[Taxacom] Coronavirus spread speed

Richard Zander Richard.Zander at mobot.org
Mon Mar 16 08:47:41 CDT 2020


I think Ken Kinman is being reassuring. Yes, exponential curves level off eventually as available unvirused people decrease and social distancing and isolation help curb spread of disease. The bottle is half full.

To those suffering the exponential rise of contagion, however, the bottle is definitely half empty. 

Exponential means some value increases by a power. A population of 2 rabbits becomes 4 rabbits, as 2^2 works out. Doubling 5 times is 2^5 or 32 rabbits. 

But the rate of virus contagion is, I think, a second order Markov chain. 2 rabbits each create 2 more rabbits, giving 4 rabbits plus the first 2 rabbit or a total of 6 rabbits.

I understand that coronavirus has a contagion rate of 2.4. Each case creates 2.4 new cases. One step of contagion yields 3.4 cases. At any point, the number of cases in total creates 2.4 more cases per sick person. This is the equivalent, I think, to 3.4^n, where n is the number of rounds of contagion. Ten rounds, or 3.4^10, leaves 206,438 cases. Fifteen rounds of contagion leaves 94, 795, 878 cases. This assumes this increase is on the steep rise, bottle half empty, portion of the S curve.

The Governor of Washington State is actually not scaring people enough, he is substituting a simple exponential explanation for the really scary reality.

Richard Zander


-----Original Message-----
From: Taxacom [mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Kenneth Kinman via Taxacom
Sent: Sunday, March 15, 2020 3:45 PM
To: Taxacom(taxacom at mailman.nhm.ku.edu} <taxacom at mailman.nhm.ku.edu>
Subject: Re: [Taxacom] Coronavirus spread speed

Hi all,
      This past week the Governor of Washington State used exponential growth to scare people.  Quotes: “If we assume there are 1,000 or more people who have the virus today, what the experts are telling us, in an epidemic like this, looking at the characteristics of this virus, people who are infected will double anywhere from five to eight days,” he said. “If you do that math, it gets very disturbing.” “When something doubles every day, it gets to a very large number very quickly. If there are 1,000 people infected today, in seven or eight weeks, there could be 64,000 people infected in the state of Washington,” he said.   And that by the end of May it would presumably have infected 250,000.  [Note:  I think he meant to say "doubles every week", not every day ].
      But he presumably failed to mention that the number of cases in China had dropped dramatically.  During the first half of March, China only went from about 80,000 cases to 81,000 cases (far from being exponential).  If warmer wetter weather does decrease the spread of the coronavirus, such dramatic flattening of the curve might happen even sooner in most countries.  All the "chicken little" pundits will then have to find something else to up the media's television ratings, and the sales of toilet paper will then plunge for several months since people had bought so much of it.
                                           ---------------Ken
P.S.  Although France has decided to intensify its nationwide shutdown, it also decided not to postpone today's nationwide elections.  Very mixed messages on the same weekend.  But I would really hate to be one of those passengers returning from Europe to the U.S. this weekend, packed together like sardines waiting to be screened.  If there are infected people among them, they could spread that (or any other) virus very quickly.   Airplanes have been compared to petri dishes and cruise ships compared to giant petri dishes.   And the airport terminal at Chicago looked awful:
    https://www.instagram.com/p/B9we3vjHzDJ/?utm_source=ig_embed


________________________________
From: Taxacom <taxacom-bounces at mailman.nhm.ku.edu> on behalf of Richard Zander via Taxacom <taxacom at mailman.nhm.ku.edu>
Sent: Sunday, March 15, 2020 1:12 PM
To: Taxacom(taxacom at mailman.nhm.ku.edu} <taxacom at mailman.nhm.ku.edu>
Subject: [Taxacom] Coronavirus spread speed

I just read a pundit item on the Web that said the novel coronavirus spread was exponential. The writer submitted the analogy of a pond with pond-lily spreading exponentially. At first you hardly notice the spread but then it speeds up until when the pond is half covered with pond-lilies, then the next step is complete coverage to reflect doubling.

I think this scenario is wrong and dangerously complacent.

Coronavirus spreads, it is said, at the rate of 2.4 new cases per old case. Assume the old cases survive and are infective. Thus, 1000 cases creates 2400 new cases plus the old cases, and we get 3400 cases. 100,000 cases will generate a total of 340.000 cases in the next step, assuming sparse distributi9on and no fast recovery. So, in the case of an analogy with a lily pond, after the pond gets covered only one-third of the way with pond lilies, then the next step is full coverage.

It may well be that rapid spread of the coronavirus will go on faster than recovery and loss of infectiveness of old cases (two weeks?).

If this is right, old taxonomists should retire to a fortress and hole up until the tsunami passes. It will be like a wall falling on you.

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