Superspreading event
A superspreading event (SSEV) is an event in which an
Some cases of superspreading conform to the
SSEVs are shaped by multiple factors including a decline in
Definition
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:[2]
- estimate the effective reproductive number, R, for the disease and population in question;
- construct a stochasticitywithout individual variation;
- 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.[2]
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.[5]
Superspreaders may or may not show any symptoms of the disease.[4][6]
SSEVs can further be classified into 'societal' and 'isolated' events.[7] Funerals have been known to epidemiology as common superspreader events. In particular where funeral rites involve contact with the decedent, funerary transmission may occur.[8] 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.[9]
In April 2020 Jonathan Kay reported in relation to the COVID-19 pandemic:[10]
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.
Factors in transmission
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.[11]
Basic reproductive number
The
R0 = Number of contacts × Shedding potential
Individual reproductive number
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
Co-infections with other pathogens
Studies have shown that men with HIV who are co-infected with at least one other
Lack of herd immunity
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.[11][15] 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.[16] That is not to say that an outbreak can't occur, but it will be limited.[15][17][18]
Superspreaders during outbreaks or pandemics
COVID-19 pandemic: 2020–present
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
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
On March 6, preacher Baldev Singh returned to India after being infected while traveling in
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]
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
On 30 July 2021, it came to light that a Peruvian man, resident of
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
SARS outbreak: 2003
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.[47]
In another case during this same outbreak, a 54-year-old male was admitted to a hospital with coronary heart disease, chronic
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."[48]
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.[5]
Measles outbreak: 1989
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.[49]
Typhoid fever
It has been found that Salmonella typhi persists in infected mice
See also
- Amoy_Gardens#SARS_outbreak
- Compartmental models in epidemiology – Type of mathematical model used for infectious diseases
- Disease outbreak – Sudden increase in occurrences of a disease
- Index case – First documented patient in the population of an epidemiological investigation
- Pandemic – Widespread, often global, epidemic of severe infectious disease
- Scale-free network – A model in which most people spread an infection to few people, but a few people spread infection to many
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External links
- World Health Organisation (WHO) – authoritative source of information about global health issues
- Past pandemics that ravaged Europe at the BBC
- Influenza pandemic phases at the US Center for Disease Control (CDC)
- European Centre for Disease Prevention and Control (ECDC)
- TED-Education video – How pandemics spread