Physician Gary Slutkin spent a decade fighting tuberculosis, cholera and HIV/Aids epidemics in Africa.
When he returned to the United States, he thought he had escaped brutal epidemic deaths.
But then he began to look more carefully at gun violence, noting that its spread followed the patterns of infectious diseases.
Slutkin's theory is revolutionary because it is among the first to treat gun violence not as a moral or political problem, but as a medical issue to be solved using scientific methods.
Join Dr Slutkin in Chicago to meet the "violence interrupters" - many of whom are reformed criminals - working to end gun violence on their streets.
READ MORE: Is gun violence in the US infectious?
Source: Al Jazeera