RESPIRIAMO – Italian hospital surveillance for lower respiratory tract infections: a multicenter retrospective cohort study of respiratory syncytial virus-associated hospitalizations in children under 2 years of age

Background: Lower respiratory tract infections (LRTIs) are a leading cause of hospitalization in infants, with respiratory syncytial virus (RSV) representing the most important etiologic agent in children under 2 years of age. Although RSV disease burden is well recognized, multicenter data describing hospitalization characteristics, severity, and risk profiles in Italian infants remain limited, particularly following changes in viral circulation patterns in recent years. The study was established to provide robust hospital-based surveillance data. This study aimed to describe the clinical features and the severity of RSV-associated LRTI hospitalizations in Italian children under 24 months, comparing RSV-positive and RSV-negative cases. Methods: The study included infants aged 0- < 24 months hospitalized for LRTI between the 2018/2019 and 2020/2021 seasons across 12 Italian pediatric centers. Demographic characteristics, medical history, clinical presentation, laboratory radiologic, and hospitalization data were collected. Patients underwent RSV testing on nasopharyngeal samples and were classified as RSV-positive or RSV-negative. Descriptive statistics and comparative analyses were performed using parametric or non-parametric tests. Results: One thousand five hundred forty-seven infants were included, out of which 1,263 (81.6%) were RSV-positive. RSV-positive infants were significantly younger than RSV-negative infants, more likely to be previously healthy and without a family history of atopy. RSV infection was associated with a more severe clinical course, higher rates of oxygen supplementation (67.6% vs. 39.1%), respiratory support, invasive ventilation, and intensive care unit admission (10.6% vs. 3.1%). Use of RSV prophylaxis (at that time, palivizumab) was rare in both groups. Conclusions: RSV was the predominant cause of LRTI and was associated with significantly greater disease severity. Most hospitalized infants were previously healthy, underscoring the need for preventive strategies targeting the general infant population.