A new idea is catching across the United States: crime and violence spread like viruses do, and a person’s overall health is deeply intertwined with a person’s safety. Living in a violent neighborhood can wreak havoc on physical and mental well-being, and poor health can, in turn, lead to dangerous behavior.

If dangerous behavior is like a contagious disease, perhaps positive relationships can serve as an antidote. Like inoculations against illnesses, some cities are finding that treating a few key carriers of harmful behavior or altering a few environments where the “illness” of disorder thrives, can increase the health and safety of an entire community.