Understanding the characteristics and patterns of numbers of ED visits over time from our established ED-SSS in Taiwan is very crucial before we set up appropriate threshold levels of different syndrome groups for outbreak detection, There was a significant difference in daily counts between weekdays and weekends, which occurred on a weekly basis. ED visits were 1.288-fold-higher on weekends than on weekdays (p < 0.001), while national During this first year study, the ED-SSS found patients throughout Taiwan were more likely to seek emergency medical services at medical centers than at district or local hospitals. Most patients visiting ED were 60 years old or older (21.46%) or below the age of 10 years old (18.55%). These two groups were also at greatest risk for various infectious diseases, especially influenza (Table 3) . Young adults between 20 to 39 years old ranked the third most frequent visitors to ED (17.43%), though traffic accidents, not infectious diseases, were the main reasons for their visits. These age distributions suggest that the newly established ED-SSS was capable of providing information for the age groups most at risk for severe cases of infectious diseases in Taiwan. Male ED patients slightly outnumbered female ED patients (male : female = 1.12:1), which approximates the general distribution of gender in Taiwan (male/female ratio = 1.10). For elderly ED patients (age > 65 years old), the male/female ratio in our sample was the same as general population (male: female = 1.10:1).