CDC is working with commercial laboratories to conduct large-scale geographic seroprevalence surveys to estimate the percentage of people who were previously infected with SARS-CoV-2, the virus that causes COVID-19 disease. The strategy involves working with state, local, territorial, academic, and commercial partners to better understand COVID-19 in the United States using serology (antibody) testing for surveillance (“seroprevalence surveys” or “serosurveys”). For the surveys, de-identified clinical blood samples are tested for antibodies to SARS-CoV-2.