Monthly distribution of respiratory viral infection in 924 patients with ILI. Each viral pathogen tested in our study was plotted for each month in 2010. The percent of admitted patients infected is shown on the y axis as a function of the month on the x axis. In China, the four seasons were generally recognized as spring (March–May), summer (June–August), fall (September–November), and winter (December–February). Respiratory viral agents usually have characteristic seasonal patterns. The peak of sFluA (H3N2) was from August–September, sFluB from March–May, and the peak of H1N1pdm09 occurred in January. RSV infection occurred predominantly from December–February and usually was observed in co-infection with sFluA, sFluB, HMPV, and ADV. PIV and ADV were detected throughout the year without significant seasonality in 2010.