In early March, the state of Washington had reported just over 100 coronavirus cases. But Seattle alone may have actually had thousands of infections at that point, according to a new study, because so many illnesses were thought to be the flu instead. The findings by researchers at the University of Texas at Austin mean COVID-19 might have begun spreading sooner—as early as late December in Seattle—and infected far more people in the US than official counts show, Gizmodo reports. "We can go back and piece together the history of this pandemic using a combination of investigative techniques and modeling,” said the study's lead author. "This helps us understand how the pandemic spread so quickly around the globe and provides insight into what we may see in the coming weeks and months."
The study looked at data from doctors and hospitals that took throat swabs from outpatients with flu-like symptoms—for January in Wuhan, China, and for late February and the first of March in Seattle. The samples had been checked again later to look for the coronavirus. The team found that more than one-third of Wuhan's patients actually had the coronavirus, and more than 10% of Seattle's had it. That led to the estimate that by March 9, when not 200 coronavirus cases had been reported in Washington, Seattle already had at least 9,000, probably thousands of them children. "Even before we realized that COVID-19 was spreading, the data imply that there was at least one case of COVID-19 for every two cases of flu," the author said in a release. All of the model's assumptions may not hold up, but other researchers have reported similar findings. "We could reasonably determine the prevalence of COVID-19," the author said. (Read more coronavirus stories.)