How do scientist find "patient zero" during outbreaks?

Answer 1

Oftentimes it’s done by boots on the ground detective work. You have your patient that presents with a disease, and you find out who they’ve been in contact with. You go and speak with those people, and see who has had similar symptoms or disease. And you make a flow chart, tracing back to the first person that presented. And that’s patient zero. (Or O, for origin)