Survival Odds – An Optimistic View


As it turns out my dentist and close friend, Dr. David Bergen, is also a bit of a mathematician/ponderer (who else would have spent the first month of the shut down taking a calculus course for fun!?!).

Lately, we had some very interesting discussions about his calculations of the risk of him catching COVID at the office, and presumably his patients’ risk of catching COVID at his office – which naturally will be much less than his own. I asked him if he would put his thoughts on paper so that I could share these enlightening calculations with you all – to which he has agreed.

I think all of the following information takes on added weight as we head into a “Second Wave” where the biggest concern for dentists will likely be patient hesitancy.  The following should not only be comforting to dentists but also to patients. Here are the odds, as best said in Dr. David Bergen’s words, exactly as he gave them to me:

I am a dentist.  A big part of what I do involves the creation of aerosols.  Aerosols and droplets appear to be how COVID is transmitted in the vast majority of cases.  So, one day, I got to wondering: what is my actual risk?  Do I have some sort of a death wish?  I thought that I should figure this out.  Some assumptions and approximations were made, but I think that mostly I erred on the pessimistic side.  However, it is easy enough to redo the calculations with numbers derived by different perspectives.

When I started thinking about this it was spring and about 3 cases of COVID were being diagnosed in the Niagara Region every day.  From my reading it seems that for each diagnosed case there was probably one asymptomatic or undiagnosed case: so likely another 3 people were out there not knowing that they had COVID.

We do excellent screening and people are reasonable, so it was extremely unlikely that one of the active cases would attempt to see us while their infection was still active and transmissible.

It appears, again from my reading, that if one gets COVID, the time period in which you can transmit the virus is about 14 days.  If 3 people were becoming infected and didn’t know it, and remained infectious for 14 days, likely there were 42 people in the Niagara Region with infections, but undiagnosed and unsuspected of COVID at any point in time. 

In Niagara, we have (conveniently) 420,000 residents, so if 42 of them had unsuspected COVID at a given moment in time, that would be one person in 10,000.

 In our very small (one chair) dental office, we average around 10 people a day: some days more, some far fewer.  We work 5 days a week.  At the end of the year, we will have had about 2,500 patient visits.

If one person in 10,000 has undiagnosed and unsuspected asymptomatic COVID, we will, on average encounter one such person every 4 years.

 So, if I work 5 days a week, my chances of encountering someone with COVID was (in the spring) once every 4 years.

 If my PPE (facemask, etc.) are 99% effective, I would then have one chance in 100 of becoming infected (COVID is indeed infectious).  So, 1 in 4 years multiplied by 1 in 100 occurrences means that I would have to work for 400 years to catch COVID once (on average).

I’m in 71, but in good health, and so assume my risk of something life-altering (death or incapacitation) occurring is, to the best of reading and understanding, probably 1 in 20.

 1 in 400 multiplied by 1 in 20 gives me 1 in 8,000. 

According to these calculations, I would have to work for 8,000 years to catch a terminal or disabling case of COVID from working in my dental practice.

Another way to look at this is that if I had been practicing dentistry continuously since just after the last ice sheet retreated from our part of the world, I would have had a catastrophic run-in with about COVID once.  I would have had many other things happen and have died many times over from other causes, but from COVID: probably just once.

Interestingly, our odds of dying in a motor vehicle accident are about 1 in 8,300: about the same odds as my estimated COVID risk.  They are both terrible ways to go, but neither is currently waking me up at four in the morning with feelings of anxiety.

In late August we were down to 1/2 new case every day, so at that point, I would have had to work for 48,000 years.  However, the second wave is breaking, so the odds keep changing.

The overall thing is that, unless things get really, really bad, I have other things that I choose to worry about.

Now it is important to keep in mind that while David Bergen has a very busy, unique one operatory, a virtually by-invitation-only practice overlooking Lake Ontario.  If you work in a larger office, somewhere other than the Niagara Peninsula, you may need to modify the numbers somewhat.

The bottom line however is that for dentists, staff, and patients going to the dentist’s office, it is likely much safer than going grocery shopping.  David also happens to be my dentist and I am honoured to be sharing my blog space with him.