Virus detection
All patients underwent a nasopharyngeal washing (NPW), obtained using 3 ml of sterile saline solution injected into each nostril and collected with a syringe. On NPW, a panel of reverse transcriptase-polymerase chain reaction (RT-PCR) or nested PCR methods was used for the detection of 14 respiratory viruses, including RSV, human rhinovirus (hRV), influenza (Flu) A and B, parainfluenza viruses (PIV) 1-3, adenovirus (ADV), human coronaviruses (hCoVs OC43, 229E, NL-63, HUKI), human metapneumovirus (hMPV) and human Bocavirus (hBoV), as described [9]. All specimens were collected within 24 hours of hospital admission.