Study samples
The study include archived nasopharyngeal swab (NPS) and oropharyngeal swab (OPS) samples of the RITM-PNIC in Muntinlupa City, Philippines. Samples were selected systematically with the number of samples from each site proportionate to the number of samples collected from children age (<5y) with influenza-like illness (ILI) or severe acute respiratory infection (SARI) between January 2006 to December 2016 per year per site. The sentinel sites were composed of different 17 hospitals and 34 health centers nationwide that were chosen based on their geographic locations and their capacity to qualify based on the criteria set by the DOH. Samples were placed in a viral transport medium (VTM) or universal transport medium (UTM) and stored at the institutional biobank (-80oC). According to the World Health Organization (WHO), ILI cases were defined as patients with acute respiratory illness with cough, runny nose, and/or sore throat with history of fever (38oC or above) with or without other system manifestations within the past five days. Meanwhile, SARI cases were defined by the Philippine Department of Health (DOH) as patients with an acute respiratory illness that fits the ILI case definition and requires hospitalization. Specifically, the integrated management of childhood illness (IMCI) guidelines also included in the SARI surveillance any child between two months to five years of age suspect case for pneumonia with cough or difficulty of breathing. For children with severe pneumonia, any child between two months and five years of age with danger signs including: inability to drink or breastfeed, vomits everything, convulsion, lethargic or unconscious, and with chest indrawing or stridor in calm child .