To epidemiologists, does “index case” and “patient zero” both mean the same thing? That the patient is the very first person to contract the virus before it got to other people (used as a pinpoint)?

Question

To epidemiologists, does “index case” and “patient zero” both mean the same thing? That the patient is the very first person to contract the virus before it got to other people (used as a pinpoint)?

In: 39

Answer 1

Index case and patient zero mean the same thing: there are the first identified patient in a particular epidemic. It doesn’t mean that they are the first person to ever catch a particular disease; in most cases, the first person to ever become infected with a disease is unknown. HIV, for example, is thought to have emerged in the early 20th century as a result of a mutation of SIV, but no data currently exists on who its earliest infectees were.

For another example, the index case/patient zero of the 1976 outbreak of Ebola Zaire was Mabalo Lokela, a 44-year-old headmaster of a local school. Was he the first person to ever catch Ebolavirus? Probably not, but he’s the first identified person in that outbreak to have fallen ill, so he’s still the index case.