The index case or primary case is the initial patient in the population of an epidemiological investigation.[1][2] The index case may indicate the source of the disease, the possible spread, and which reservoir holds the disease in between outbreaks. The index case is the first patient that indicates the existence of an outbreak. Earlier cases may be found and are labeled primary, secondary, tertiary, etc.[3] "Patient Zero" was used to refer to the index case in the spread of HIV in North America.[4]
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In the early years of the AIDS epidemic, there was controversy about a so-called Patient Zero, who was the basis of a complex transmission scenario compiled by Dr. William Darrow and colleagues at the U.S. Centers for Disease Control and Prevention (CDC).[5] This epidemiological study showed how Patient Zero had infected multiple partners with HIV, and they, in turn, transmitted it to others and rapidly spread the virus to locations all over the world(Auerbach et al., 1984). The CDC identified Gaëtan Dugas as the first person to bring HIV from Africa to the United States and to introduce it to gay bathhouses. [6]
Journalist Randy Shilts subsequently wrote about Patient Zero, based on Darrow's findings,[5] in his 1987 book And the Band Played On, which identified Patient Zero as Gaëtan Dugas.[7] Dugas was a flight attendant who was sexually promiscuous in several North American cities, according to Shilts' book. He was vilified for several years as a "mass spreader" of HIV, and seen as the original source of the HIV epidemic among homosexual men.[5] Four years later, Darrow repudiated the study methodology and how Shilts had represented its conclusions.[5]
A 2007 study published in the Proceedings of the National Academy of Sciences by Michael Worobey and Dr. Arthur Pitchenik claimed that, based on the results of genetic analysis, HIV probably moved from Africa to Haiti and then entered the United States around 1969,[8] probably through a single immigrant.
The term "Patient Zero" is now used in the media to refer to the index case for infectious disease outbreaks, as well as for computer virus outbreaks, and, more broadly, as the source of ideas or actions that have far-reaching consequences.[9][10][11][12][13]
Max Brooks's novel World War Z: An Oral History of the Zombie War begins with the account of the "Patient Zero" from which a zombie pandemic began.