Figure 3.

An illustration of the two-step tracing at the household level. We assume that all within-household contacts are always traced. For both one- and two-step tracing at the household level, all household members undergo quarantine and tracing regardless of whether they are the index case or not. In both of these examples, all of the individuals have been placed under quarantine or isolation once detected (for the index case) or traced. Households who were not successfully traced are not shown here. (Online version in colour.)