The coronavirus has been circulating undetected and has possibly infected scores of people over the past six weeks in Washington state, according to a new report.
The researchers conducted genetic sequencing of two virus samples.
Trevor Bedford, a computational biologist at Fred Hutchinson Cancer Research Center in Seattle, said two samples were almost identical genetically from two patients.
One patient traveled to China in mid-January and was the first person diagnosed with the disease in the United States.
The other patient who was recently diagnosed in the same county is a high school student with no travel-related or other known exposure to the coronavirus.
“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.”
Officials in Seattle and King County on Sunday announced that two more people have tested positive for the coronavirus.
Both patients are men in their 60s and are in critical condition.
This totals eight cases in Washington state, six of them in the same county.
Health officials in Washington state and across the nation said they expect numbers will continue to rise in the wake of the decision by the U.S. Centers for Disease Control and Prevention last week to widen testing guidelines. Over the weekend, new cases were reported in Americans who had recently traveled to South Korea and Italy, including one person in Rhode Island, the state’s first case.
The health department in Santa Clara County, California, in the heart of Silicon Valley, announced three new coronavirus cases Sunday evening, bringing to seven the total number of cases there. The announcement gave few details about the cases.
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California and Oregon, like Washington, have reported coronavirus infections in people who did not travel to regions hit hard by the outbreak or have contact with people known to be infected. The United States has dozens of other confirmed infections, the majority of them people who were among the passengers on the cruise ship Diamond Princess.
The international picture has continued to worsen, with spikes in cases in South Korea, Iran and Italy in recent days. Worldwide, almost 90,000 people have been infected with the coronavirus, and 3,000 have died.
The research reported by Bedford is preliminary, and further analysis could alter the conclusion. 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.
The CDC has been in touch with Bedford, and although agency experts note that his hypothesis has validity, scientists need more data, according to a Department of Health and Human Services official, who spoke on the condition of anonymity to talk candidly. “It is far from definitive,” the 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.