Index case

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The index case, primary case, or patient zero is the initial patient in the population of an epidemiological investigation,[1][2] 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.[citation needed] An index case will sometimes achieve the status of a "classic" case in the literature, as did Phineas Gage.

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] 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.[4]

"Patient Zero" was used to refer to the supposed[5] index case in the spread of HIV in North America.[6]

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.[7]

The term can also be used in non-medical fields to describe the first individual affected by something negative that since propagated to others, such as the first user on a network infected by malware.[8]

Gaëtan Dugas case ("Patient Zero")[edit]

A now disproven 1984 paper[9] linked 40 AIDS patients by sexual contact. Of those patients, Dugas was supposedly the first to experience an onset of symptoms of AIDS. In the above graph, Dugas is represented by the circle highlighted in red.

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).[10] 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.[11]

Journalist Randy Shilts subsequently wrote about Patient Zero, based on Darrow's findings,[10] in his 1987 book And the Band Played On, which identified Patient Zero as Gaëtan Dugas.[12] 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.[10]

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,[13] 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.[14][15]

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.[16][17][18][19][20]

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."[21]

Other index patients[edit]

  • Mary Mallon (a.k.a. “Typhoid Mary”) was an index case of a typhoid outbreak in the early 1900s. An apparently healthy carrier, she infected 47 people while working as a cook. She eventually was isolated to prevent her from spreading the disease to others.[22]
  • The first recorded victim of the Ebola virus was a 44-year-old schoolteacher named Mabalo Lokela, who died on 8 September 1976, 14 days after symptom onset[citation needed]
  • 64-year-old Liu Jianlun, a Guangdong doctor, transmitted SARS during a stay in the Hong Kong Metropole Hotel in 2003.[23][24]
  • A baby in the Lewis House at 40 Broad Street is considered the index patient in the 1854 cholera outbreak in the Soho neighborhood of London. (The Ghost Map, Steven Johnson, 2005.)[25]
  • Édgar Enrique Hernández may be patient zero of the 2009 swine flu outbreak.[26] He recovered, and a bronze statue has been erected in his honor.[27] Maria Adela Gutierrez, who contracted the virus about the same time as Hernández, became the first officially confirmed fatality.
  • Two-year-old Emile Ouamouno is believed to be the index patient in the 2014 Ebola epidemic in Guinea and West Africa.[28]

Non-medical usage[edit]

The term is used to identify the first computer or user to be infected with malware on a network, which then infected other systems.[8][29] Monica Lewinsky has described herself as the "patient zero" of online harassment, meaning that she was the first person to receive widespread public harassment via the internet.[30]

In the media[edit]

In journalism and documentaries[edit]

The thirteenth season of the WNYC radio series Radiolab included an hour-long segment on patients zero.[31]

In fiction[edit]

  • The film Outbreak focuses around the search for a patient zero of an epidemic.
  • The novel Rant stars the character Rant Casey, patient zero of the book's rabies epidemic.
  • The phone game Plague Inc. can have the CDC look for Patient Zero for more info on the player's virus.
  • In the video game Dead Rising 3 the protagonist, Nick Ramos, is patient zero of the zombification phenomenon.
  • The film Contagion character Elizabeth Emhoff is patient zero of the fatal MEV-1 virus.
  • In the Planet of the Apes film series, Robert Franklin (portrayed by Tyler Labine) is Patient Zero of the Simian Flu Pandemic.
  • In the game Prototype, Alex Mercer steals something in GenTek labs and becomes the unwilling patient zero for the virus the lab created.
  • In the TV series Fear The Walking Dead, Gloria is speculated to be patient zero in the show's pilot.
  • In the animated TV series South Park, in S1E7 episode Pinkeye Kenny became patient zero of zombie epidemic.
  • In the book series The Passage, Timothy Fanning is patient zero of the virus that caused the near extinction of humanity and responsible for the outbreak of the new "viral" race of vampires.
  • In the 2013 film World War Z the protagonist Gerry Lane (Brad Pitt) search for Patient Zero of a Zombie Apocalypse.
  • In the tokusatsu series Kamen Rider Ex-Aid, the protagonist Emu Hojo is Patient Zero of a digital virus that kills those infected by it and replace them with videogame characters. Although he manages to survive and develop immunity, the infection spreads, threatening humanity.

See also[edit]


  1. ^ "Diseases - Activity 1 - Glossary, page 3 of 5". Retrieved 2010-11-03. 
  2. ^ "WordNet Search - 3.0". Princeton University, Retrieved 3 November 2010. 
  3. ^ "Sporadic STEC O157 Infection: Secondary Household Transmission in Wales". Centers for Disease Control and Prevention, USA, 1 January 1994. Retrieved 3 November 2010. 
  4. ^ Giesecke, Johan. "Primary and index cases". The Lancet. 384 (9959). doi:10.1016/s0140-6736(14)62331-x. 
  5. ^
  6. ^ "Patient Zero - definition of Patient Zero in the Medical dictionary - by the Free Online Medical Dictionary, Thesaurus and Encyclopedia". Retrieved 3 November 2010. 
  7. ^ "Definition of index case". The free medical dictionary by farlex. 
  8. ^ a b "Search for patient zero: uncovering malware infection at the source". Infosecurity Magazine. 10 July 2012. Retrieved 31 March 2017. Medical researchers look for patient zero to find out where a virus outbreak started and what places and people patient zero came into contact with in order to contain the outbreak and prevent further infections. Similarly, infosec researchers need to look for the user who first introduced the malware into the network, which application was carrying the malware, and the files that are causing it to spread in order to contain it, eliminate it, and prevent reinfection, explained Huger, vice president of development at Sourcefire’s cloud technology group. 
  9. ^ Auerbach, D.M.; W.W. Darrow; H.W. Jaffe; J.W. Curran (1984). "Cluster of cases of the acquired immune deficiency syndrome. Patients linked by sexual contact". The American Journal of Medicine. 76 (3): 487–92. doi:10.1016/0002-9343(84)90668-5. PMID 6608269. 
  10. ^ a b c "The Origin of HIV and the First Cases of AIDS". AVERT, Retrieved 2010-11-03. 
  11. ^ Pence, G. E. (2008). Preventing the Global Spread of AIDS. In Medical Ethics Accounts of the Cases That Shaped and Define Medical Ethics (p. 331). New York, USA, McGraw-Hill.
  12. ^ Matt & Andrej Koymasky - Famous GLTB - Gaëtan Dugas Archived December 14, 2005, at the Wayback Machine.
  13. ^ Bowdler, Neil (2007-10-30). "Key HIV strain 'came from Haiti'". BBC News. Retrieved 2010-05-05. 
  14. ^ Patient-Zero Not to Blame The Scientist
  15. ^ Worobey, Michael et al "1970s and ‘Patient 0’ HIV-1 genomes illuminate early HIV/AIDS history in North America" Nature (2016) doi:10.1038/nature19827
  16. ^ "Have Doctors Found Swine "Patient Zero?"". CBS News. 2009-04-29. 
  17. ^ "Researchers trawl for Conficker's 'Patient Zero' -". Retrieved 2010-11-03. 
  18. ^ "Patient Zero". 2006-03-20. Retrieved 2010-11-03. 
  19. ^ Lemos, Robert. "Witty worm traced to 'Patient Zero'". The Register. 
  20. ^ "That Man in the White House". The Weekly Standard. 28 November 2003. Retrieved 3 November 2010. 
  21. ^ Mohammadi, Dara (2015-01-15). "Finding patient zero". The Pharmaceutical Journal. 294 (7845). Retrieved 2015-01-16. 
  22. ^ "NOVA | The Most Dangerous Woman in America | In Her Own Words". PBS. 1938-11-11. Retrieved 2010-11-03. 
  23. ^ "How SARS changed the world in less than six months" (PDF). Bulletin of the World Health Organization. 81 (8). 2003. 
  24. ^ Laurance, Jeremy (2003-04-24). "One family went on holiday – and made Toronto a global pariah". The Independent. London. Retrieved 2010-05-05. 
  25. ^ "Molecular Interventions - CLOCKSS" (PDF). Retrieved 14 October 2014. 
  26. ^ "Have Doctors Found Swine "Patient Zero?"". CBS News. 2009-04-29. Retrieved 2010-11-03. 
  27. ^ "Statue erected of first boy in world who caught swine flu". Mirror, Retrieved 2009-04-25. 
  28. ^ "Finding Ebola's 'patient zero'". The Guardian. Retrieved 28 November 2014. 
  29. ^ Savitz, Eric (5 June 2012). "Finding Patient Zero: The Key To Responding To Malware Attacks". Forbes. Retrieved 31 March 2017. In the physical world, the first thing researchers look for during an outbreak is patient zero. Where did the virus start and where are all of the places and who are all of the people it could have touched? In the cyber world this almost never happens. But it is just as fundamental. 
  30. ^ Merica, Dan (October 21, 2014). "Lewinsky makes emotional plea to end cyberbullying". CNN. Retrieved October 22, 2014. 
  31. ^ "Patient Zero - Updated". Radiolab. Season 13, Episode 3. Retrieved November 15, 2015.

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