The coronavirus has been circulating undetected and has possibly infected scores of people over the past six weeks in Washington state..."

"... according to a genetic analysis of virus samples that has sobering implications for the entire country amid heightening anxiety about the likely spread of the disease. The researchers conducted genetic sequencing of two virus samples. One is from a patient who traveled from China to Snohomish County in mid-January and was the first person diagnosed with the disease in the United States. The other came from a recently diagnosed patient in the same county, a high school student with no travel-related or other known exposure to the coronavirus. The two samples look almost identical genetically, said Trevor Bedford, a computational biologist at Fred Hutchinson Cancer Research Center in Seattle who announced the results of the research on Twitter late Saturday night. 'This strongly suggests that there has been cryptic transmission in Washington State for the past 6 weeks,' Bedford wrote. '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.'... Bedford said it is possible but very unlikely that the genetic similarity of the two virus samples could be a coincidence and reflect two distinct introductions of the virus into Snohomish County by infected travelers, rather than sustained person-to-person spread within the community.... 'It is far from definitive,' [a CDC] official said. 'The particular strain found in these two samples is widespread in China and elsewhere. It’s possible that someone else introduced the virus into the community 'that we didn’t pick up,' the official said. But this research could be evidence that the highly contagious virus has eluded efforts to contain it through travel bans, quarantines and other interventions. The virus may have been spreading in parts of Washington state among people who didn’t realize they were infected by it — they may have thought they had a cold or the flu."

WaPo reports.