“An already substantial outbreak in Washington State”

Report from Trevor Bedford, scientist at the Fred Hutchinson Cancer Research Center in Seattle (emphasis mine):

Trevor Bedford
@trvrb
·
1h
Replying to
@trvrb
and
@seattleflustudy
This case, WA2, is on a branch in the evolutionary tree that descends directly from WA1, the first reported case in the USA sampled Jan 19, also from Snohomish County, viewable here: https://nextstrain.org/ncov?f_division=Washington
2/9
Image
Trevor Bedford
@trvrb
·
1h
This strongly suggests that there has been cryptic transmission in Washington State for the past 6 weeks. 3/9
Trevor Bedford
@trvrb
·
1h
It’s possible that this genetic similarity is a coincidence and these are separate introductions. However, I believe this is highly unlikely. The WA1 case had a variant at site 18060. This variant is only present in 2/59 viruses from China. 4/9
Image
Trevor Bedford
@trvrb
·
1h
I’d assess the p-value for this coincidence at 2/59=0.03 and so is statistically significant. Additionally, these two cases are geographically proximal, both residing in Snohomish County. 5/9
Trevor Bedford
@trvrb
·
1h
I believe we’re facing an already substantial outbreak in Washington State that was not detected until now due to narrow case definition requiring direct travel to China. 6/9
Trevor Bedford
@trvrb
·
1h
We will be working closely with @KCPubHealth
and @WADeptHealth
to investigate the full extent of the outbreak. 7/9
Trevor Bedford
@trvrb
·
1h
We’re hoping to update soon with better estimates of the number of infections in Washington State using available data. 8/9
Trevor Bedford
@trvrb
·
1h
Thank you to the @seattleflustudy
team, and particularly to @lea_starita
, for exceptionally fast turnaround from diagnostic assay at @WADeptHealth
to sequenced genome. 9/9
Trevor Bedford
@trvrb
·
1h
An update, because I see people overly speculating on total outbreak size. Our best current expectation is a few hundred current infections. Expect more analyses tomorrow.

Things are not looking great for the West Coast at this point. On a side note, this tends to suggest that my proposal of January 23, to “shut down international travel until we get this thing firmly under control,” was actually too late.

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