The start of the covid-19 pandemic in the U.S. may have been earlier and far larger than official records indicate, according to a new study. Researchers found that a substantial portion of people, including children, in Seattle who were suspected of having the flu this past winter likely had covid-19 instead. It also estimates the city may have had thousands of cases by early March, when barely over a hundred cases in the state were reported.
Researchers at the University of Texas at Austin looked back to two different periods during the earliest days of the pandemic: the month of January in Wuhan, China, and the weeks of late February and early March in Seattle, Washington. They studied data from hospitals and doctors’ offices that had collected throat swab samples from outpatients diagnosed with flu-like symptoms; these samples were later reanalyzed for the presence of the coronavirus that causes covid-19.
In both cities, most of these cases turned out to be flu, but over a third were actually covid-19 in Wuhan, while more than one in every 10 cases were covid-19 in Seattle, the team concluded. Based on the known trajectory of the flu season in both areas, the researchers then created a model of how early and widespread covid-19 had likely been during these first weeks.
By their estimates, Seattle already had at least 9,000 cases by March 9, when the city implemented lockdown measures such as closing schools and there were fewer than 200 cases reported in the state as a whole; of these, thousands likely involved children. Wuhan similarly had over 12,000 cases by January 22, right as the Chinese government issued its lockdown and had only a little over 400 official cases. They also estimated that people were spreading the virus in Seattle by the first week of January and possibly even as early as Christmas, while the first Wuhan case emerged sometime between late October to early December.
The study’s findings were published in the journal EClinicalMedicine.
Other studies have similarly placed the start of the pandemic further back in time than official records have shown (the first detected case in the U.S., in Washington, was January 15). But this study not only dates the origins of the outbreak in the U.S. further back than January 15—it also suggests this spread was far more extensive in the first hotspots than we had known. And the researchers’ method of comparing flu to covid-19 cases this past winter could also be used to estimate how many covid-19 cases were mistaken for flu in other areas in the U.S. hit early by the pandemic, such as New York City and California.
“We can go back and piece together the history of this pandemic using a combination of investigative techniques and modeling,” said lead author Lauren Ancel Meyers, a professor of integrative biology and statistics and data sciences at UT Austin, in a statement released by the university. “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 has its limitations. The model’s estimates are based on a number of assumptions, such as how many people can carry the virus without becoming sick (asymptomatic patients). If 50 percent of all cases are asymptomatic, as some research has found, then the team’s numbers would actually undercount the extent of covid-19’s spread in Seattle and Wuhan.
But coupled with other research, this study is only the latest to show how truly unprepared the U.S. really was for the pandemic—a problem that persists more than six months later.