The most recent information I could find regarding Contra Costa County is that there have been 20 deaths out of 693 reported cases. That is from the Mercury News website published yesterday and updated within the last hour.
https://www.mercurynews.com/2020/04/19/coronavirus-contra-costa-county-reports-seven-new-cases-one-death/
Dividing 20 by 693 results in a
per capita rate of 0.02886.
The commonly cited 'death per reported case' rates for Covid-19 on a large scale are somewhere in the 3.0% to 4.0% range with the most typical number I have seen as 3.4%.
“
Globally, about 3.4% of reported COVID-19 cases have died. By comparison, seasonal flu generally kills far fewer than 1% of those infected.” [Empahsis in the original.]
https://www.worldometers.info/coronavirus/coronavirus-death-rate/
That number is
per cent, or per 100, as opposed to the
per capita, or per individual figure I calculated above for Contra Costa County. To convert THAT figure to percentage, you multiply it by 100, (or move the decimal point two places to the right as we learned, oh, so long ago,) resulting in a percentage for Contra Costa County of 2.886%.
So, not as bad as the generally quoted figure for Covid-19 worldwide, but certainly much higher than "the less than 1%" accepted rate for the flu.
Now THAT is using the numbers provided. We could use up all of this website’s storage pointing out problems with arriving at the numbers…poor reporting, poorly defined standards on just what constitutes actually being infected with the virus, failure to report due to mistake, failure to report due to intentional concealment, poorly defined standards on just what constitutes the cause of death, lack of testing, sample size, …. the list goes on.
[And I have NO experience in medicine, epidemiology, etc., and when I took statistics back in the early 70s to complete a breadth requirement we did all of our calculations with pencil and paper.]