIs) in Thailand from January to December 2024. Eight respiratory viruses were detected using multiplex real-time RT-PCR. Of 7853 samples, 60.8% (4777) tested positive. The most frequently detected pathogens were influenza virus (IFV, 24.8%), SARS-CoV-2 (21.5%), and human rhinovirus (HRV, 20.8%). IFV showed biannual peaks during the cold and rainy seasons, SARS-CoV-2 peaked in the warm months, and HRV circulated year-round. Respiratory syncytial virus (RSV) and human metapneumovirus (HMPV) were primarily detected during the rainy season (July–November), reflecting a return toward pre–COVID-19 seasonal patterns. Age-specific differences were notable: HRV was most prevalent in children < 5 years, IFV predominated among those aged 6–18 years, and adults ≥ 19 years were mainly positive for IFV and SARS-CoV-2. Co-infections were most frequent in children aged 3–5 years, often involving HRV. These findings provide updated insights into post–COVID-19 viral epidemiology, emphasize the importance of age- and season-specific surveillance, and support the development of effective public health strategies for ARI control.