Long-Term Dynamics of Pediatric Respiratory Pathogens Before, During, and After the COVID-19 Pandemic: Evidence From Nine Years of Surveillance in the Netherlands (2015-2023).

Respiratory tract infections (RTIs) are common in children and are caused by viral and bacterial pathogens. However, seasonal variability and limited age-specific data obscure a clear understanding of their epidemiology and clinical outcomes. The annual incidence of respiratory pathogens, co-infections, and disease burden was retrospectively investigated. Clinical data and respiratory swabs were collected from children < 18 years who presented with respiratory symptoms at a Dutch Emergency Room between 2015 and 2023. Swabs were tested for 20 common pathogens using MLPA technology. In total, 3575 samples were collected from 2969 children. 74% of swabs were positive for at least one pathogen. Rhinovirus (RV: 36.8%), respiratory syncytial virus (RSV: 19.5%), and adenovirus (5.3%) were detected most often. Pathogen co-detections occurred in 20.8% of all positive samples, with the combination RV-bocavirus (3.6%) being the most common. In < 12-month-olds, the need for hospitalization was associated with RV (84%), RSV (84%), or influenza (80%). After adjusting for covariates, the need for respiratory support was associated with infections caused by human metapneumovirus and RSV. Interestingly, Mycoplasma pneumoniae was circulating year-round and almost exclusively identified in children over 2 years of age, of whom most required hospitalization (81%), respiratory support (60%), and antibiotics (89%). Longitudinal data collected over nearly a decade provided insights into the seasonality and burden of respiratory pathogens in children. RSV burden remains high, especially in infants < 6 months, whereas M. pneumoniae infections are common, especially in children > 2 years. These results may inform current diagnostic guidelines and suggest age-specific adaptations and monitoring.