Seasonal patterns of respiratory syncytial virus, influenza A virus, human metapneumovirus, and parainfluenza virus type 3 infections on the basis of virus isolation data between 2004 and 2011 in Yamagata, Japan.

Most acute respiratory infections (ARIs) are thought to be associated with respiratory viruses that cause similar symptoms. Therefore, assessment of clinical and epidemiologic features of these viruses is important for diagnosing a viral infection. We collected 13,325 nasopharyngeal specimens from patients with ARIs and isolated the virus using a microplate method involving 7 cell lines between 2004 and 2011 in Yamagata, Japan. We isolated a total of 5,483 viruses. Respiratory syncytial virus (RSV), influenza A virus (FluA), human metapneumovirus (hMPV), and human parainfluenza virus type 3 (hPIV3) showed clear yearly seasonal patterns; generally, RSV infections peaked at the end of the year, FluA infections peaked between January and March, hMPV infections peaked between March and April, and hPIV3 showed seasonal outbreaks between May and July. Further, RSV, hMPV, and hPIV3 were commonly isolated in 12.0-13.1% of specimens from children aged less than 4 years, whereas FluA was isolated in 7.3-8.2% of specimens from school-aged children. A generalized view of seasonality and age distribution, particularly on the basis of longitudinal epidemiological data, will be helpful for medical decision-making, including decisions related to the use of rapid test kits, selection of antiviral treatments, restriction of antibiotic therapy, and implementation of infection control strategies.