Epidemiology of severe acute respiratory infections in South Korea: a nationwide surveillance study

BACKGROUND: Severe acute respiratory infections (SARIs) are a critical public health concern due to their substantial morbidity and mortality rates across age groups. The objective of this study was to investigate the epidemiological characteristics, pathogen distribution, and clinical outcomes of SARIs in South Korea by analyzing nationwide surveillance data. METHODS: We conducted a prospective, multicenter surveillance study from January 2017 to January 2023 across sentinel hospitals nationwide, coordinated by the Korea Disease Control and Prevention Agency (KDCA). Respiratory specimens were collected and tested for a panel of viral and bacterial pathogens. Clinical data and outcomes were analyzed according to pathogen detection status. RESULTS: A total of 47,857 hospitalized patients with SARIs were enrolled based on standardized criteria: fever (≥ 38 °C), cough, and symptom onset within 10 days prior to hospitalization. Pathogens were identified in 52.5% of enrolled patients. The group that tested positive for pathogens was significantly younger (median age of 4.0 years) than the group that tested negative (median age of 59.0 years). Viral pathogens were more prevalent in children, whereas bacterial pathogens, such as Streptococcus pneumoniae, were more prevalent in older adults. Seasonal trends were observed: influenza and respiratory syncytial virus (RSV) peaked in winter; rhinovirus circulated year-round; and SARS-CoV-2 showed irregular peaks. Patients with confirmed pathogens had higher rates of pneumonia and mortality, as well as longer hospital stays (P < 0.001), compared to patients without confirmed pathogens. Antivirals were more commonly used in the pathogen-positive group, while antibiotics were predominantly prescribed to patients without confirmed pathogens. Geographic and sex-specific variations in pathogen distribution were also identified. CONCLUSIONS: This study provides a thorough examination of the epidemiology of SARIs in South Korea over a six-year period. The findings reveal notable differences in pathogen prevalence and related clinical outcomes by age, season, and region. These results underscore the importance of sustained nationwide surveillance and the development of targeted, seasonally adaptive public health strategies to mitigate the impact of SARIs on vulnerable populations.