Antibody tests are suddenly everywhere. These tests are designed to determine whether someone contracted the virus in the past. They help policy makers understand how the virus spreads, and whether measures to contain the virus are working.

Federal regulators relaxed guidelines to make it easier for companies to produce the tests, but this has allowed for a flood of unreliable--and sometimes fraudulent--tests to be offered to consumers. Now, Kristen V. Brown reports, the government is trying to control the mess.