Thread by @trvrb

A follow up to Saturday's analysis of undetected #COVID19 transmission in Washington State.

https://twitter.com/trvrb/status/1233970271318503426

1/11

As before, the genomic data support a linkage between the case WA1 from Jan 19 and the case WA2 from Feb 24, both from Snohomish County. 2/11

This suggests that the case WA1 infected someone who was missed by surveillance due to mild symptoms and a transmission chain was initiated at this point in mid-Jan. 3/11

Because the case definition from mid-Jan until Feb 27 required direct travel from China, any of these subsequent cases in the transmission chain would not have been tested for #SARSCoV2. 4/11

Assuming an introduction into Snohomish County on Jan 15, Mike Famulare @IDMOD_ORG simulated onward transmission using consensus epidemiological parameters curated by the @MIDAS_Network (github.com/midas-network/…). 5/11

Running these simulations forward with a mean doubling time of 6.1 days, we estimate the number of current infections in this transmission chain on March 1 to be 570 with an 90% uncertainty interval of between 80 and 1500. 6/11

In addition to this "bottom-up" approach, Mike used a "top-down" approach in which we accounted for the single positive screening result out of the number of samples screened to date along with census information. 7/11

This approach leads to a similar estimate of the number of current infections at 330 with a 90% uncertainty interval of between 20 and 1500 infections. 8/11

We believe this particular transmission chain will have a foci in Snohomish County. We're working as fast as possible to understand extent of spread in the greater Seattle area. 9/11

Please consider this to be a preliminary analysis. We are actively working on this and will continue to update our numbers. 10/11

We are hugely thankful to @SnoHD, @KCPubHealth and @WADeptHealth for their support and clear thinking for state and local public health. They are doing a fantastic job. 11/11