I heard testing done in the community in April showed that more people may have been infected than we realized – does that mean the death rate may be lower than we realized?

We know that coronavirus can cause mild and even asymptomatic infections in many people.  Antibody testing, also referred to as serology testing, can help inform our understanding of coronavirus infection prevalence and identify those who have already been exposed. 

An interesting study out of Stanford recruited 3300 residents of Santa Clara County for serology testing over the weekend of April 3rd to estimate the percentage of the county that had been infected with COVID.  The study estimates as many as 81,000 people could have been infected, or between 2.5 to 4.2% of residents.  If true, this would suggest the death rate may actually be much lower than previously thought.  The study, which is still in pre-publication phase, has received a lot of criticism, mostly focused on biases in recruitment (which was done through social media platforms such as Facebook and was likely subject to bias – patients most worried about prior symptoms would be more likely to sign up) and on the error rates of the test kits used (even a small false positive rate could account for much of the findings – while the study authors argue they controlled for the known false positive rate of the test in their projections, many statisticians feel this was not adequate). This study helps to show that more studies are needed to provide a reliable picture of community prevalence. (April 24, 2020)