Saturday, March 14, 2020

Inexplicable Covid-19 data, and a warning/ Nass

The scope of this epidemic does not fit all the data we have been given.

The Rzero number has to be greater than 2.2, much greater, to get so many cases so quickly in Wuhan and Lombardy, if the earliest case occurred in November-December, and the doubling time of the epidemic is 6 days.  The incubation period is said to be a median of 5 days.

And how is this for a statistic?  89 of 175 executives who attended a Biogen conference in Cambridge, MA came down with Covid-19.  That is half the people at the meeting!  I can't think of any other disease that spreads so widely.  While this reflects our lack of immunity, as a population, to the illness...well, it is still a phenomenal statistic. 

The rapid increase in cases does, however, fit existing data that showed cases had viable virus in nose or throat prior to developing symptoms, and after becoming clinically well.  In this small study, the MEDIAN period of contagiousness was 20 days.  Which is much longer than just about any other respiratory virus.  The longest period during which someone was potentially contagious was 37 days.  While patients developed antibodies (aka Seroconversion) after 6-12 days, this was not followed by a rapid decline of viral load, as expected.  Were scientists measuring the wrong antibodies, or do antibodies provide little benefit in this disease?  We should find out more about this as small experiments using convalescent serum in patients are ongoing.  

How long does the virus live on surfaces?  In indoor air?  Because the virus' viability decays in a logarithmic fashion, it is not either "viable or gone."  Instead, after a period of time (one half-life) half the virus is viable.  After another half life elapses, 1/4 of the virus is viable.  After another half life passes, 1/8 of the virus remains viable.  So there is no clear answer.  The answer depends on how many viral particles are on the surface to start with.  And it depends on how many viral particles are needed to cause an infection (which is termed the inoculum size). 

A German study of nine patients who had been in close contact to an index case, found 1,000 times as many viral particles per throat swab as SARS:  500 million (5 x 10 to the eighth power), occurring before the fifth day of illness.  Which is probably before patients realize they may actually have the Coronavirus.  It also suggests you merely need to breathe the same air as a patient to inhale enough virus to become infected.

Update 3/16/20:  WHO finally realizes the virus is airborne.

It would make sense that virus persists a long time on surfaces like glass, plexiglass and steel (days on average), and that relatively few viral particles are needed to cause infection.  And this virus can persist for hours in air (or maybe days, according to a NIOSH PP describing the the behavior of different sized particles in air. (see slide 12)

How could so many people in Lombardy become critically ill at the same time?  Two weeks ago Italy had no Covid deaths and a handful of cases.  Today Italy reports 1441 deaths, and 1518 seriously ill Covid patients.

This does not comport at all with an Rzero of 2.2, or even 10.  Some may blame the degree of spread on so-called superspreaders.  But if there are many superspreaders, then the Rzero needs to reflect them.

Something else to think about:  if both the Ohio governor and Ohio's top health official are correct and at least 1% of the population have already been infected, then we either have a less virulent mutation here in the US, or the vast majority of US cases are in the 0-14 day sweet spot of the infection, before things suddenly go south.  If my second hypothesis is correct, a disaster is looming.  I pray this infection is losing virulence as it mutates.

Lots of questions.  But one conclusion is clear:  social distancing is hugely important and should be taken very seriously by everyone.  And a lockdown, as has occurred in Italy and Spain, will only be effective if undertaken before there is widespread contagion.

While I am not generally a fan of Zeke Emanuel, this piece on Covid's spread and what is needed to slow it, is quite good.  


Anonymous said...

Dr. Nass,
Thank you for continuing to share your wisdom and knowledge on this subject and many more. I have the utmost respect for you and your work. We are very blessed to have you in our corner. With immense gratitude, ~Rebecca

Chevalier for Family Court said...

Thank you for refocusing our understanding. So much misinformation out there.