The index case or patient zero is the first documented patient in a disease epidemic within a population, or the first documented patient included in an epidemiological study. It can also refer to 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 can achieve the status of a "classic" case study in the literature, as did Phineas Gage, the first known person to exhibit a definitive personality change as a result of a brain injury.
The index case may or may not indicate the source of the disease, the possible spread, or which reservoir holds the disease in between outbreaks, but may bring awareness of an emerging outbreak. Earlier cases may or may not be found and are labeled primary or coprimary, 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. In epidemiology, the term is often used by both scientists and journalists alike to refer to the individual known or believed to have been the first infected or source of the resulting outbreak in a population as the index case, but such would technically refer to the primary case.
Origin of patient zero
"Patient zero" was used to refer to the supposed source of HIV outbreak in the United States, flight attendant Gaëtan Dugas in the popular press, but the term's use was based on a misunderstanding (and Dugas was not the index case). In the 1984 study of Centers for Disease Control and Prevention (CDC), one of the earliest recorded HIV-patients was code-named "patient O", which stands for "patient out of California". The letter O, however, was interpreted by some readers of the report as the numeral 0. The designation patient zero (for Gaëtan Dugas) was subsequently propagated by the San Francisco Chronicle journalist Randy Shilts in his book And the Band Played On in 1987. William Darrow, behavioral scientist of CDC responsible to figure out why gay men in Los Angeles were dying of a strange illness, said: "That's correct. I never labeled him Patient Zero".
The term has been expanded into general usage to refer to an individual identified as the first carrier of a communicable disease in a population (the primary case) or pandemics, or the first incident in the onset of a catastrophic trend. In some cases, a known or suspected patient zero may be informally referred to as an index case for the purpose of a scientific study, such as the two-year-old boy in a remote village in Guinea who was thought to be the source of the largest Ebola virus outbreak in history, or an unknown one, such as the mysterious patient zero of COVID-19.
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.
In the early years of the AIDS epidemic, a patient zero transmission scenario was compiled by William Darrow and colleagues at the United States 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 causing rapid spread of 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, who spread it to other men he had sexual contact with 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 being 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 was 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 by Michael Worobey and Arthur Pitchenik published in the Proceedings of the National Academy of Sciences of the United States of America claimed that, based on the results of genetic analysis, current North American strains of HIV probably moved from Africa to Haiti before entering the United States around 1969, probably through a single immigrant. However, a teenager named Robert Rayford died in St. Louis, Missouri, possibly of complications from AIDS in 1969, having most likely become infected with the virus before 1966. This would imply that there were prior carriers of HIV-strains in North America.
The phrase patient zero is now used in the media to refer to the primary 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, professor of Infectious Disease Epidemiology at the London School of Hygiene & Tropical Medicine, and formerly with the World Health Organization (WHO), has questioned the importance of finding patient zero, stating, "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."
- Mary Mallon ("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.
- The first recorded victim of Ebola was a 44-year-old schoolteacher named Mabalo Lokela, who died on 8 September 1976, 14 days after symptom onset.
- 64-year-old Liu Jianlun, a Guangdong doctor, transmitted SARS internationally by infecting other super-spreaders during a stay in the Hong Kong Metropole Hotel in 2003.
- A baby in the Lewis House at 40 Broad Street, named Frances Lewis, is considered the index patient in the 1854 cholera outbreak in the Soho neighborhood of London. (The Ghost Map, Steven Johnson, 2005.)
- Édgar Enrique Hernández may be patient zero of the 2009 flu pandemic. He recovered, and a bronze statue has been erected in his honor. Maria Adela Gutierrez, who contracted the virus about the same time as Hernández, became the first officially confirmed fatality.
- One-year-old Emile Ouamouno is believed to be patient zero in the 2014 Ebola epidemic in Guinea and West Africa.
- 51-year-old Jesus Lujan was the index case of the 1924 Los Angeles pneumonic plague outbreak which killed 33.
- Sgt. Albert M. Gitchell is commonly believed to be the index patient of the Spanish flu, which killed 50,000,000 from 1918 to 1920. Gitchell survived and died in 1968.
- As for the COVID-19 pandemic, there are many known "patient zeros" across the world known for different symptoms and stories. Out of Los Angeles, patient zero Gregg Garfield spent 64 days in the hospital, including 30 days of coma-state after contracting the virus on a ski trip. Doctors said he had a 1% chance to live. He survived, but had fingers and toes amputated.
- Another patient zero of the COVID-19 pandemic includes an elderly man who was diagnosed on 1 December 2019, someone who had no contact with the Huanan Seafood Wholesale Market. Three other people experienced symptoms in the following days who also did not have contact with the Market.
- Proband – person who undergoes an examination or is the subject of a medical genetics study
- Misconceptions about HIV/AIDS – Misinformation about the HIV/AIDS and its spread
- "Diseases – Activity 1 – Glossary, page 3 of 5". science.education.nih.gov. Archived from the original on 2017-11-10. Retrieved 2017-11-10.
- "WordNet Search – 3.0". Princeton University, wordnetweb.princeton.edu. Archived from the original on 3 March 2012. Retrieved 3 November 2010.
- "Why Brain Scientists Are Still Obsessed With The Curious Case Of Phineas Gage". NPR.org. Archived from the original on 2019-08-28. Retrieved 2017-11-18.
- "Sporadic STEC O157 Infection: Secondary Household Transmission in Wales". CDC.gov. Centers for Disease Control and Prevention, USA. 1 January 1994. Archived from the original on 28 May 2010. Retrieved 3 November 2010.
- Giesecke, Johan (2014). "Primary and index cases". The Lancet. 384 (9959): 2024. doi:10.1016/s0140-6736(14)62331-x. PMID 25483164. S2CID 12454399.
- "index case". CollinsDictionary.com. HarperCollins. Retrieved 2017-11-18.
- Davis, Nicola (27 October 2016). "Gaétan Dugas: 'patient zero' not source of HIV/Aids outbreak, study confirms". The Guardian. Archived from the original on 27 October 2016. Retrieved 26 October 2016.
- DOUCLEFF, MICHAELEEN (October 26, 2016). "Researchers Clear 'Patient Zero' From AIDS Origin Story". NPR. Archived from the original on 30 April 2021. Retrieved 1 May 2021.
- "Patient Zero – definition of Patient Zero in the Medical dictionary – by the Free Online Medical Dictionary, Thesaurus and Encyclopedia". medical-dictionary.thefreedictionary.com. Archived from the original on 24 February 2021. Retrieved 3 November 2010.
- "patient zero | Definition of patient zero in English by Oxford Dictionaries". Oxford Dictionaries | English. Archived from the original on 2017-12-01. Retrieved 2017-11-18.
- "Ebola outbreak: 'Patient zero' at start of deadly virus spread". The Independent. 2014-08-11. Archived from the original on 2017-12-01. Retrieved 2017-11-18.
- Page J, Hinshaw D, McKay B (26 February 2021). "In Hunt for Covid-19 Origin, Patient Zero Points to Second Wuhan Market – The man with the first confirmed infection of the new coronavirus told the WHO team that his parents had shopped there". The Wall Street Journal. Retrieved 27 February 2021.
- Duarte F (24 February 2020). "As the cases of coronavirus increase in China and around the world, the hunt is on to identify "patient zero"". BBC News. Retrieved 22 March 2020.
- "Definition of index case". The free medical dictionary by farlex. Archived from the original on 2013-05-12. Retrieved 2013-05-11.
- "Search for patient zero: uncovering malware infection at the source". Infosecurity Magazine. 10 July 2012. Archived from the original on 31 March 2017. 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.
- Auerbach, David M.; Darrow, William W.; Jaffe, Harold W.; Curran, James W. (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.
- "The Origin of HIV and the First Cases of AIDS". avert.org. AVERT. Archived from the original on 2010-11-04. Retrieved 2010-11-03.
- 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.
- Matt & Andrej Koymasky - Famous GLTB - Gaëtan Dugas Archived December 14, 2005, at the Wayback Machine
- Bowdler, Neil (2007-10-30). "Key HIV strain 'came from Haiti'". BBC News. Archived from the original on 2012-05-21. Retrieved 2010-05-05.
- "HIV Spread from Haiti to NYC in 1970". The Scientist. Archived from the original on 2021-07-10. Retrieved 2021-07-10.
- 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
- "Have Doctors Found Swine "Patient Zero?"". CBS News. 2009-04-29. Archived from the original on 2009-04-29. Retrieved 2009-04-29.
- "Researchers trawl for Conficker's 'Patient Zero' – Techworld.com". news.techworld.com. Archived from the original on 2011-07-18. Retrieved 2010-11-03.
- "Patient Zero". TV.com. 2006-03-20. Archived from the original on 2011-12-27. Retrieved 2010-11-03.
- Lemos, Robert. "Witty worm traced to 'Patient Zero'". The Register. Archived from the original on 2017-08-10. Retrieved 2017-08-10.
- "That Man in the White House". The Weekly Standard. 28 November 2003. Archived from the original on 4 June 2011. Retrieved 3 November 2010.
- "WHO | Members of, and Advisers to, the International Health Regulations (2005) Emergency Committee on Zika virus and observed increase in neurological disorders and neonatal malformations". WHO. Archived from the original on 2019-04-21. Retrieved 2019-12-25.
- Mohammadi, Dara (2015-01-15). "Finding patient zero". The Pharmaceutical Journal. 294 (7845). Archived from the original on 2015-01-24. Retrieved 2015-01-16.
- "NOVA | The Most Dangerous Woman in America | In Her Own Words". PBS. 1938-11-11. Archived from the original on 2010-04-26. Retrieved 2010-11-03.
- "Ebola haemorrhagic fever in Zaire, 1976" (PDF). Bull. World Health Organ. 56 (2): 271–93. 1978. PMC 2395567. PMID 307456. Archived from the original (PDF) on 8 August 2014. Retrieved 22 May 2018.
- "How SARS changed the world in less than six months" (PDF). Bulletin of the World Health Organization. 81 (8). 2003. Archived (PDF) from the original on 2012-04-05. Retrieved 2011-10-18.
- Laurance, Jeremy (2003-04-24). "One family went on holiday – and made Toronto a global pariah". The Independent. London. Archived from the original on 2018-05-22. Retrieved 2010-05-05.
- "Molecular Interventions – CLOCKSS" (PDF). Retrieved 14 October 2014.
- "Have Doctors Found Swine "Patient Zero?"". CBS News. 2009-04-29. Archived from the original on 2011-08-05. Retrieved 2010-11-03.
- "Statue erected of first boy in world who caught swine flu". mirror.co.uk. Mirror. Archived from the original on 2014-05-22. Retrieved 2009-04-25.
- Beukes, Suzanne (2014-10-28). "Finding Ebola's 'patient zero'". The Guardian. Archived from the original on 2014-12-19. Retrieved 28 November 2014.
- ""I'm back in action," One of the first Americans who contracted COVID-19 speaks about his recovery". 13 March 2021.
- Duarte, Fernando. "Who is 'patient zero' in the coronavirus outbreak?". www.bbc.com.
- Savitz, Eric (5 June 2012). "Finding Patient Zero: The Key To Responding To Malware Attacks". Forbes. Archived from the original on 31 March 2017. 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.
- Merica, Dan (October 21, 2014). "Lewinsky makes emotional plea to end cyberbullying". CNN. Archived from the original on October 22, 2014. Retrieved October 22, 2014.
- "Mapping the Spread of Viruses / Contagions via Contact Tracing". orgnet.com. Orgnet. Retrieved 2010-11-03.
- Letter to the New York Review of Books (vol. 35, number 19, December 8, 1988) by Dr. Andrew Moss, Dept. of Epidemiology and International Health, San Francisco, regarding the “patient zero” myth.
- "Patient Zero - Updated". Radiolab. Season 13, Episode 3.