During the study period, 5,975 children (aged 2 months-15 years) with influenza-like illness were seen at our hospital. Among them, the 2,971 patients were positive by RT-PCR, and 217 patients were admitted to the isolation wards. The hospitalization rate was 7.3%. The mean age of the patients (2,971 cases) was 7.6 ± 4.1 years of age and the male-to-female ratio was 1.1:1 (1,581/1,390). The age distribution of the patients is shown in Figure 1 . Children of all age groups except infants had a relatively even rate of infection ( Figure 1 , gray bars). The numbers of new patients each week is shown in Figure 2 . There was an explosive pattern, with over three quarters of the cases occurring during a single month (the 43rd-47th weeks of 2009; 18 October to 14 November). The age distribution and the weekly case rate of the patients admitted to hospital (217 cases) are also shown on Figure 1 and 2 (black bars). These demonstrated similar patterns to those of the total patient cohort. For hospitalization rates, younger children (0-4 years, 9.8%, 75/762) showed higher admission rates than older children (5-9 years, 8.6%, 104/1216 and 10-15 years, 3.8%, 38/993). 