Fig. 6.

Infectious disease transmission between five cities under a specific travel pattern (A/B→C→D/E)^*1 with different surveillance strategies (surveillance rate^⁎2 = 90%). The black solid lines represent the flow of tourists from their home cities to other cities and the black dashed lines represent the flow of tourists returning from other cities to their home cities. The red solid/dashed lines show the monitored route. (a) Source city A exit surveillance. (b) Second downstream city D entry surveillance. (c) Hub city C entry surveillance. (d) Hub city C exit surveillance. (e) Both hub city C entry and exit surveillance. (f) No surveillance.

^*1${\delta }_{AC}={\delta }_{BC}=1\%$; ${\delta }_{CD}={\delta }_{CE}=0.5\%$.

^⁎2 A 90% surveillance rate means that 90% of infected tourists are monitored when they move between cities. These people are isolated in hospitals and then leave from the hospital upon recovery.