Figure 3.

The searching time-buffer (T1) and time-threshold (T2) from the cases. The onset time of illness of cases a, b, and c are t, t′, and t′′, respectively. Both onset time of case b and c fall in the shifting zone of the case a (the range between t + T1 and t + T2), thus two shifting links (a,b) and (a–c) are identified. The shifting links (b–d), (c–d), (c–e), and (d–e) are found using the same concept. The onset time of case c falls inside the neighboring zone of case b (the range between t′ and $t\prime +T1$), therefore the relationship between (b,c) is identified as a neighboring pair. There is no direct relationship between (a–d), (a–e), and (b–e), because the latter falls beyond the shifting zone of the former.