Superspreading event

Although loose definitions of superspreader events exist, some effort has been made at defining what qualifies as a superspreader event (SSEV). Lloyd-Smith et al. (2005) define a protocol to identify a superspreader event as follows:

1. estimate the effective reproductive number, R, for the disease and population in question;
2. construct a Poisson distribution with mean R, representing the expected range of Z due to stochasticity without individual variation;
3. define an SSEV as any infected person who infects more than Z⁽ⁿ⁾ others, where Z⁽ⁿ⁾ is the nth percentile of the Poisson(R) distribution.

This protocol defines a 99th-percentile SSEV as a case which causes more infections than would occur in 99% of infectious histories in a homogeneous population.

During the SARS-CoV-1 2002–2004 SARS outbreak from China, epidemiologists defined a superspreader as an individual with at least eight transmissions of the disease.{{cite journal | vauthors = Shen Z, Ning F, Zhou W, He X, Lin C, Chin DP, Zhu Z, Schuchat A | display-authors = 6 | title = Superspreading SARS events, Beijing, 2003 | journal = Emerging Infectious Diseases | volume = 10 | issue = 2 | pages = 256–260 | date = February 2004 | pmid = 15030693 | pmc = 3322930 | doi = 10.3201/eid1002.030732 }}

Superspreaders may or may not show any symptoms of the disease.{{cite book| vauthors = Wiley DC, Cory AC |title=Encyclopedia of School Health|date=2013|publisher=Sage|location=Los Angeles, CA|isbn=978-1412996006 |quote=Historically, one of the most famous examples of super-spreading was that of Mary Mallon, better known as Typhoid Mary, who infected many contacts, several of whom died, through food she prepared and consequently contaminated, even thought she did not show symptoms. }}

SSEVs can further be classified into 'societal' and 'isolated' events.{{cite journal | vauthors = Majra D, Benson J, Pitts J, Stebbing J | title = SARS-CoV-2 (COVID-19) superspreader events | journal = The Journal of Infection | volume = 82 | issue = 1 | pages = 36–40 | date = January 2021 | pmid = 33245943 | pmc = 7685932 | doi = 10.1016/j.jinf.2020.11.021 }} Funerals have been known to epidemiology as common superspreader events. In particular where funeral rites involve contact with the decedent, funerary transmission may occur.{{cite book | vauthors = von Csefalvay C | chapter = Chapter 2: Simple compartmental models: The bedrock of mathematical epidemiology |date= January 2023 | title =Computational Modeling of Infectious Disease |pages=19–91 | veditors = von Csefalvay C |publisher=Academic Press |language=en |doi=10.1016/b978-0-32-395389-4.00011-6 |isbn=978-0-323-95389-4 }} The International Red Cross proposed the practices now known as "safe and dignified burials" during the Western African Ebola virus epidemic to reduce funerary transmission.{{cite journal | vauthors = Sikakulya FK, Ilumbulumbu MK, Djuma SF, Bunduki GK, Sivulyamwenge AK, Jones MK | title = Safe and dignified burial of a deceased from a highly contagious infectious disease ebolavirus: Socio-cultural and anthropological implications in the Eastern DR Congo | journal = One Health | volume = 13 | pages = 100309 | date = December 2021 | pmid = 34458545 | pmc = 8379334 | doi = 10.1016/j.onehlt.2021.100309 }}

In April 2020 Jonathan Kay reported in relation to the COVID-19 pandemic:{{cite news | vauthors = Kay J |title=It's not the size of the event, but the behaviour that matters |url=https://nationalpost.com/opinion/jonathan-kay-on-covid-19-its-not-the-size-of-the-event-but-behaviour-that-matters |publisher=National Post, a division of Postmedia Network Inc |date=30 April 2020}}

{{cquote|Putting aside hospitals, private residences and old-age homes, almost all of these superspreader events (SSEVs) took place in the context of (1) parties, (2) face-to-face professional networking events and meetings, (3) religious gatherings, (4) sports events, (5) meat-processing facilities, (6) ships at sea, (7) singing groups, and, yes, (8) funerals.}}

Image:Herd immunity.svg

Superspreaders have been identified who excrete a higher than normal number of pathogens during the time they are infectious. This causes their contacts to be exposed to higher viral/bacterial loads than would be seen in the contacts of non-superspreaders with the same duration of exposure.Kenneth J. Rothman, Sander Greenland, and Timothy L. Lash. Modern Epidemiology, 3rd Edition. 2008. p. 561. Lippincott, Williams & Wilkins. Philadelphia.

The basic reproduction number R₀ is the average number of secondary infections caused by a typical infective person in a totally susceptible population. The basic reproductive number is found by multiplying the average number of contacts by the average probability that a susceptible individual will become infected, which is called the shedding potential.

{{math|1=R₀ = Number of contacts × Shedding potential}}

The individual reproductive number represents the number of secondary infections caused by a specific individual during the time that individual is infectious. Some individuals have significantly higher than average individual reproductive numbers and are known as superspreaders. Through contact tracing, epidemiologists have identified superspreaders in measles, tuberculosis, rubella, monkeypox, smallpox, Ebola hemorrhagic fever and SARS.{{cite journal | vauthors = De Serres G, Markowski F, Toth E, Landry M, Auger D, Mercier M, Bélanger P, Turmel B, Arruda H, Boulianne N, Ward BJ, Skowronski DM | display-authors = 6 | title = Largest measles epidemic in North America in a decade--Quebec, Canada, 2011: contribution of susceptibility, serendipity, and superspreading events | journal = The Journal of Infectious Diseases | volume = 207 | issue = 6 | pages = 990–998 | date = March 2013 | pmid = 23264672 | doi = 10.1093/infdis/jis923 | doi-access = free }}

Studies have shown that men with HIV who are co-infected with at least one other sexually transmitted disease, such as gonorrhea, hepatitis C, and herpes simplex 2 virus, have a higher HIV shedding rate than men without co-infection. This shedding rate was calculated in men with similar HIV viral loads. Once treatment for the co-infection has been completed, the HIV shedding rate returns to levels comparable to men without co-infection.{{cite journal | vauthors = Cohen MS, Hoffman IF, Royce RA, Kazembe P, Dyer JR, Daly CC, Zimba D, Vernazza PL, Maida M, Fiscus SA, Eron JJ | display-authors = 6 | title = Reduction of concentration of HIV-1 in semen after treatment of urethritis: implications for prevention of sexual transmission of HIV-1. AIDSCAP Malawi Research Group | journal = Lancet | volume = 349 | issue = 9069 | pages = 1868–1873 | date = June 1997 | pmid = 9217758 | doi = 10.1016/s0140-6736(97)02190-9 | s2cid = 9723768 }}{{cite journal | vauthors = Winter AJ, Taylor S, Workman J, White D, Ross JD, Swan AV, Pillay D | title = Asymptomatic urethritis and detection of HIV-1 RNA in seminal plasma | journal = Sexually Transmitted Infections | volume = 75 | issue = 4 | pages = 261–263 | date = August 1999 | pmid = 10615314 | pmc = 1758225 | doi = 10.1136/sti.75.4.261 }}

Herd immunity, or herd effect, refers to the indirect protection that immunized community members provide to non-immunized members in preventing the spread of contagious disease. The greater the number of immunized individuals, the less likely an outbreak can occur because there are fewer susceptible contacts. In epidemiology, herd immunity is known as a dependent happening because it influences transmission over time. As a pathogen that confers immunity to the survivors moves through a susceptible population, the number of susceptible contacts declines. Even if susceptible individuals remain, their contacts are likely to be immunized, preventing any further spread of the infection.{{cite journal | vauthors = Fine PE | title = Herd immunity: history, theory, practice | journal = Epidemiologic Reviews | volume = 15 | issue = 2 | pages = 265–302 | year = 1993 | pmid = 8174658 | doi = 10.1093/oxfordjournals.epirev.a036121 }} The proportion of immune individuals in a population above which a disease may no longer persist is the herd immunity threshold. Its value varies with the virulence of the disease, the efficacy of the vaccine, and the contact parameter for the population.{{cite book |veditors=Jamison DT, Breman JG, Measham AR |title=Priorities in Health: Disease Control Priorities Companion Volume |publisher=World Bank Publications |year=2006 |chapter=Chapter 4: Cost-Effective Strategies for the Excess Burden of Disease in Developing Countries
Section: Vaccine-preventable Diseases |chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK10258/#A151 |isbn=0-8213-6260-7}} That is not to say that an outbreak can't occur, but it will be limited.{{cite journal | vauthors = Yeung LF, Lurie P, Dayan G, Eduardo E, Britz PH, Redd SB, Papania MJ, Seward JF | display-authors = 6 | title = A limited measles outbreak in a highly vaccinated US boarding school | journal = Pediatrics | volume = 116 | issue = 6 | pages = 1287–1291 | date = December 2005 | pmid = 16322148 | doi = 10.1542/peds.2004-2718 | s2cid = 27236339 }}{{cite journal | vauthors = Fine P, Eames K, Heymann DL | title = "Herd immunity": a rough guide | journal = Clinical Infectious Diseases | volume = 52 | issue = 7 | pages = 911–916 | date = April 2011 | pmid = 21427399 | doi = 10.1093/cid/cir007 | doi-access = free }}

Several factors are identified as contributing to superspreading events with COVID-19: closed spaces with poor ventilation, crowds, and close contact settings ("three Cs").{{cite journal | vauthors = Enserink M, Kupferschmidt K, Desai N | date = February 2020 | title = The science of superspreading. | journal = Science Magazine |url = https://vis.sciencemag.org/covid-clusters/ }}

The South Korean spread of confirmed cases of SARS-CoV-2 infection jumped suddenly starting on 19–20 February 2020. On 19 February, the number of confirmed cases increased by 20. On 20 February, 58{{cite news |title=코로나19 확진자 104명...31번 환자 연관 신천지교회 대남병원서만 확진자 58명, 1명 사망 |url=http://m.getnews.co.kr/view.php?ud=2020022021135849202aaae0046f_16 |access-date=16 March 2020 |work=글로벌경제신문 |date=20 February 2020 |language=ko}} or 70{{cite news | vauthors = Shin H, Cha S | title= 'Like a zombie apocalypse': Residents on edge as coronavirus cases surge in South Korea |trans-title = | date= 2020-02-20 |agency=Thomson Reuters | url= https://www.reuters.com/article/us-china-health-southkorea-cases/like-a-zombie-apocalypse-residents-on-edge-as-coronavirus-cases-surge-in-south-korea-idUSKBN20E04F |access-date=2020-02-20 |archive-url= https://archive.today/20200220113906/https://www.reuters.com/article/us-china-health-southkorea-cases/like-a-zombie-apocalypse-residents-on-edge-as-coronavirus-cases-surge-in-south-korea-idUSKBN20E04F |archive-date= 2020-02-20 |url-status=live |url-access = }} new cases were confirmed, giving a total of 104 confirmed cases, according to the Centers for Disease Control and Prevention Korea (KCDC). According to Reuters, KCDC attributed the sudden jump to 70 cases linked to "Patient 31", who had participated in a gathering in Daegu at the Shincheonji Church of Jesus the Temple of the Tabernacle of the Testimony. On 20 February, the streets of Daegu were empty in reaction to the Shincheonji outbreak. A resident described the reaction, stating "It's like someone dropped a bomb in the middle of the city. It looks like a zombie apocalypse." On 21 February, the first death was reported.{{Cite web|url=https://www.nbcnews.com/health/health-news/south-korea-reports-first-coronavirus-death-infections-linked-church-rise-n1139821 |title=South Korea reports first coronavirus death as infections linked to church rise|website=NBC News|date=20 February 2020 |language=en|access-date=2020-02-21}} According to the mayor of Daegu, the number of suspected cases as of 21 February is 544 among 4,400 examined followers of the church.{{cite web |title=신천지 관련 확진자 76명으로 늘어...대구 교인 의심자만 544명 |publisher=Chosun.com |date=21 February 2020 |url=https://news.chosun.com/site/data/html_dir/2020/02/21/2020022101558.html}} Later in the outbreak, in May, a 29-year-old man visited several Seoul nightclubs in one night and resulted in accumulated infections of at least 79 other people.{{cite web |url= http://nwww.koreaherald.com/view.php?ud=20200511000575 |title= Itaewon cluster caseload rises to 79: Nation adds 35 new cases, 20 in Seoul |author= Park Han-na |date= 11 May 2020 |website= The Korea Herald |access-date= 11 May 2020 |archive-url=https://web.archive.org/web/20200516111911/http://nwww.koreaherald.com/view.php?ud=20200511000575 |archive-date=16 May 2020 |url-status=live}}

A two-day leadership conference for the American biotechnology company Biogen was held at the Marriott Long Wharf Hotel in Boston, Massachusetts, from 26 to 28 February 2020. 99 of the 175 executives in attendance later tested positive for COVID-19, and the hotel was shut down days later.{{Cite news | vauthors = Wines M |title=What Happens When a Superspreader Event Keeps Spreading |work=The New York Times |date=12 December 2020 |url=https://www.nytimes.com/2020/12/11/us/biogen-conference-covid-spread.html |access-date=9 November 2022}} A genetic analysis study{{cite journal | vauthors = Lemieux JE, Siddle KJ, Shaw BM, Loreth C, Schaffner SF, Gladden-Young A, Adams G, Fink T, Tomkins-Tinch CH, Krasilnikova LA, DeRuff KC, Rudy M, Bauer MR, Lagerborg KA, Normandin E, Chapman SB, Reilly SK, Anahtar MN, Lin AE, Carter A, Myhrvold C, Kemball ME, Chaluvadi S, Cusick C, Flowers K, Neumann A, Cerrato F, Farhat M, Slater D, Harris JB, Branda JA, Hooper D, Gaeta JM, Baggett TP, O'Connell J, Gnirke A, Lieberman TD, Philippakis A, Burns M, Brown CM, Luban J, Ryan ET, Turbett SE, LaRocque RC, Hanage WP, Gallagher GR, Madoff LC, Smole S, Pierce VM, Rosenberg E, Sabeti PC, Park DJ, MacInnis BL | display-authors = 6 | title = Phylogenetic analysis of SARS-CoV-2 in Boston highlights the impact of superspreading events | journal = Science | volume = 371 | issue = 6529 | date = February 2021 | pmid = 33303686 | pmc = 7857412 | doi = 10.1126/science.abe3261 }} published later the same year estimated the spread at the conference eventually resulted in 1.9% of U.S. coronavirus cases, or as many as 300,000 people. The event was the subject of a New York Times article, and substantial criticism was leveled at Biogen for its role in the incident.

Between 27 February and 1 March, a Tablighi Jamaat event at Masjid Jamek, Seri Petaling in Kuala Lumpur, Malaysia attended by approximately 16,000 people resulted in a major outbreak across the country. By May 16, 3,348 COVID-19 cases - 48% of Malaysia's total at the time - were linked to the event, and with approximately 10% of attendees visiting from overseas, the event resulted in the virus spreading across Southeast Asia. Cases in Cambodia, Indonesia, Vietnam, Brunei, the Philippines and Thailand were traced back to the mosque gathering.{{cite journal | vauthors = Che Mat NF, Edinur HA, Abdul Razab MK, Safuan S | title = A single mass gathering resulted in massive transmission of COVID-19 infections in Malaysia with further international spread | journal = Journal of Travel Medicine | volume = 27 | issue = 3 | date = May 2020 | pmid = 32307549 | pmc = 7188142 | doi = 10.1093/jtm/taaa059 | doi-access = free }}{{Cite web|date=2020-03-18|title=Wonder how dangerous a gathering can be? Here's how one event sparked hundreds of coronavirus cases across Asia|url=https://www.abc.net.au/news/2020-03-19/coronavirus-spread-from-malaysian-event-to-multiple-countries/12066092|access-date=2020-12-29|website=www.abc.net.au|language=en-AU}}

In New York, a lawyer contracted the illness then spread it to at least twenty other individuals in his community in New Rochelle, creating a cluster of cases that quickly passed 100,{{cite web |author=Sheena Jones and Christina Maxouris |title=New York officials traced more than 50 coronavirus cases back to one attorney |url=https://www.cnn.com/2020/03/11/us/new-rochelle-attorney-containment-area/index.html |website=CNN |date=11 March 2020 |access-date=13 March 2020}} accounting for more than half of SARS-CoV2 coronavirus cases in the state during early March 2020.{{cite web |author=Eric Levenson and Kristina Sgueglia |title=New York creates 'containment zone' around cluster of coronavirus cases in New Rochelle |url=https://www.cnn.com/2020/03/10/us/new-rochelle-coronavirus/index.html |website=CNN |date=10 March 2020 |access-date=13 March 2020}} For comparison, the basic reproduction number of the virus, which is the average number of additional people that a single case will infect without any preventative measures, is between 1.4 and 3.9.{{cite journal | vauthors = Li Q, Guan X, Wu P, Wang X, Zhou L, Tong Y, Ren R, Leung KS, Lau EH, Wong JY, Xing X, Xiang N, Wu Y, Li C, Chen Q, Li D, Liu T, Zhao J, Liu M, Tu W, Chen C, Jin L, Yang R, Wang Q, Zhou S, Wang R, Liu H, Luo Y, Liu Y, Shao G, Li H, Tao Z, Yang Y, Deng Z, Liu B, Ma Z, Zhang Y, Shi G, Lam TT, Wu JT, Gao GF, Cowling BJ, Yang B, Leung GM, Feng Z | display-authors = 6 | title = Early Transmission Dynamics in Wuhan, China, of Novel Coronavirus-Infected Pneumonia | journal = The New England Journal of Medicine | volume = 382 | issue = 13 | pages = 1199–1207 | date = March 2020 | pmid = 31995857 | pmc = 7121484 | doi = 10.1056/NEJMoa2001316 | doi-access = free }}{{cite journal | vauthors = Riou J, Althaus CL | title = Pattern of early human-to-human transmission of Wuhan 2019 novel coronavirus (2019-nCoV), December 2019 to January 2020 | journal = Euro Surveillance | volume = 25 | issue = 4 | date = January 2020 | pmid = 32019669 | pmc = 7001239 | doi = 10.2807/1560-7917.ES.2020.25.4.2000058 }}

On March 6, preacher Baldev Singh returned to India after being infected while traveling in Italy and Germany. He subsequently died, becoming the first coronavirus fatality in the State of Punjab. Testing revealed that he'd infected 26 locals, including 19 relatives, while tracing discovered that he'd had direct contact with more than 550 people.{{Cite news|url=https://timesofindia.indiatimes.com/city/ludhiana/now-polices-moose-wala-song-blames-1st-casualty/articleshow/74859668.cms |title=Now, police's Moose Wala song blames 1st causality |date=2020-03-28|website=The Times of India|access-date=2020-08-17|language=en}} Fearing an outbreak, India's government instituted a local quarantine on 27 March 2020, affecting 40,000 residents from 20 villages.{{Cite news|url=https://www.bbc.com/news/world-asia-india-52061915 |title=India 'super spreader' quarantines 40,000 people|date=2020-03-27|work=BBC News|access-date=2020-03-27|language=en-GB}} Initial reports claimed that Baldev Singh had ignored self-quarantine orders, and police collaborated with singer Sidhu Moose Wala to release a rap music video blaming the dead man for bringing the virus to Punjab. But Baldev Singh's fellow travelers insisted that no such order had been given, leading to accusations that local authorities had scapegoated him to avoid scrutiny of their own failures.{{Cite news|url=https://timesofindia.indiatimes.com/city/chandigarh/vilification-of-baldev-based-on-falsehood/articleshow/74882091.cms |title=Vilification of Baldev based on falsehood |date=2020-03-30|website=The Times of India|access-date=2020-08-17|language=en}}

A Tablighi Jamaat religious congregation that took place in Delhi's Nizamuddin Markaz Mosque in early March 2020 was a coronavirus super-spreader event, with more than 4,000 confirmed cases and at least 27 deaths linked to the event reported across the country. Over 9,000 missionaries may have attended the congregation, with the majority being from various states of India, and 960 attendees from 40 foreign countries. On 18 April, 4,291 confirmed cases of COVID-19 linked to this event by the Union Health Ministry represented a third of all the confirmed cases of India. Around 40,000 people, including Tablighi Jamaat attendees and their contacts, were quarantined across the country.{{citation needed|date=June 2021}}

On 11 May 2020, it came to light that a worker at a fish processing plant in Tema, Ghana was believed to have infected over 500 other people with COVID-19.{{cite web |author=Bukola Adebayo |title=A worker infected 533 others with coronavirus at a factory in Ghana, president says |url=https://www.cnn.com/2020/05/11/africa/ghana-factory-coronavirus-infection-intl/index.html |website=CNN |date=11 May 2020 |access-date=11 May 2020 |quote=Hundreds of factory workers at a fish processing plant in Ghana have tested positive for the coronavirus, the country's president Nana Akufo-Addo said. All 533 of them contracted the virus from one worker at the factory in the port city of Tema, the president said in his public address to the nation Sunday.}}

As of 18 July 2020, more than one thousand suspected superspreading events had been logged, for example a cluster of 187 people who were infected after eating at a Harper's Restaurant and Brew Pub in East Lansing, Michigan.{{cite news | title='Superspreading' events, triggered by people who may not even know they are infected, propel coronavirus pandemic | vauthors = Cha A | url=https://www.washingtonpost.com/health/2020/07/18/coronavirus-superspreading-events-drive-pandemic/|newspaper=Washington Post | access-date=18 July 2020}}

On 26 September 2020, President Donald Trump announced his Supreme Court Justice nominee, Amy Coney Barrett. The announcement took place at the White House Rose Garden, where around 30 people attentively watched. The outbreak event has since been dubbed a "superspreader" event. Less than a week after the event, Trump himself was diagnosed with SARS-CoV-2, as well as others who attended the Rose Garden event.{{Cite web| vauthors = Says AG |date=2020-11-02|title=Genomic sequence of the White House "superspreader" event|url=https://www.news-medical.net/news/20201102/Genomic-sequence-of-the-White-House-superspreader-event.aspx|access-date=2021-03-03|website=News-Medical.net|language=en}} By October 7, the Federal Emergency Management Agency memo revealed that 34 White House staff members, housekeepers, and other contacts had contracted the virus.{{Cite news|date=2020-10-10|title=White House hosted Covid 'superspreader' event, says Dr Fauci|language=en-GB|work=BBC News|url=https://www.bbc.com/news/election-us-2020-54487154|access-date=2021-03-03}}

Public health experts have said that the 2021 United States Capitol attack was a potential COVID-19 superspreading event.{{Cite news| vauthors = Villegas P, Chason R, Knowles H | date = 8 January 2021 |title=Storming of Capitol was textbook potential coronavirus superspreader, experts say|newspaper=The Washington Post|url=https://www.washingtonpost.com/health/2021/01/08/capitol-coronavirus/|access-date=January 8, 2021}} Few members of the crowd attacking the Capitol wore face coverings, with many coming from out of town, and few of the rioters were immediately detained and identified.

On 30 July 2021, it came to light that a Peruvian man, resident of Córdoba, Argentina, brought the Delta variant of COVID-19 after travelling to Spain, but he did not quarantine himself, infecting 17 relatives and putting in isolation over 800 other people. He and other three people got arrested for disease propagation.{{cite web | vauthors = Ámbito I |title=A Peruvian man ignored Delta-variant positive, reunited with relatives and installed a "epidemiological bomb" on his town|url=https://www.ambito.com/informacion-general/covid-19/variante-delta-cordoba-ya-hay-mas-800-personas-aisladas-n5237191|website=Ámbito |access-date=9 August 2021 |quote= The Health's Ministry of Córdoba is intensively trying to detect and isolate that came in contact with the first Delta-variant infected in the province, that infected 17 relatives and threatened over more of 800 people}} 24 days later, the Peruvian man died of a severe pneumonia, being the first death of the Delta variant in Spain.{{cite web | vauthors = Perfil I |title=First death for Delta variant of Argentina: patient zero Peruvian man who infected his whole town died today |url= https://www.perfil.com/noticias/actualidad/primera-muerte-por-delta-en-argentina-fallecio-el-paciente-cero-de-cordoba.phtml |website= Perfil|date=22 August 2021 |access-date=23 August 2021 |quote= The same Peruvian man that started an "epidemiological bomb" on his town died from a severe pneumonia.}}

On 26 November 2021, Scatec ASA, a Norwegian company specializing in renewable energy systems, held a Christmas party in Oslo, Norway attended by 120 people, all of whom were fully vaccinated against COVID-19 and tested negative for COVID-19 prior to the party being held. One person who attended the party had recently returned from South Africa, the epicenter of the SARS-CoV-2 Omicron variant outbreak and a country where the company has a solar panel project. It was later found that the attendee from South Africa had been infected with the Omicron variant. More than half of the party's attendees have since tested positive for COVID-19 and of those attendees, at least 13 of them were confirmed to have the variant.{{Cite news| vauthors = Hinshaw D |date=2021-12-03|title=Omicron Cases at Norway Christmas Party Provide Clues on New Variant's Spread|language=en-US|work=The Wall Street Journal|url=https://www.wsj.com/articles/omicron-cases-at-norway-christmas-party-provide-clues-on-new-variants-spread-11638554033|access-date=2021-12-03|issn=0099-9660}}{{Cite news| vauthors = Fouche G, Adomaitis N |date=2021-12-03|title=Omicron outbreak at Norway Christmas party is biggest outside S. Africa -authorities|language=en|work=Reuters|url=https://www.reuters.com/world/europe/omicron-outbreak-norway-christmas-party-is-biggest-outside-s-africa-authorities-2021-12-03/|access-date=2021-12-03}}{{Cite news| vauthors = Erdbrink T, Libell HP, Frost N, Yoon J |date=2021-12-03|title=A Christmas party in Norway becomes a possible Omicron-spreading event, and other international news.|language=en-US|work=The New York Times|url=https://www.nytimes.com/2021/12/03/world/omicron-norway-christmas-party.html|access-date=2021-12-03|issn=0362-4331}}

On 3 April 2022, the Gridiron Dinner in Washington D.C. led to at least 67 people testing positive for COVID-19, including three members of the Cabinet of Joe Biden: Merrick Garland, Gina Raimondo, and Tom Vilsack.{{Cite web|url=https://www.nbcnews.com/politics/politics-news/67-attendees-test-positive-covid-high-profile-dc-dinner-rcna23763|title = 72 people at high-profile D.C. Dinner test positive for Covid|website = NBC News| date=10 April 2022 }}

In the later years of the COVID-19 pandemic, concern has emerged that any large gatherings that take place without COVID-19 mitigation tools such as respirator masks or air filtration have the potential to become superspreader events.{{Cite web |last=Parramore |first=Lynn |date=May 31, 2024 |title=From Long COVID Odds to Lost IQ Points: Ongoing Threats You Don't Know About |url=https://www.ineteconomics.org/perspectives/blog/from-long-covid-odds-to-lost-iq-points-ongoing-threats-you-dont-know-about |url-status=live |archive-url=https://web.archive.org/web/20250128125324/https://www.ineteconomics.org/perspectives/blog/from-long-covid-odds-to-lost-iq-points-ongoing-threats-you-dont-know-about |archive-date=January 28, 2025 |access-date=February 17, 2025 |website=Institute for New Economic Thinking}}{{Cite web |date=February 5, 2024 |title=What Constitutes a 'Superspreader Event'? |url=https://health.clevelandclinic.org/superspreader-events |access-date=2025-02-17 |website=Cleveland Clinic |language=en}}{{Cite web |last=Frieden |first=Joyce |date=August 28, 2024 |title=An Unwelcome Souvenir From the Democratic National Convention: COVID |url=https://www.medpagetoday.com/infectiousdisease/covid19/111709 |url-status=live |archive-url=https://web.archive.org/web/20240915201931/https://www.medpagetoday.com/infectiousdisease/covid19/111709 |archive-date=September 15, 2024 |access-date=February 17, 2025 |website=MedPage Today}}{{Cite web |last=Vales |first=Frank |date=2023 |title=COVID-19 Is Still a Thing in 2023, and Here's Why You Should Care |url=https://engage.youth.gov/resources/covid-19-still-thing-2023-and-heres-why-you-should-care |url-status=dead |archive-url=https://web.archive.org/web/20250111181137/https://engage.youth.gov/resources/covid-19-still-thing-2023-and-heres-why-you-should-care |archive-date=January 11, 2025 |access-date=February 17, 2025 |website=Youth Engaged 4 Change}} Schools, concerts, grocery stores, and conventions or conferences may become high-risk sites for SARS-CoV-2 infection. In 2024, both the Democratic National Convention and Republican National Convention in the United States may have caused a measurable rise in cases among attendees and in surrounding localities. Due to the evolution of many novel Omicron subvariants that are highly divergent from both the ancestral SARS-CoV-2 and the original Omicron variant since its emergence in 2021, immunity from prior infection is of limited use in preventing reinfection without other anti-COVID-19 measures. The risk of contracting COVID-19 at superspreader events may therefore prevent seniors or people with conditions of the immune system from performing normal public activities.{{Cite magazine |last=Ducharme |first=Jamie |date=2024-03-27 |title=COVID-Cautious Americans Feel Abandoned |url=https://time.com/6960789/covid-19-cautious-americans/ |access-date=2025-02-17 |magazine=TIME |language=en}} Respirator masks such as those adhering to the United States N95 standard slow COVID-19 transmission, reduce the odds of testing positive, and protect people infected with SARS-CoV-2 from transmitting the virus to others, even in the presence of highly transmissible variants such as Delta or Omicron.{{Cite journal |last=Andrejko |first=Kristin L. |date=2022 |title=Effectiveness of Face Mask or Respirator Use in Indoor Public Settings for Prevention of SARS-CoV-2 Infection — California, February–December 2021 |url=https://www.cdc.gov/mmwr/volumes/71/wr/mm7106e1.htm |journal=MMWR. Morbidity and Mortality Weekly Report |language=en-us |volume=71 |issue=6 |pages=212–216 |doi=10.15585/mmwr.mm7106e1 |pmid=35143470 |issn=0149-2195|pmc=8830622 }}{{Cite journal |last1=Karan |first1=Abraar |last2=Ferguson |first2=Jessica |last3=Salinas |first3=Jorge L. |date=January 2023 |title=Lack of severe acute respiratory coronavirus virus 2 (SARS-CoV-2) transmission from a healthcare worker to a cohort of immunosuppressed patients during the SARS-CoV-2 omicron variant surge, California, 2022 |journal=Infection Control & Hospital Epidemiology |language=en |volume=44 |issue=1 |pages=156–157 |doi=10.1017/ice.2022.175 |pmid=35794737 |issn=0899-823X|pmc=9273728 }}{{Cite journal |last1=Ngonghala |first1=Calistus N. |last2=Taboe |first2=Hemaho B. |last3=Safdar |first3=Salman |last4=Gumel |first4=Abba B. |date=2023-02-01 |title=Unraveling the dynamics of the Omicron and Delta variants of the 2019 coronavirus in the presence of vaccination, mask usage, and antiviral treatment |journal=Applied Mathematical Modelling |volume=114 |pages=447–465 |doi=10.1016/j.apm.2022.09.017 |pmid=36281307 |issn=0307-904X|pmc=9581714 }}

File:Guangdong in China (+all claims hatched).svg

The first cases of SARS occurred in mid-November 2002 in the Guangdong Province of China. This was followed by an outbreak in Hong Kong in February 2003. A Guangdong Province doctor, Liu Jianlun, who had treated SARS cases there, had contracted the virus and was symptomatic. Despite his symptoms, he traveled to Hong Kong to attend a family wedding. He stayed on the ninth floor of the Metropole Hotel in Kowloon, infecting 16 other hotel guests also staying on that floor. The guests then traveled to Canada, Singapore, Taiwan, and Vietnam, spreading SARS to those locations and transmitting what became a global epidemic.{{cite web|url=http://www.scielosp.org/pdf/bwho/v81n8/v81n8a14.pdf |title=How SARS changed the world in less than six months|access-date=February 4, 2016 |url-status=dead |archive-url=https://web.archive.org/web/20120405125444/http://www.scielosp.org/pdf/bwho/v81n8/v81n8a14.pdf |archive-date=April 5, 2012 }}

In another case during this same outbreak, a 54-year-old male was admitted to a hospital with coronary heart disease, chronic kidney failure and type II diabetes mellitus. He had been in contact with a patient known to have SARS. Shortly after his admission he developed fever, cough, myalgia and sore throat. The admitting physician suspected SARS. The patient was transferred to another hospital for treatment of his coronary artery disease. While there, his SARS symptoms became more pronounced. Later, it was discovered he had transmitted SARS to 33 other patients in just two days. He was transferred back to the original hospital where he died of SARS.{{citation needed|date=June 2021}}

In his post-mortem reflection, Low remained puzzled as to the reason for this phenomenon and speculated that "possible explanations for (the superspreaders') enhanced infectivity include the lack of early implementation of infection control precautions, higher load of SCoV, or larger amounts of respiratory secretions."{{cite book |last=Low |first=Donald |author-link=Donald Low |date=2004 |url= https://www.ncbi.nlm.nih.gov/books/NBK92467/ |pages= 63–71 |title=Learning from SARS: Preparing for the Next Disease Outbreak: Workshop Summary|chapter=Sars: Lessons from Toronto |publisher=National Academies Press (US)}}

The SARS outbreak was eventually contained, but not before it caused 8,273 cases and 775 deaths. Within two weeks of the original outbreak in Guangdong Province, SARS had spread to 29 countries.

File:Measles vaccination coverage world.svg worldwide in 2010]]

Measles is a highly contagious, air-borne virus that reappears even among vaccinated populations. In one Finnish town in 1989, an explosive school-based outbreak resulted in 51 cases, several of whom had been previously vaccinated. One child alone infected 22 others. It was noted during this outbreak that when vaccinated siblings shared a bedroom with an infected sibling, seven out of nine became infected as well.{{cite journal | vauthors = Paunio M, Peltola H, Valle M, Davidkin I, Virtanen M, Heinonen OP | title = Explosive school-based measles outbreak: intense exposure may have resulted in high risk, even among revaccinees | journal = American Journal of Epidemiology | volume = 148 | issue = 11 | pages = 1103–1110 | date = December 1998 | pmid = 9850133 | doi = 10.1093/oxfordjournals.aje.a009588 | doi-access = free }}

Typhoid fever is a human-specific disease caused by the bacterium Salmonella typhi. It is highly contagious and becoming resistant to antibiotics.{{cite news|first = Roger | last = Highfield|title=Typhoid is with us to stay|publisher=The Daily Telegraph|date=28 November 2006|url= https://www.telegraph.co.uk/health/healthnews/3345526/Typhoid-is-with-us-to-stay.html |archive-url= https://web.archive.org/web/20110213072928/http://www.telegraph.co.uk/health/healthnews/3345526/Typhoid-is-with-us-to-stay.html |url-status= dead |archive-date= 13 February 2011 |access-date=2015-03-03}} S. typhi is susceptible to creating asymptomatic carriers. The most famous carriers are Mary Mallon, known as Typhoid Mary, from New York City, and Mr. N. the Milker, from Folkestone, England.{{cite journal | vauthors = Mortimer PP | title = Mr N the milker, and Dr Koch's concept of the healthy carrier | journal = Lancet | volume = 353 | issue = 9161 | pages = 1354–1356 | date = April 1999 | pmid = 10218549 | doi = 10.1016/S0140-6736(98)11315-6 | s2cid = 37788256 }} Both were active around the same time. Mallon infected 51 people from 1902 to 1909. Mr. N. infected more than 200 people over 14 years from 1901 to 1915. At the request of health officials, Mr. N. gave up working in food service. Mallon was at first also compliant, choosing other work – but eventually she returned to cooking and caused further outbreaks. She was involuntarily quarantined at Brothers Island in New York, where she stayed until she died in November 1938, aged 69.{{cite journal | vauthors = Marr JS | title = Typhoid Mary | journal = Lancet | volume = 353 | issue = 9165 | pages = 1714 | date = May 1999 | pmid = 10335825 | doi = 10.1016/S0140-6736(05)77031-8 | s2cid = 1482311 }}

It has been found that Salmonella typhi persists in infected mice macrophages that have cycled from an inflammatory state to a non-inflammatory state. The bacteria remain and reproduce without causing further symptoms in the mice, and this helps to explain why carriers are asymptomatic.{{cite journal | vauthors = Ng TM, Monack DM | title = Revisiting caspase-11 function in host defense | journal = Cell Host & Microbe | volume = 14 | issue = 1 | pages = 9–14 | date = July 2013 | pmid = 23870309 | pmc = 3785303 | doi = 10.1016/j.chom.2013.06.009 }}{{cite journal | vauthors = Eisele NA, Ruby T, Jacobson A, Manzanillo PS, Cox JS, Lam L, Mukundan L, Chawla A, Monack DM | display-authors = 6 | title = Salmonella require the fatty acid regulator PPARδ for the establishment of a metabolic environment essential for long-term persistence | journal = Cell Host & Microbe | volume = 14 | issue = 2 | pages = 171–182 | date = August 2013 | pmid = 23954156 | pmc = 3785333 | doi = 10.1016/j.chom.2013.07.010 }}{{cite news| vauthors = Mohan G |title=Typhoid Mary case may be cracked, a century later|newspaper=Los Angeles Times|date=August 14, 2013|url=http://www.latimes.com/science/sciencenow/la-sci-sn-typhoid-mary-20130814-story.html|access-date=2015-03-03}}{{cite news| vauthors = McNeil Jr DG |title= Bacteria study offers clues to Typhoid Mary mystery|newspaper=The New York Times|date=August 26, 2013|url=https://www.nytimes.com/2013/08/27/health/bacteria-study-offers-clues-to-typhoid-mary-mystery.html?_r=0|access-date=2015-03-03}}

{{Portal|Medicine}}

• Amoy Gardens 2003 SARS outbreak
• {{annotated link|Compartmental models in epidemiology}}
• {{annotated link|Disease outbreak}}
• {{annotated link|Index case}}
• {{annotated link|Pandemic}}
• Scale-free network – A model in which most people spread an infection to few people, but a few people spread infection to many

{{Clear}}

{{Reflist}}

{{Wiktionary|superspreading|superspreader}}

• [https://www.who.int/en/ World Health Organization (WHO)] – authoritative source of information about global health issues
• [http://news.bbc.co.uk/2/hi/health/4381924.stm Past pandemics that ravaged Europe] at the BBC
• [https://www.cdc.gov/flu/pandemic/phases.htm Influenza pandemic phases] at the US Center for Disease Control (CDC)
• [http://www.ecdc.europa.eu/ European Centre for Disease Prevention and Control (ECDC)]
• [https://www.youtube.com/user/TEDEducation?feature=watch TED-Education video] – [https://www.youtube.com/watch?v=UG8YbNbdaco How pandemics spread]

{{Concepts in infectious disease}}

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