The Rules of Contagion: Why Things Spread - and Why They Stop

by Adam Kucharski

and jobs – of having large numbers of people with drug addiction. Because the success of different control strategies can vary between the three stages of a drug epidemic, it’s crucial to know what stage we’re currently in. In theory, it should be possible to work this out by estimating the annual numbers of new users, existing users, and heavy users. But the complexity of the opioid crisis – with its mix of prescription and illegal use, makes it very difficult to pick these things apart. There are some useful data sources – such as visits to emergency rooms and results of post-arrest drug tests – but this information has become harder to get hold of in recent years. We can’t draw a neat graph showing the different stages of drug use like we can for the Yambuku Ebola outbreak, because the data simply aren’t available. It’s a common problem in outbreak analysis: things that aren’t reported are by definition tough to analyse.