Beware of the Super-Spreader

I across an article in the New York Times which stated that 20% of Covid 19 cases accounted for 80% of transmissions.  In other words, the bulk of the transmission is by “super-spreaders”.

This is something strange because most epidemiological models have the parameter called R0 which is how many people on average are infected by a sick person.  R0 is generally taken to be between 2 and 3 ie one sick person on average spreads the virus to 2 to 3 persons.

 

Do you remember our MOH stating we have brought down our R0 from 3.55 at the start of the MCO (refer to 14 May posting) to below 1?

So a super-spreader is one person with R0 way above the model range ie a “black swan” number. 

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How big is this number?

• Do you remember that when Covid 19 was in the initial outbreak in the UK, there was this story about a British national who infected at least 11 others – from his time in a ski resort to his home town before he was diagnosed with Covid 19. 

• The New York Times found that of the 349 local cases in Hong Kong, 196 were linked to just six super-spreading events. One person alone appears to have infected 73 individuals after frequenting several bars in late March. Weddings, temples, hot-pot dinners, work parties, and karaoke venues featured in the other super-spreader clusters.

There are other stories from other parts of the world of this super-spreader infection “power”

• 63 people in a Washington choir got sick after a group practice with an infected choir member

• When the virus first appeared in South Korea, 40 people were infected by one person who attended the same church service.

Actually, I am quite surprised that people have suddenly taken notice of these super-spreaders.

This is because we also have our super-spreaders (source Malaysiakini)

• Case 26.  The one index case spread to 25 others

• Wedding cluster:  One index case spread to 30 people

• Church cluster.  One index case infected one other person.  Then there were 22 second-generation cases although it is not clear whether all the 22 were infected by the lone 1st generation case.

Note that I have excluded the Tabligh and Tahfiz clusters as I think there were several index cases in each of these clusters. But more importantly, the Tabligh and Tafhfiz numbers are largely due to the multi-generation spread. (24 May posting) rather than super-spreading. 

Despite these super-spreader cases, there is a dispute about whether this is real.  Oh, the clusters are real.  It is the cause of the cluster that is disputed. 

The World Health Organization says it does not use “super-spreading” as a technical term. It adds, however, that “there can be incidents of transmission where a large number of people can become infected from a common source.”

“Super-spreader” can refer to either a person or the nature of an event. The spread of the new coronavirus depends on a range of environmental and epidemiological factors that ultimately lead to transmission in individual cases or clusters. 

These include the patient and what stage of the disease they are in, their behavior, their environment, and the amount of time spent in that environment.

What the dispute shows is that there is so much about the virus that we have yet to understand. So it is dangerous/foolhardy for any officials to pursue one set of measures based on a particular theory. 

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So to come back to the super-spreader story. 

 

Most super-spreader events are similar: The infected person attends an indoor gathering with lots of people, like a religious service, choir practice, or birthday party.

“The commonalities of these events inform health officials about the types of gatherings with the highest chances of facilitating the virus' spread.”

What it means is that if we avoid crowds, crowded places and close contacts, we can help to prevent the super-spreading event. 

At the same time, authorities should focus on rapid contact tracing and isolation together with social distancing to prevent the super-spreading.

Too bad.  WHO is not saying that we have some super-person with some special “powers” to spread the virus. Otherwise, it would be a simple case of isolating the super-spreaders quickly to control the spread. 

Unfortunately, It is all back to the old grind of 3Cs and 3Ws.  

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PS: This blog is for me to better understand COVID 19 as this will impact my investments. If you are also into equities, follow me at i4value.asia.

Disclaimer:  I am not an epidemiologist, healthcare worker, pharmacist, or staff in the Ministry of Health, but rather is someone with a strong interest in numerical analysis.  The content is an attempt to understand what is happening in the battle against COVID 19 from a data-based perspective. The opinions expressed here are based on information extracted from readily available public sources but I do not warrant its completeness or accuracy and should not be relied on as such.