Children with influenza usually shed viruses from the several days before onset of clinical symptoms, and viruses are isolated for one or two weeks after onset. Point-of-care rapid diagnostic tests are useful to guide use of antiviral agents, appears over 90% sensitivity and specificity for influenza A with nasopharyngeal specimens compared with cell culture. The detection limits of these test kits are 103 pfu or over, so it is necessary to consider viral load in clinical specimens for diagnosis with these kits. Viral load are decreased after the start of antiviral agents, but influenza viruses are isolated in more than half of pediatric patients when fever get down, and resistant viruses are detected in some of these patients. It is very important for influenza control to investigate on viral shedding and resistant viruses.