The role of respiratory viruses in pediatric patients with severe lower respiratory tract infection (LRTI) is unclear in Japan. The purpose of this study was to investigate the prevalence of respiratory viruses in children with LRTI managed at the pediatric intensive care unit (PICU) in a single center in Chiba, Japan. We examined 153 patients with LRTI who needed ventilatory support including high-flow nasal cannula oxygen therapy between April 2012 and March 2017; 116 by immunochromatography and 37 by PCR. Nasal swab samples were then examined using immunochromatography assay kits for respiratory syncytial virus (RSV), human metapneumovirus (hMPV), and influenza virus (flu). For PCR, viral antigen nucleic acids were obtained from nasal swabs. Each sample was examined by (RT-) PCR for RSV, enterovirus (EV), hMPV, human bocavirus (HBoV), parainfluenza virus (PIV), and adenovirus (AdV). Clinical characteristics, disease course, and prognosis were investigated. Of 153 patients with a median age of 13 months (0 months-13 years), 73 were male, and 59% had previously had an underlying disease and/or disability. We detected at least 1 virus in 147 patients (96%); 10 patients (6.5%) had co-infection with different viruses. RSV (53%) was the most common, followed by hMPV (20%), EV (5.2%), flu (4.6%), HBoV (4.6%), and PIV (2.6%). Infants were frequently positive for RSV or EV, whereas children over 1 year old were frequently positive for hMPV or HBoV. Seasonal variation was seen in each virus. Over half of the patients positive for RSV or flu were previously heathy children, but many patients positive for other viruses had some other disease or disability. Duration of PICU stay depended on patients' backgrounds rather than the causative virus. After LRTI, 1 patient dead, 2 patients received tracheotomy, and 1 started home oxygen therapy. In conclusion, RSV was the most common in LRTI pediatric patients in the PICU. Except for RSV and flu, patients frequently had some other disease/disability. Duration of PICU stay and prognosis often depends on the patient's background.
