A common objective unites the world at present - containing the spread of the novel coronavirus and bringing life back to normal.
The process involves information dissemination to the general public, measures to enforce social distancing, and precautions to be taken by people. An important aspect is also to identify patterns and map how the COVID-19 disease is spreading, in order to know just how where interventions can be made to halt it.
A term that is being used in the analysis of the transmission dynamics of the virus is ‘super-spreader’. FIT explains the term and what it means for the COVID-19 pandemic.
What Is a Super-Spreader?
While a strict medical definition is lacking, a super-spreader, as the name suggests, is a person who spreads the disease to more number of people than an average infected person would. In fact, such beings are not limited to humans but are also present among other species.
For instance: A and B get infected by a virus, and let’s say, they are both asymptomatic. Carrying on with their usual routines, A transmits the disease to 10 other people while B causes only 2 secondary cases.
‘A’ could then possibly be a super-spreader.
It is not necessary for all infected individuals to be equally contagious. In fact, the 20/80 rule derived from observational and modelling studies describes this phenomenon: 20% of the individuals within any given population are thought to contribute at least 80% to the transmission potential of a pathogen.
An infectious disease specialist at Yale Medicine, Manisha Juthani, MD told Health,
And not just individuals, even ‘events’ can be called super-spreaders if a sudden surge is witnessed in the cases right after among those who attended them, and others who may have come in contact with them.
Super-Spreaders of the Novel Coronavirus
The World Health Organisation (WHO) does not use ‘super-spreading’ as a technical term and maintains, “We don’t have enough evidence to confirm a case involving a super-spreading event in the COVID-19 outbreak.”
However, certain cases reported from various parts of the world imply a pattern that could fall within the super-spreading category. The WHO does acknowledge that there can be incidents of transmission where a large number of people get infected by a ‘common source’.
The reproductive number for the novel coronavirus – the number of secondary infections generated from one infected individual – is understood to be between 2 and 2.5. But in some cases, this number is higher.
Our understanding of the disease is still evolving, and being certain of a person’s ‘super spreader’ status is difficult. But a few cases where the transmission rate was seen to be higher than 2.6 have been identified as possible super-spreaders:
- A 53-year-old British man in the UK, contracted COVID-19 while at a conference in Singapore. Oblivious to his status, he traveled to France, where he spent several days at a ski chalet. Ultimately, he infected five Britons with the disease and has been linked to at least 11 confirmed cases since then.
- Till mid-February, South Korea had 30 confirmed cases of COVID-19. The 31st case, however, changed everything. ‘Case-31’, as the woman is referred to, had attended church services with over 500 other attendees at each congregation. She potentially infected thousands of people.
- After a party in Westport in Connecticut, the town that didn’t have a single known case of the coronavirus until that day, had at least 85 a few days later.
- In January, reports from Wuhan cited a case of a single patient who infected 14 health care workers.
What Makes a Super-Spreader?
There is no one reason why a particular case becomes a ‘super-spreader’. Multiple factors may be at play, such as the person’s biology, their behavior, environment and degree of contact, and the stage of the disease.
Christl Donnelly, a professor of statistical epidemiology at Imperial College London, told Reuters,
It is also about how much a person travels and how much of the virus a person shreds owing to his/her immune system. People who are extremely tolerant of a pathogen and don’t show symptoms for long may infect other people by moving out and interacting. On the other hand, those with weaker immune systems can permit high virus replication and transmit the virus despite minimising social contact.
Speaking to Health, Manisha Juthani explained, “One theory is that co-infection with another infectious disease at the same time (like if a person is infected with influenza and COVID-19) could make a person more infectious. It is also possible that a particular strain is more infectious or that a super-spreader is shedding more of the infectious agent.”
Super-Spreaders in Previous Outbreaks
The concept of social-spreading is not exclusive to the current COVID-19 pandemic. In fact, the first reported super-spreader can be traced back to the early 20th century. ‘Typhoid Mary’, as she came to be known, reportedly infected at least 51 people with the disease through the food she prepared as a cook.
An article in The Conversation states that super spreaders have been major carriers of disease during the measles outbreak in the US, particularly sick and unvaccinated people who traveled and visited crowded places, transmitting the virus to multiple others.
More recently, the SARS and MARS outbreak also saw such individuals, especially in hospitals where the infection spread rapidly. A case in point is a medical professor who traveled to Hong Kong on 21 February and transmitted SARS-CoV to other residents, who further spread it to hospitalised patients in Hong Kong as well as other countries like Vietnam, Singapore and Canada. “Eventually, a total of 8096 patients were infected in over 30 countries among five continents and 774 (9.5%) of them died,” quotes a study in ScienceDirect.
Similarly, in South Korea in 2015, one MERS patient infected over 80 other patients, health care staff and visitors in three days.
The Lesson
Mapping these trajectories and patterns of transmission are crucial in order to know just how important maintaining social distance and following the necessary precautions is, and identifying loopholes where measures and policies need to be directed.
‘Social-spreaders’ may not be causing the damage intentionally, and thus must not be stigmatized. But knowing their possible existence is important because:
You can never know if you are a super-spreader.
Especially so if you are asymptomatic.
The solution is simple. Self-isolate, stay indoors and follow hand and respiratory hygiene. If you notice any symptoms, consult a doctor and get tested if advised. A single person’s complacency or carelessness can inadvertently affect several others, some of whom may succumb to the disease.
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