A new study has changed the thinking on how the first big outbreak of COVID-19 in the US got started, reports STAT News. And the finding has implications for how states try to stem the spread of the virus. Until now, health officials were pretty sure that Washington state's outbreak could be traced to a man who returned from Wuhan, China, on Jan. 15 and tested positive within a week. They isolated him and tested people he came into contact with, and no new infections arose, at least initially. The state's second confirmed cased turned up on Feb. 28, this time of a person who had not traveled outside the country. Because the two strains of the coronavirus were similar, health officials concluded that the first patient, dubbed WA1, must have been the source of the second case. They figured the disease was silently spreading for six weeks around Seattle.
The new study, which has not yet been peer-reviewed, refutes that. “In all likelihood this didn’t start with WA1,” says Michael Worobey, lead author. “It started with some unidentified person who arrived in Washington state at some later point. And we don’t know from where.” This unidentified person probably returned to the US with COVID in mid-February, roughly a month after WA1 did. The Seattle Times lays out the implications: If WA1 was indeed the start of the outbreak, the idea of stemming the spread of the disease seems "hopeless." After all, health officials did everything right in terms of testing and tracing, and the disease still spread six weeks later. But if the second, unidentified person is the source—and the virus was circulating only two weeks or so before the outbreak began—that suggests widespread testing and tracing can work. (Read more coronavirus stories.)