The hops were on communities connected by water supplies, not social graphs. In the graph of communities connected by water supplies, 4 hops is relatively short

The hops were on communities connected by water supplies, not social graphs. In the graph of communities connected by water supplies, 4 hops is relatively short. (See Figure 3b in http://arxiv.org/pdf/1208.2534v1.pdf http://arxiv.org/pdf/1208.2534v1.pdf) Unfortunately, I agree with you that it is difficult to judge the efficacy of "less than 4 hops" without providing some network metrics. By eye-balling figure 3b, it looks like the graph diameter is in the 30s, and the average degree of a community appears to be about three. Given an outbreak, less than 4 hops given (initially) limited surveillance could be important.