Superspreading event
A superspreading event (SSEV) is an event in which an infectious disease is spread much more than usual, while an unusually contagious organism infected with a disease is known as a superspreader. In the context of a human-borne illness, a superspreader is an individual who is more likely to infect others, compared with a typical infected person. Such superspreaders are of particular concern in epidemiology.
Some cases of superspreading conform to the 80/20 rule,[1] where approximately 20% of infected individuals are responsible for 80% of transmissions, although superspreading can still be said to occur when superspreaders account for a higher or lower percentage of transmissions.[2] In epidemics with such superspreader events, the majority of individuals infect relatively few secondary contacts. The degree to which superspreading contributes to an epidemic is often quantified by the t20 metric, which denotes the proportion of infections attributable to the most infectious 20% of the population.[3]
SSEVs are shaped by multiple factors including a decline in herd immunity, nosocomial infections, virulence, viral load, misdiagnosis, airflow dynamics, immune suppression, and co-infection with another pathogen.[4]
Superspreaders during outbreaks or pandemics[edit]
COVID-19 pandemic: 2020–present[edit]
Several factors are identified as contributing to superspreading events with COVID-19: closed spaces with poor ventilation, crowds, and close contact settings ("three Cs").[19]
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[20] or 70[21] 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.[21] 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."[21] On 21 February, the first death was reported.[22] 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.[23] 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.[24]
A two-day leadership conference for the American biotechnology company Biogen was held at the Mariott 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.[25] A genetic analysis study[26] 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,[25] 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.[27][28]
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,[29] accounting for more than half of SARS-CoV2 coronavirus cases in the state during early March 2020.[30] 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.[31][32]
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.[33] Fearing an outbreak, India's government instituted a local quarantine on 27 March 2020, affecting 40,000 residents from 20 villages.[34] 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.[33][35]
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.
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.[36]
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.[37]
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.[38] By October 7, the Federal Emergency Management Agency memo revealed that 34 White House staff members, housekeepers, and other contacts had contracted the virus.[39]
Public health experts have said that the 2021 United States Capitol attack was a potential COVID-19 superspreading event.[40] 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.[40]
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.[41] 24 days later, the Peruvian man died of a severe pneumonia, being the first death of the Delta variant in Spain.[42]
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.[43][44][45]
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.[46]