Index case

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.{{cite web |url=https://www.cdc.gov/ncidod/EID/vol4no4/parry.htm |title=Sporadic STEC O157 Infection: Secondary Household Transmission in Wales |publisher=Centers for Disease Control and Prevention, USA |website=CDC.gov |date=1 January 1994 |access-date=3 November 2010 |archive-date=28 May 2010 |archive-url=https://web.archive.org/web/20100528175452/https://www.cdc.gov/ncidod/eid/vol4no4/parry.htm |url-status=live }} 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.{{cite journal|last=Giesecke|first=Johan|title=Primary and index cases|journal=The Lancet|volume=384|issue=9959|pages=2024|doi=10.1016/s0140-6736(14)62331-x|pmid=25483164|year=2014|s2cid=12454399}} 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.{{cite CD.com|index case|language=en-US|access-date=2017-11-18}}

"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).{{cite news|url=https://www.theguardian.com/science/2016/oct/26/patient-zero-gaetan-dugas-not-source-of-hivaids-outbreak-study-proves|title=Gaétan Dugas: 'patient zero' not source of HIV/Aids outbreak, study confirms|first=Nicola|last=Davis|date=27 October 2016|newspaper=The Guardian|access-date=26 October 2016|archive-date=27 October 2016|archive-url=https://web.archive.org/web/20161027000213/https://www.theguardian.com/science/2016/oct/26/patient-zero-gaetan-dugas-not-source-of-hivaids-outbreak-study-proves|url-status=live}} 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, a CDC behavioral scientist responsible for figuring out why gay men in Los Angeles were dying of a strange illness, said: "That's correct. I never labeled him Patient Zero".{{cite news |last1=DOUCLEFF |first1=MICHAELEEN |title=Researchers Clear 'Patient Zero' From AIDS Origin Story |url=https://www.npr.org/sections/health-shots/2016/10/26/498876985/mystery-solved-how-hiv-came-to-the-u-s |access-date=1 May 2021 |agency=NPR |date=October 26, 2016 |archive-date=30 April 2021 |archive-url=https://web.archive.org/web/20210430122054/https://www.npr.org/sections/health-shots/2016/10/26/498876985/mystery-solved-how-hiv-came-to-the-u-s |url-status=live }}

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.{{cite web |url=https://medical-dictionary.thefreedictionary.com/Patient+Zero |title=Patient Zero – definition of Patient Zero in the Medical dictionary – by the Free Online Medical Dictionary, Thesaurus and Encyclopedia |publisher=medical-dictionary.thefreedictionary.com |access-date=3 November 2010 |archive-date=24 February 2021 |archive-url=https://web.archive.org/web/20210224083623/https://medical-dictionary.thefreedictionary.com/Patient+Zero |url-status=live }}{{cite web|url=https://en.oxforddictionaries.com/definition/patient_zero|title=patient zero {{!}} Definition of patient zero in English by Oxford Dictionaries|website=Oxford Dictionaries {{!}} English|access-date=2017-11-18|archive-date=2017-12-01|archive-url=https://web.archive.org/web/20171201044041/https://en.oxforddictionaries.com/definition/patient_zero|url-status=dead}} 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,{{cite news|url=https://www.independent.co.uk/news/world/africa/ebola-outbreak-patient-zero-at-start-of-deadly-virus-spread-identified-by-scientists-as-a-two-year-9660864.html|title=Ebola outbreak: 'Patient zero' at start of deadly virus spread|date=2014-08-11|work=The Independent|access-date=2017-11-18|language=en-GB|archive-date=2017-12-01|archive-url=https://web.archive.org/web/20171201041743/https://www.independent.co.uk/news/world/africa/ebola-outbreak-patient-zero-at-start-of-deadly-virus-spread-identified-by-scientists-as-a-two-year-9660864.html|url-status=live}} or an unknown one, such as the mysterious patient zero of COVID-19.{{cite news | vauthors = Page J, Hinshaw D, McKay B |title=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 |url=https://www.wsj.com/articles/in-hunt-for-covid-19-origin-patient-zero-points-to-second-wuhan-market-11614335404 |date=26 February 2021 |work=The Wall Street Journal |access-date=27 February 2021 }}{{cite news| vauthors = Duarte F | date=24 February 2020|title=As the cases of coronavirus increase in China and around the world, the hunt is on to identify "patient zero".|work=BBC News|url=https://www.bbc.com/future/article/20200221-coronavirus-the-harmful-hunt-for-covid-19s-patient-zero|access-date=22 March 2020}}

In genetics, the index case is the case of the original patient (i.e. propositus or proband) that stimulates investigation of other members of the family to discover a possible genetic factor.{{cite web|title=Definition of index case|url=https://medical-dictionary.thefreedictionary.com/index+case|publisher=The free medical dictionary by farlex|access-date=2013-05-11|archive-date=2013-05-12|archive-url=https://web.archive.org/web/20130512051624/https://medical-dictionary.thefreedictionary.com/index+case|url-status=live}}

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.

{{main|Gaëtan Dugas}}

File:AIDS index case graph.svg |volume=76 |issue=3 |pages=487–92 |year=1984 |doi=10.1016/0002-9343(84)90668-5 |pmid=6608269 }} 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 labeled 0, highlighted in red.]]

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.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.

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.[https://andrejkoymasky.com/liv/fam/biod3/duga1.html Matt & Andrej Koymasky - Famous GLTB - Gaëtan Dugas] {{webarchive |url=https://web.archive.org/web/20051214123317/https://andrejkoymasky.com/liv/fam/biod3/duga1.html |date=December 14, 2005 }} 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.{{cite web| url=https://www.avert.org/origin-aids-hiv.htm| title=The Origin of HIV and the First Cases of AIDS| publisher=AVERT| website=avert.org| access-date=2010-11-03| archive-date=2010-11-04| archive-url=https://web.archive.org/web/20101104215824/https://www.avert.org/origin-aids-hiv.htm| url-status=live}}

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,{{cite news| url=https://news.bbc.co.uk/2/hi/health/7068574.stm| work=BBC News| title=Key HIV strain 'came from Haiti'| date=2007-10-30| access-date=2010-05-05| first=Neil| last=Bowdler| archive-date=2012-05-21| archive-url=https://web.archive.org/web/20120521084500/https://news.bbc.co.uk/2/hi/health/7068574.stm| url-status=live}} 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.{{cite web |url=https://www.the-scientist.com/?articles.view/articleNo/47352/title/HIV-Spread-from-Haiti-to-NYC-in-1970---Patient-Zero--Not-to-Blame/ |title=HIV Spread from Haiti to NYC in 1970 |website=The Scientist |access-date=2021-07-10 |archive-date=2021-07-10 |archive-url=https://web.archive.org/web/20210710141320/https://www.the-scientist.com/daily-news/hiv-spread-from-haiti-to-nyc-in-1970-patient-zero-not-to-blame-32644 |url-status=live }}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

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.{{cite news| url=https://www.cbsnews.com/news/have-doctors-found-swine-patient-zero/| work=CBS News| title=Have Doctors Found Swine "Patient Zero?"| date=2009-04-29| access-date=2009-04-29| archive-date=2009-04-29| archive-url=https://web.archive.org/web/20090429213725/https://www.cbsnews.com/stories/2009/04/29/earlyshow/main4976805.shtml| url-status=live}}{{cite web| url=https://news.techworld.com/security/113086/researchers-trawl-for-confickers-patient-zero/| title=Researchers trawl for Conficker's 'Patient Zero' – Techworld.com| publisher=news.techworld.com| access-date=2010-11-03| archive-url=https://web.archive.org/web/20110718062248/https://news.techworld.com/security/113086/researchers-trawl-for-confickers-patient-zero/| archive-date=2011-07-18| url-status=dead}}{{cite web|url=https://www.tv.com/shows/law-order/patient-zero-276048/|title=Patient Zero|publisher=TV.com|date=2006-03-20|access-date=2010-11-03|archive-date=2011-12-27|archive-url=https://web.archive.org/web/20111227051609/https://www.tv.com/shows/law-order/patient-zero-276048|url-status=live}}{{cite web| last=Lemos| first=Robert| title=Witty worm traced to 'Patient Zero'| url=https://www.theregister.co.uk/2005/05/25/witty_worm_traced/| publisher=The Register| access-date=2017-08-10| archive-date=2017-08-10| archive-url=https://web.archive.org/web/20170810135739/https://www.theregister.co.uk/2005/05/25/witty_worm_traced/| url-status=live}}{{cite web|url=https://www.weeklystandard.com/Content/Public/Articles/000/000/003/437txvzt.asp?pg=2|title=That Man in the White House|publisher=The Weekly Standard|date=28 November 2003|access-date=3 November 2010|archive-date=4 June 2011|archive-url=https://web.archive.org/web/20110604094453/https://www.weeklystandard.com/Content/Public/Articles/000/000/003/437txvzt.asp?pg=2|url-status=dead}}

David Heymann, professor of Infectious Disease Epidemiology at the London School of Hygiene & Tropical Medicine, and formerly with the World Health Organization (WHO),{{cite web|url=https://www.who.int/ihr/procedures/zika-ec-biographies/en/|title=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|website=WHO|access-date=2019-12-25|archive-date=2019-04-21|archive-url=https://web.archive.org/web/20190421202915/https://www.who.int/ihr/procedures/zika-ec-biographies/en/|url-status=live}} 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."{{cite journal| last1=Mohammadi| first1=Dara| title=Finding patient zero| journal=The Pharmaceutical Journal| date=2015-01-15| volume=294| issue=7845| url=https://www.pharmaceutical-journal.com/news-and-analysis/features/finding-patient-zero/20067543.article| access-date=2015-01-16| archive-date=2015-01-24| archive-url=https://web.archive.org/web/20150124084210/https://www.pharmaceutical-journal.com/news-and-analysis/features/finding-patient-zero/20067543.article| url-status=live}}

• Mary Mallon ("Typhoid Mary") was an index case of a typhoid outbreak in the early 1900s. An apparently healthy carrier, she infected at least 47 people while working as a cook. She eventually was isolated to prevent her from spreading the disease to others.{{cite web |url=https://www.pbs.org/wgbh/nova/typhoid/letter.html |title=NOVA | The Most Dangerous Woman in America | In Her Own Words |publisher=PBS |date=1938-11-11 |access-date=2010-11-03 |archive-date=2010-04-26 |archive-url=https://web.archive.org/web/20100426042928/https://www.pbs.org/wgbh/nova/typhoid/letter.html |url-status=live }}
• 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.{{cite journal | title = Ebola haemorrhagic fever in Zaire, 1976 | journal = Bull. World Health Organ. | volume = 56 | issue = 2 | pages = 271–93 | year = 1978 | pmid = 307456 | pmc = 2395567 | url = https://whqlibdoc.who.int/bulletin/1978/Vol56-No2/bulletin_1978_56(2)_271-293.pdf | url-status = dead | archive-url = https://web.archive.org/web/20140808213715/https://whqlibdoc.who.int/bulletin/1978/Vol56-No2/bulletin_1978_56%282%29_271-293.pdf | archive-date = 8 August 2014 | df = dmy-all | access-date = 22 May 2018 | author1 = Report of an International Commission }}
• 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.{{cite journal | url=https://www.scielosp.org/pdf/bwho/v81n8/v81n8a14.pdf | title=How SARS changed the world in less than six months | journal=Bulletin of the World Health Organization | year=2003 | volume=81 | issue=8 | access-date=2011-10-18 | archive-date=2012-04-05 | archive-url=https://web.archive.org/web/20120405125444/https://www.scielosp.org/pdf/bwho/v81n8/v81n8a14.pdf | url-status=live }}{{cite news | url=https://www.independent.co.uk/news/science/one-family-went-on-holiday-and-made-toronto-a-global-pariah-116428.html | work=The Independent | location=London | title=One family went on holiday – and made Toronto a global pariah | date=2003-04-24 | access-date=2010-05-05 | first=Jeremy | last=Laurance | archive-date=2018-05-22 | archive-url=https://web.archive.org/web/20180522183931/https://www.independent.co.uk/news/science/one-family-went-on-holiday-and-made-toronto-a-global-pariah-116428.html | url-status=live }}
• A baby in the Lewis House at 40 Broad Street, named Frances Lewis, is considered the index patient in the 1854 cholera outbreak in London, England.{{cite web|url=https://www.ph.ucla.edu/epi/snow/indexcase.html|title=Index case at 40 Broad Street|publisher=UCLA Fielding School of Public Health, Department of Epidemiology|access-date=10 February 2025}}
• Édgar Enrique Hernández may be patient zero of the 2009 flu pandemic.{{cite web |url=https://www.cbsnews.com/news/have-doctors-found-swine-patient-zero/ |title=Have Doctors Found Swine "Patient Zero?" |publisher=CBS News |date=2009-04-29 |access-date=2010-11-03 |archive-date=2011-08-05 |archive-url=https://web.archive.org/web/20110805043811/https://www.cbsnews.com/stories/2009/04/29/earlyshow/main4976805.shtml |url-status=live }} He recovered, and a bronze statue has been erected in his honor.{{cite web|url=https://www.mirror.co.uk/news/uk-news/statue-erected-of-first-boy-in-world-408563|title=Statue erected of first boy in world who caught swine flu|publisher=Mirror|website=mirror.co.uk|access-date=2009-04-25|archive-date=2014-05-22|archive-url=https://web.archive.org/web/20140522075428/https://www.mirror.co.uk/news/uk-news/statue-erected-of-first-boy-in-world-408563|url-status=live}} 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.{{cite news

|url=https://www.theguardian.com/world/2014/oct/28/ebola-virus-guinea-first-victim-patient-zero

|title=Finding Ebola's 'patient zero'

|newspaper=The Guardian

|access-date=28 November 2014

|date=2014-10-28

|last1=Beukes

|first1=Suzanne

|archive-date=2014-12-19

|archive-url=https://web.archive.org/web/20141219224429/https://www.theguardian.com/world/2014/oct/28/ebola-virus-guinea-first-victim-patient-zero

|url-status=live

}}

• 51-year-old Jesus Lujan was the index case of the 1924 Los Angeles pneumonic plague outbreak which killed 33.{{cite book |last=Feldinger |first=Frank |url=http://archive.org/details/slightepidemicgo0000feld |title=A slight epidemic : the government cover-up of black plague in Los Angeles : what happened and why it matters |date=2008 |publisher=Los Angeles, CA : Silver Lake Pub. |isbn=978-1-56343-885-1 |pages=124–130}}
• There are many known "patient zeros" across the world for the COVID-19 pandemic, 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.{{cite web|url=https://www.foxla.com/news/im-back-in-action-one-of-the-first-americans-who-contracted-covid-19-speaks-about-his-recovery|title="I'm back in action," One of the first Americans who contracted COVID-19 speaks about his recovery|date = 13 March 2021}}
• 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.{{cite web|url=https://www.bbc.com/future/article/20200221-coronavirus-the-harmful-hunt-for-covid-19s-patient-zero|title=Who is 'patient zero' in the coronavirus outbreak?|first=Fernando|last=Duarte|website=www.bbc.com|date=24 February 2020 }}

The term is used to identify the first computer or user to be infected with malware on a network, which then infected other systems.{{cite news|title=Search for patient zero: uncovering malware infection at the source|url=https://www.infosecurity-magazine.com/news/search-for-patient-zero-uncovering-malware/|access-date=31 March 2017|work=Infosecurity Magazine|date=10 July 2012|quote="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."|archive-date=31 March 2017|archive-url=https://web.archive.org/web/20170331204928/https://www.infosecurity-magazine.com/news/search-for-patient-zero-uncovering-malware/|url-status=live}}{{cite news|last1=Savitz|first1=Eric|title=Finding Patient Zero: The Key To Responding To Malware Attacks|url=https://www.forbes.com/sites/ericsavitz/2012/06/05/finding-patient-zero-the-key-to-responding-to-malware-attacks/#1aace8ecf390|access-date=31 March 2017|work=Forbes|date=5 June 2012|quote="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."|archive-date=31 March 2017|archive-url=https://web.archive.org/web/20170331121229/https://www.forbes.com/sites/ericsavitz/2012/06/05/finding-patient-zero-the-key-to-responding-to-malware-attacks/#1aace8ecf390|url-status=live}}

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.{{cite news |url=https://www.cnn.com/2014/10/20/politics/lewinsky-cyber-bullying/index.html |title=Lewinsky makes emotional plea to end cyberbullying |last=Merica |first=Dan |date=October 21, 2014 |publisher=CNN |access-date=October 22, 2014 |archive-date=October 22, 2014 |archive-url=https://web.archive.org/web/20141022080457/https://www.cnn.com/2014/10/20/politics/lewinsky-cyber-bullying/index.html |url-status=live }}

{{portal|Medicine}}

• {{annotated link|Proband}}
• {{annotated link|Misconceptions about HIV/AIDS}}
• Scapegoating

{{Reflist}}

• {{cite web |url=https://www.orgnet.com/contagion.html |archive-url=https://archive.today/20130130194236/http://www.orgnet.com/contagion.html |url-status=dead |archive-date=30 January 2013 |title=Mapping the Spread of Viruses / Contagions via Contact Tracing |publisher=Orgnet |website=orgnet.com |access-date=2010-11-03 }}
• [https://www.nybooks.com/articles/4227 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].
• "[https://www.radiolab.org/story/patient-zero-updated/ Patient Zero - Updated]". Radiolab. Season 13, Episode 3.

{{Concepts in infectious disease}}

{{Authority control}}

Category:Epidemiology

Category:Biological hazards