Figure 1. Schematic representation of steps required to correctly identify secondary cases of infected individuals.

Each step is a binary variable and represents a point in the process where failure can occur. Steps 1–3 coincide with Phase 1 (identifying positive index cases). Steps 4 and 5 coincide with phase 2 (identifying contacts of positive cases). Finally, steps 6 and 7 coincide with Phase 3 (identifying positive cases among contacts).