Respiratory syncytial virus (RSV) is a leading cause of acute lower respiratory tract infection in infants and young children and contributes substantially to pediatric emergency department (ED) visits and hospitalizations. In Türkiye, nationally representative prospective data describing the epidemiology, clinical spectrum, and resource utilization of RSV-positive children presenting to pediatric EDs remain limited. This multicenter prospective observational study aims to characterize demographic and clinical features of RSV-positive children under 5 years of age presenting to participating pediatric EDs across two consecutive RSV seasons, and to quantify key healthcare utilization outcomes, including ED observation duration, hospitalization, and intensive care unit (ICU) admission.

This is a multicenter, prospective observational cohort study conducted in pediatric emergency departments in Türkiye over a consecutive RSV season. Eligible participants are children younger than 5 years who present to a participating pediatric ED with at least one compatible clinical diagnosis and have RSV infection confirmed by a nasopharyngeal sample using either a rapid antigen test or PCR, based on local site capacity. Written informed consent will be obtained from a parent or legal guardian prior to study procedures.

Standardized case report forms will be used to collect demographics (age, sex, region, socioeconomic indicators), relevant risk factors (e.g., prematurity, congenital heart disease, chronic lung disease, passive smoke exposure, breastfeeding status), presenting symptoms, vital signs and physical examination findings, diagnostic evaluations (radiology and laboratory results as available), and clinical management and outcomes. Outcomes of interest include ED observation duration, disposition (discharge vs hospitalization), ICU admission, and, when applicable, the need for oxygen or ventilatory support. Data will be entered into a secure centralized database. The study will evaluate seasonal and regional patterns and will explore predictors of severe outcomes among RSV-positive children using multivariable models.

Inclusion Criteria:

• Age <5 years at presentation
• Presentation during RSV season (2025-2026 )
• RSV infection confirmed from a nasopharyngeal sample by rapid antigen test or PCR according to site capacity
• Presentation to a participating pediatric ED with at least one of the following clinical diagnoses: upper respiratory tract infection, bronchiolitis, pneumonia, apnea, seizure/convulsion, or myocarditis
• Written informed consent obtained from a parent or legal guardian.

Exclusion Criteria:

• Parent or legal guardian declines consent

The study population consists of children aged <5 years presenting to participating pediatric emergency departments in Türkiye during consecutive RSV season (2025-2026 ) who have respiratory syncytial virus (RSV) infection confirmed from a nasopharyngeal specimen using rapid antigen testing and/or PCR according to local site capacity and standard clinical practice. Eligible participants include RSV-positive children evaluated for compatible clinical diagnoses at presentation (e.g., upper respiratory tract infection, bronchiolitis, pneumonia, apnea, seizure/convulsion, or myocarditis). Enrollment requires written informed consent from a parent or legal guardian; children are excluded only if consent is declined. Clinical management is not assigned by the protocol and follows routine care; participants are observed for outcomes during the index emergency department encounter and, when applicable, through the index hospitalization.

Individual participant data (IPD) will not be shared because the study was not designed with an IPD-sharing plan in place, and the current ethics approvals and informed consent documents do not include provisions for public IPD sharing.