Before revision:  Second, we discuss how to add standard matched case-control studies (separately for SARS-CoV-2 test-positives and  test-negatives ) by asking accompanying persons to the test facilities to become controls.
After revision:  Second, we discuss how to add standard matched case-control studies (separately for SARS-CoV-2 test-positives and test-negatives separately, yielding two additional case-control studies. We describe two different types of population control groups: one composed of accompanying persons to the test facilities to become controls.