Thread by @sinanaral

[The Silent Secret of COVID-19] One dimension of the novel coronavirus that is critical to containment but has not received enough attention is the prevalence of asymptotic cases in the population. 1/

If a large fraction of positive cases are 'hidden,' they could escape public health interventions and prevent the effectiveness of social distancing. What do we know and what does it mean for our fight against the virus? 2/

When passengers of the quarantined Diamond Princess cruise ship were tested, 621 of 3,011 people tested positive for COVID-19 (21%) and 322 of the 621 positive cases showed no symptoms of the virus (52%). mhlw.go.jp/stf/newpage_09… 3/

A paper in Science, modeling data on reported infection in China found 86% of all infections were undocumented & the transmission rate of undocumented infections was 55% of documented infections, though undocumented carriers were much more numerous. science.sciencemag.org/content/sci/ea… 4/

When the entire town of Vo Euganeo in northern Italy was tested in an experimental attempt at comprehensive surveillance in a small town, 3% of the population was infected but "most [positive cases]... had no symptoms of the flu-like disease at all." independent.co.uk/news/world/eur… 5/

The rates of asymptomatic prevalence, which seems to be approximately 65-70% or at least between 52% and 86%, has two important implications for containment efforts... 6/

First, it is *extremely* important that *everyone* consistently practice social distancing and isolation during all non-essential activities. The vast majority of people carrying COVID-19 don't know they have it and show no signs or symptoms. 7/

Second, we must not only ramp up essential testing, beginning with testing of healthcare workers & symptomatic cases on the front lines, but we must also rapidly accelerate our broader surveillance effort to test large fractions of people who show no signs of having the virus. 8/

Broad surveillance could be achieved by using less precise but faster and cheaper antibody blood tests. While, clinical, RNA-based, diagnostic tests could be used on the frontlines to confirm likely cases. 9/

Antibody blood tests look for antibodies developed to fight the virus in the blood of the infected & can tell if a person has been infected even after they have recovered because the body retains antibodies against pathogens it has already overcome. sciencemag.org/news/2020/03/n… 10/

Current clinical testing is biased toward the sick & ill. So we don't know how much COVID-19 there is or how dangerous it is. This uncertainty => over and/or under reaction. 11/

Broader surveillance testing should use (stratified) random sampling & active learning to help us learn where the virus is quickly. statnews.com/2020/03/17/a-f… 12/

India has already begun to implement random sampling of people who display flu-like symptoms but don’t have any history of travel to outbreak zones 13/ economictimes.indiatimes.com/news/politics-…

While a large scale stratified random sample may be costly & impractical, in Holland they are taking 10,000 samples from all blood donations in the past week (shared by @PeterLugtig)
nos.nl/artikel/232758… 14/

You could also imagine beginning with a few small representative cities across the US, as several people including @cdsamii have suggested. 15/

But the current approach, no matter how large, will always provide biased estimates of prevalence & morbidity/mortality because, as @deaneckles pointed out, computing standard confidence intervals from big, biased data does not yield valid inference. statistics.fas.harvard.edu/files/statisti… 16/

i just saw this... asymptomatic, not asymptotic (my auto correct is well trained)

Also... There are some reports that CA has been doing random testing and that this surveillance informed their policy:

https://twitter.com/yashar/status/1241525616219787264?s=19

CA is using testing as "community surveillance"... "broad random tests of otherwise young, healthy people, which allowed health officials to improve their use of scarce medical resources."

m.arcamax.com/currentnews/ne…