Can we use serologic testing to find out the incidence of SARS-CoV-2 infection in a population?

Bottom Line

Serologic testing estimates that at the time of the study, about 367,000 adults in Los Angeles County may have had antibodies to SARS-CoV-2, despite only having 8,430 confirmed cases in the area.


Sood, N. et al. Seroprevalence of SARS-CoV-2–Specific Antibodies Among Adults in Los Angeles County, California, on April 10-11, 2020. JAMA (2020). DOI: 10.1001/jama.2020.8279

Date Published:

18 May 2020


Serologic testing means looking for the presence of antibodies in a person’s blood that may have formed against a certain infectious agent. Right now, most reporting of COVID-19 cases occurs through the testing of symptomatic patients, missing many individuals who may have few or no symptoms, or who were not tested due to lack of availability. This is a challenge and limitation to public health response and planning, making it important to investigate other methods of tracking infectious cases such as through serologic testing. In this study, participants were recruited through a market research firm and were randomly invited to participate based on age, sex, race/ethnicity, and income quota sampling. This study used antibody testing to determine the extent of the presence of SARS-CoV-2-specific antibody in Los Angeles County, California from April 10-14, 2020. 863 residents agreed to participate. After adjusting for test sensitivity and specificity, the weighted rate of presence of antibody (seroprevalence) was 4.7% (2.5%-7.1%), suggesting much greater spread than the rates reported from testing symptomatic individuals.

Summary by: David Lee