Sample collection and pathogen detection
Respiratory samples, including nasopharyngeal swabs and aspirates, throat swabs and/or tracheal aspirates were collected from children admitted to Queen Mary Hospital, Hong Kong for any purpose. The study was approved by the joint Institutional Review Board of the University of Hong Kong and the Hospital Authority Hong Kong West Cluster Research Ethics Committee. The need for written consent was waived because testing for respiratory pathogens is standard and routine for all children admitted for an acute respiratory infection. Specimens were tested by multiplex RT-PCR for influenza A, influenza B, RSV, adenovirus, HPIV 1–4, HMPV, and enterovirus/rhinovirus as described previously (23).