The state and the federal Centers for Disease Control and Prevention plan to conduct antibody surveys in Fulton and DeKalb counties to try to pinpoint who might have had COVID-19 and better understand the spread of the disease.

The state Department of Public Health said Atlanta-based CDC and the local health boards in both counties will visit randomly selected households from Tuesday through May 4 seeking volunteers to give blood samples for the antibody tests. Only households approached by the investigative teams will be allowed to participate, a news release said.

COMPLETE COVERAGE: CORONAVIRUS IN GEORGIA

Antibodies are an immune response to infection, and the presence of them suggests the person was infected with the virus whether they showed symptoms or not. Antibody testing for the disease does not detect active cases. But antibody tests are a critical tool to show how the disease spread through the population.

Antibody testing differs from diagnostic testing, which tries to determine active cases. Diagnostic testing has been limited in Georgia and most states, and many who likely had the disease over the past several weeks have not been tested.

“We encourage everyone who is visited by the teams to participate in this very important survey that can help public health officials assess how widespread COVID-19 is in certain areas,” said Georgia’s public health commissioner, Dr. Kathleen E. Toomey. “This is another way that Georgians can play a role in helping fight this virus.”