Index case

initial patient in the population of an epidemiological investigation

The index case (occasionally referred to as patient zero) is the first patient in a disease epidemic within a large population,[1] or the first documented patient included in an epidemiological study.[2]


  1. "Diseases – Activity 1 – Glossary, page 3 of 5". Retrieved 2017-11-10.
  2. "WordNet Search – 3.0". Princeton University, Retrieved 3 November 2010.