Infection = Exposure X Time. What other ways can you be exposed?

Infection = Exposure X Time

Yesterday we talked about how being in an enclosed space like in a cinema or plane increases the risk of infection because of the extended time spent together.

If you accept the following Business Insider stories about transmission in an enclosed space, you should think many times before going to such a place.

• The odds of an infected person spreading Covid 19 in a closed environment is 18.7 times greater compared to an open-air environment (OK, this has not been peer-reviewed)

• In 318 cases in China involving 3 or more people, only one case involved people outdoor

But let's move from “Time” to “Exposure”

When you think about exposure, you have to think not of just being 1 or 2 meters apart.  As an article in VOX  suggested, you have to think of other dimensions too. 

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Exposure is more than just about physical distance. The type of activity and the environment are equally important.

When it comes to the environment, we know that enclosed space is riskier than in an open space.  

Along the same lines, an air-conditioned room is riskier as the air gets re-circulated.  Unless of course, you are in a special air-conditioned space where the air is filtered/treated before it is re-circulated.

I am not sure whether how many saw the video of the US army general explaining to Governor Cuomo what had to be done when setting up the field hospital in one of the stadiums in New York -  they had to set up their own air-conditioning system to “clean” the re-circulated air.

In this context, it is safe to fly?   According to my Google search: 

“The air you're breathing inflight is re-circulated and filtered regularly, which means you're not being exposed to things like bacteria and viruses through the recycled air.

In fact, because of the high-efficiency filters on most commercial airlines and the frequency the air is re-circulated and filtered, the air you're breathing on your flight is likely much cleaner and less contaminated than most office buildings and is on par with the air in most hospitals.”

Wow.  We are safe from getting infected from re-circulated air while being in a plane.  

But there is still a risk - it comes from breathing in the virus before the air is re-circulated.  Ha. You cannot win.

Since we are on the subject of air-conditioning, 

• Is your office air-conditioning system of the same standard as the airplane?
• Shouldn't all the public gathering places eg cinema, convention hall check that their air-conditioning system can filter/treat re-circulated air as part of the SOP?

I am sure you can think of other environments where the risk of infection is higher. 

When it comes to activity, the risk is because Covid 19 is spread from respiratory droplets. The risk of catching the coronavirus “is breathing in other people's breath.”

 

When it is put like that then those activities that involve lots of people with heaving breathing, lots of talking and shouting, laughing, or singing are riskier eg an air-conditioned gym with lots of people exercising with droplets flying all over the place.  

VOX cited a Washington state case where a person with the virus attended choir practice, and more than half of the other singers subsequently got sick. This was labeled a “super-spreading” event, as one infection led to 32 others. 

But what made this event so risky was the convergence of many risk factors: 

• the singing activity during which the infected person released viral particles into the air, 

• the time spent together - the practice was 2.5 hours,

• the interaction between the choir members in an enclosed space - not only did they all practice together, but they also split up into smaller groups and shared cookies and tea.

So now I understand why karaoke, clubs, and bars are associated with Covid 19.  There is much singing, shouting, cheering and close conversations (due to the noise)

Moral of the story. Spend time in the library!

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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.