Purpose of this study is to evaluate clinical, humanistic and health economic burden of Respiratory Syncytial Virus (RSV) in infants born 29 to 35 Weeks Gestational Age (wGA) hospitalized for RSV at up to 12 months of age.

This surveillance study will enroll approximately 500 eligible infants from approximately 40 study sites in the US, hospitalized for laboratory-confirmed, nosocomial or community-acquired RSV disease during the study eligibility period of 1 October 2014 through 30 April 2015 (Season 1) and 1 October 2015 through 30 April 2016 (Season 2). During these eligibility periods, infants may be enrolled:

• Prospectively at the time of their index Respiratory Syncytial Virus Hospitalization (RSVH) admission or any time prior to their index RSVH discharge, or
• Retrospectively on the basis of electronic medical record (EMR) review following discharge from the index RSVH.

Regardless of the timing of study enrollment (i.e., in relation to the date of discharge from the index RSVH), sites will identify all infants eligible for study participation, including those treated in the inpatient ward and intensive care unit (ICU). Identification of all potentially eligible infants will be ensured through the review of the EMR, or other local healthcare database deemed appropriate for study purposes by the Study Coordinating Center (SCC).

The clinical, humanistic and health economic outcomes associated with the RSV disease will be characterized in the outpatient and inpatient settings, from the onset of symptoms of RSV disease pre index RSVH to up to 4 months post index RSVH discharge date (additionally to 12 months post index RSVH discharge date in Season 1 only), on the basis of medical records and Parent/Guardian self-report. Information regarding any sequelae associated with the index RSVH, medically-attended wheezing episodes, loss of work productivity and healthcare resource utilization (HRU) related to the management of RSV-related disease will also be collected from the medical records and Parent/Guardian by telephone interview at approximately 1 month and 4 months following discharge from the index RSVH (additionally at 12 months in Season 1 only).

Inclusion Criteria:

• Born at 29 to 35 wGA (i.e., 29 weeks, 0 days through 35 weeks, 6 days)
• Laboratory-confirmed, nosocomial or community-acquired RSV disease (RSV can be documented in the outpatient and/or inpatient setting during the illness that resulted in the index hospitalization)
• Hospitalized ≥24 hours for the diagnosed RSV disease (the index RSVH)
• <12 months of age at time of index RSVH admission
• Written informed consent and any locally required authorization (e.g., HIPAA), obtained from the infant's Parent/Guardian

Exclusion Criteria:

- Receipt of RSV immunoprophylaxis within the 35 days prior to onset of respiratory symptoms associated with the index RSVH

Infants born at 29 to 35 wGA not receiving RSV prophylaxis hospitalized for RSV at less than 12 months of age