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)?
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Patient Zero was a name given to the suspected index case of HIV, but index case is the general term. Since then however, somewhat understandably given the fame and infamy of HIV, “Patient Zero” has entered the public lexicon as a synonym for index case.
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.
It was never a zero. The label was actually patient “Oh” like the letter. It stood for outside. as in the case came from outside of the state that was doing the investigation.
>William Darrow, the CDC investigator who was eventually able to expand the Los Angeles cluster to connect forty cases in several cities, has repeatedly maintained that the study was always meant to investigate the transmissibility, and never the origin, of the newly recognized syndrome. He acknowledged in a 2008 interview that the term “patient O”—the letter “O” abbreviating the patient’s “Out[side]-of-California” residential status—evolved within the CDC to become the numerical “patient 0.” Nevertheless, Darrow downplayed the more capacious definitions associated with the word “zero”:
[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4046389/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4046389/)
It’s become a slang but isn’t used in epidemiology, which I do for a living.
The index case is first case noticed that started the investigation. It doesn’t have anything to do with who got it first. Pathogens don’t usually leave easy traces. So finding the true first person to catch a virus is practically impossible.
I use evolutionary analysis to compare virus genomes and given enough samples you can come up with a timeline of how the virus is evolving. You can place the pathogen roughly along that timeline but you would need extraordinary luck to find the true person where a particular mutation took place. Even then you wouldn’t be able to tell if the mutation happen in them or if it happened in a previous case. It can take some time for a mutation to come to prominence in a pathogen population.
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