https://news.usc.edu/170565/covid-19-antibody-study-coronavirus-infections-los-angeles-county/
Coronavirus infections more widespread than expected in L.A. County
A newly published, USC-led study has confirmed that, though many more L.A. County residents had COVID-19 antibodies than previously thought, most people have not been infected.
The researchers estimate that approximately 4.65% of the county’s adult population has contracted the new coronavirus.As with all statistical estimates, there is a range of uncertainty or margin of error. The analysis suggests that the fraction of adults in Los Angeles who contracted the novel coronavirus could range from as low as 
2.5% to just over 7%. The results verify 
preliminary results that had been released last month.Sood pointed out two important caveats: One, the results may have been skewed by an
 overrepresentation of people who experienced COVID-like symptoms in the past, potentially driving the number of positive tests up. Second, Sood emphasized that there’s not one infection rate for the state or for the entire country. Infection rates vary by geography, income, race, ethnicity and neighborhood.