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Study suggests Placer County saw three times more COVID-19 cases

A Stanford University study suggests the COVID-19 infection rate in Placer County was 3 times higher in March than what was previously confirmed

PLACER COUNTY, Calif. — A group of Stanford University researchers spent five months looking over COVID-19 cases in Placer County. Their findings suggest a significant difference between the number of positive cases the county’s health department reported, and the number of residents who had antibodies.

Stanford conducted this study with 2,000 participants between October 2020 and March 2021.

On March 1, Placer County Public Health reported 19,861 cases of COVID-19. In March, Stanford University researchers found 12.5% seropositivity. Seropositivity is the number of participants in the study who were found to have antibodies in their system. 

When you compare that percentage with the 400,000 people living in Placer County. It shows 49,791 cases for the month of March.

Stanford University’s Julie Parsonnet said the test isn’t perfect. It does account for error. With that in mind, the researchers determined the county should have seen 62,139 cases in the month of March.

This means 68% of cases went unreported. UC Davis Health Dr. Dean Blumberg explained how this could happen.

“We know not everybody with COVID, for example, not everybody is diagnosed with it and then reports it. Not everybody is going to be tested and some people might have asymptomatic infection.”

Parsonnet said this isn’t something the county needs to worry about. The percentage of unreported cases is right on track with the national level for that time frame.

“I think Placer County, all in all, looks a little better than other places that have done similar studies,” she said.

Historically, vaccines wiped out other diseases and Parsonnet said any county should focus on getting vaccines out.

“This study indicates that that’s really the right way to go, to push everybody to get vaccinated,” Parsonnet said.

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