Snohomish County was state’s ground zero, analysis suggests

A genetics and infectious disease expert studied the DNA of individual cases to trace transmission.

Trevor Bedford (Fred Hutchinson Cancer Research Center)

Trevor Bedford (Fred Hutchinson Cancer Research Center)

SEATTLE — A genetics and infectious disease expert at Seattle’s Fred Hutchinson Cancer Research Center said Tuesday that additional analysis of the spread of the novel coronavirus, using genetic markers, has led to him conclude that as many as 570 Washington residents may have contracted the virus, many of them without knowing it, and have been spreading it through the community with Snohomish County as the outbreak’s center.

Trevor Bedford posted some of his initial findings on Twitter over the weekend, concluding that the genetic relationship between the first confirmed case of the disease — a Snohomish County man hospitalized in Everett in January — caused by the virus COVID-19 was so genetically similar to the second case reported on Feb. 23 that they almost certainly came from the same source.

Bedford said that the transmission likely began with an individual whose infection was missed because early guidelines limited testing to individuals who had traveled from China. He concluded, however, that the coronavirus, also known as SARS-CoV-2, was moving quietly through the community, a fact health officials acknowledged Monday as they declared a health emergency and announced six people have died from the disease in Washington.

On Monday, in a new string of tweets elaborating on his earlier observations, Bedford stated that the initial case in January — which he refers to as WA1 — likely “infected someone who was missed by surveillance due to mild symptoms and a transmission chain was initiated at this point in mid-Jan.”

Since then, Bedford believes, the virus has been moving through the community at a rate in which the number of cases doubled roughly every six days. Bedford concluded that rate of infection, taking into account a projected margin of error, would mean that there are as many as 570 infected individuals as of Sunday, and that number is growing. One of Bedford’s colleagues, using another method of tracking and projecting infections, came up with a more conservative estimate of 330 infections since roughly Jan. 15.

The first case reported in Snohomish County is the nexus from which Bedford said the virus will continue to spread, likely into more dense urban areas.

“We believe this particular transmission chain will have a foci in Snohomish County,” he wrote “We’re working as fast as possible to understand extent of spread in the greater Seattle area.”

Bedford said his recent analysis remains preliminary, and that he will refine his findings as more data becomes available.

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