Figure 2.

Schematic representation of the Wallinga-Teunis algorithm extended with spatial information. Farm i could get infection from Farm j, but it also could get infection from Farms k₁, k₂, and k₃. In this example, the most likely time difference between onset of symptoms is 4 days (based on the serial interval distribution, given below the x-axis), and the most likely distance between farms is short (<1 km). Therefore, Farm j is the most likely farm to have infected Farm i (this scenario maximizes the probability in both dimensions). See the online Technical Appendix (wwwnc.cdc.gov/EID/article/19/6/12-1641-Techapp1.pdf) for details.