1/ This is what has been worrying epidemiologists about #COVID19- if asymptomatic/pre-symptomatic individuals are driving the outbreak, then coming out of lockdown will be exceedingly difficult
here's what it might take
science.sciencemag.org/content/early/…
here's what it might take
science.sciencemag.org/content/early/…
2/ I have to admit that I was confident that - like every other respiratory viral outbreak we'e dealt with- COVID outbreak was being driven by symptomatic people producing lots of virus and coughing it out.
Dr Fauci captures that confidence here (Jan 28)
Dr Fauci captures that confidence here (Jan 28)
3/ But there were worrisome indicators- like asymptomatic and pre-symptomatic people showing darned high levels of viral titres
here's a study from Washington State Nursing Home residents (A lower Ct value means a higher amount of viral RNA)
cdc.gov/mmwr/volumes/6…
here's a study from Washington State Nursing Home residents (A lower Ct value means a higher amount of viral RNA)
cdc.gov/mmwr/volumes/6…
4/ This is distinct from the question of how many people with infections don't have symptoms- it's how many of those people are INFECTIOUS, not just infected.
If there are lots of asymptomatic, non-infectious, that's a Good thing! (earlier herd immunity)
Infectious= Very Bad
If there are lots of asymptomatic, non-infectious, that's a Good thing! (earlier herd immunity)
Infectious= Very Bad
5/ The way we conquered SARS, and Ebola, was to diagnose people who are sick, and isolate them, cutting down on the spread to others
But if a lot of the infections were during those patients' pre-symptomatic phase, then many of infections have already occurred
More worrisome,
But if a lot of the infections were during those patients' pre-symptomatic phase, then many of infections have already occurred
More worrisome,
6/ This is an amazing twitter thread from @PeterKolchinsky about the virology of why COVID may be different from SARS in this respect (has to do with how it attaches to ACE2 receptors in throat)
7/ This also means that the virus is present in throat secretions, not just deep in the lung.
here's a great study that carefully measured samples from patients in the "Munich Cluster" who were exposed and followed when they had prodromal, very mild symptoms.
HT @dweglein_epi1
here's a great study that carefully measured samples from patients in the "Munich Cluster" who were exposed and followed when they had prodromal, very mild symptoms.
HT @dweglein_epi1
8/ From an epi point of view, to reduce the spread, have to get early-symptomatic tested sooner, test results sooner, self-isolating sooner (and a lot of focus on environmental droplets)
But there's another population to worry about- those who develop no symptoms
But there's another population to worry about- those who develop no symptoms
9/ If they are not symptomatic, why would they ever get tested? Do we have to literally test everyone, all the time?
That doesn't seem feasible.
As a result, most of your infections will be undocumented. (86% in China, they estimate)
That doesn't seem feasible.
As a result, most of your infections will be undocumented. (86% in China, they estimate)
10/ Another option, of course, is not to test everyone, but to isolate everyone. That's what we're doing, and it works!
That's why China was able to control the spread despite the estimated high number of potentially infectious and undocumented infections.
But how to get out?
That's why China was able to control the spread despite the estimated high number of potentially infectious and undocumented infections.
But how to get out?
11/ We need to be able to test and isolate a LOT more people early in the infection, with milder and prodromal symptoms
And we need to do aggressive contact tracing of those cases - quickly
Because we can "cheat up" + catch the contacts a few days before symptom onset- OR NO SX
And we need to do aggressive contact tracing of those cases - quickly
Because we can "cheat up" + catch the contacts a few days before symptom onset- OR NO SX
12/ That's how you test and isolate (or just quarantine) a significant number of people who would otherwise be infectious and pre-symptomatic/asymptomatic
The sample of contacts of known cases is enriched with them
That's @DrTomFrieden #BoxItIn strategy
The sample of contacts of known cases is enriched with them
That's @DrTomFrieden #BoxItIn strategy
13/ To be clear, having a lot of asymptomatic transmissions also reduces the effectiveness of contact tracing
So even with this #boxitin strategy, we need to continue pretty robust physical distancing as we slowly ease up on lockdown, AND MONITOR SUPER CLOSELY FOR RESURGENCE
So even with this #boxitin strategy, we need to continue pretty robust physical distancing as we slowly ease up on lockdown, AND MONITOR SUPER CLOSELY FOR RESURGENCE
14/ This is also why there might be an even greater role for "universal precautions" in healthcare - getting enough personal protective equipment that every HCW can get a mask a day, and use it for every patient interaction, regardless of symptoms
(and public mask-wearing too)
(and public mask-wearing too)
15/ It also means that primary care practices are going to be in the frontlines of this outbreak response. They have to have the PPE and access to tests to be able to diagnose COVID quickly...and we have to make sure that they are not shuttered-many are in deep financial distress
