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The index case, primary case, or patient zero is the initial patient in the population of an epidemiological investigation, or more generally, the first case of a condition or syndrome (not necessarily contagious) to be described in the medical literature, whether or not the patient is thought to be the first person affected. An index case will sometimes achieve the status of a "classic" case in the literature, as did Phineas Gage.
Contents
- Gatan Dugas case Patient Zero
- Other index patients
- In journalism and documentaries
- In fiction
- References
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. The term primary case can only apply to infectious diseases that spread from human to human, and refers to the person who first brings a disease into a group of people.
"Patient Zero" was used to refer to the supposed index case in the spread of HIV in North America.
In genetics, the index case is the case of the original patient (propositus or proband) that stimulates investigation of other members of the family to discover a possible genetic factor.
Gaëtan Dugas case ("Patient Zero")
In the early years of the AIDS epidemic, a “patient zero” transmission scenario was compiled by Dr. William Darrow and colleagues at the U.S. Centers for Disease Control and Prevention (CDC). 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 a carrier of the virus from Europe to the United States and spreading it to other men he encountered at gay bathhouses.
Journalist Randy Shilts subsequently wrote about Patient Zero, based on Darrow's findings, in his 1987 book And the Band Played On, which identified Patient Zero as Gaëtan Dugas. 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. Four years later, Darrow repudiated the study's methodology and how Shilts had represented its conclusions.
A 2007 study published in the Proceedings of the National Academy of Sciences of the United States by Michael Worobey and Dr. Arthur Pitchenik claimed that, based on the results of genetic analysis, current North American strains of HIV probably moved from Africa to Haiti and then entered the United States around 1969, probably through a single immigrant. However, Robert Rayford died in St. Louis, Missouri, of complications from AIDS in 1969, and most likely became infected before 1966, so there were prior carriers of HIV strains in North America.
The phrase "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.
David Heymann, infectious-disease epidemiologist at the London School of Hygiene & Tropical Medicine, has questioned the importance of finding patient zero and has said: “Finding patient zero may be important in some instances, but only if they are still alive and spreading the disease. And more often than not, especially in large disease outbreaks, they’re not."
Other index patients
In journalism and documentaries
The thirteenth season of the WNYC radio series Radiolab included an hour-long segment on patients zero.