Post #557: Vienna Metro parking lot, Tuesday 3/17/2020

Posted on March 17, 2020

Maybe we’re smarter than I generally give us credit for.

But if the scene above is typical, why are reported US COVID-19 cases still rising at an accelerating rate?

At this point, if this social distancing really has broken the chain of transmission, it’s just a matter of arithmetic to get from there, to a decline in the number of new cases reported daily.

Based on what I’ve read, the typical lag between infection and symptoms is 5-6 days.  The typical lag between onset of symptoms and testing is another 4 days.

So, the last cohort of people who got infected from public contact, before we got serious about this, will show up in the reported case counts … eh, on average, about 10 days after we got serious.  And once they show up, then the growth in case counts will begin to decelerate.

Of course, we didn’t get serious about “social distancing” all at once.  So there’s not like there’s one fixed date.  But if I had to pick a date, I’d say “last Friday”.  Or thereabouts.

But there will be additional new infections after the get-serious date that take place within what the Chinese termed family clusters.  I.e., even if we’re not transmitting the infection in public places, there will still be transmission within the home.  And so, if we follow the pattern observed in China, at some point, the new cases will shift from being a bunch of unrelated strangers to what amount to “add-on” cases within families.  E.g., a parent who picked something up at work just before we got serious about social distancing might pass that on to another family member some days after our “get serious” date.

And so what ought to happen, at this point , is that case counts will continue to rise alarmingly for something in excess of 10 days.  Somewhere around the 10 day point, the bulk of new cases will switch from being unrelated, to being within-family/family-friend infections.  And then at some point, when the family members of every infected person have developed symptoms and been tested, then the daily increase in case counts will decline.

Anyway, that’s the near-term game plan, as I understand it.  In a perfect world, we’d hit the inflection point — the new cases diagnosed daily would start to drop — eh, March 25th-ish.  A little over 10 days from when we got serious.  And at that point, the mix of new cases will shift to being intra-family infections.  Total cases will still go up, but the growth will fall off.

It took the Chinese about 25 days, after the point where they hit 400 total case, to hit that inflection point (See Post #550).  If we follow that same pattern, then we’d hit our inflection point around March 30-ish, or just shy of two weeks from now.

So, best guess, we’re still somewhere between one and two weeks away from that inflection point — the point at which the growth in newly-diagnosed cases slows.  That’s assuming every takes the social-distancing thing seriously.  And judging by Metro today, that looks like a pretty good assumption.