Stanford tracks early spread of Covid-19 in Bay Area by testing pooled samples

So for most of those who felt they already had the SARS-COV-2 in Jan or Feb it is very unlikely to be true.

To quote:

Prior to launching the clinical test, Pinsky and his colleagues tested samples collected from the back of the throat or lung airways of 2,888 people who sought care at Stanford Health Care between Jan. 1 and Feb. 26 for respiratory symptoms but who had tested negative for common respiratory viruses. They combined the samples in groups of nine or 10, then tested the pooled samples for the presence of SARS-CoV-2.

Of the 292 groups of pooled samples, only two were positive. Further analysis showed that two people, one in each positive group, were infected with SARS-CoV-2.

“I was a little surprised the prevalence was so low, but it was consistent with what our public health officials in California were observing through normal surveillance methods,” Pinsky said. “Our positives came about the same time that they were identifying an uptick in COVID-19 diagnoses.” The Bay Area’s first COVID-19 diagnosis was made in early February.