Public health experts have called for increased testing to get a clearer picture of the pandemic's scope, as well as to identify, isolate and trace contacts for infected patients.

High rates of positive results could mean there's not enough testing, Fauci said, adding that those should constitute "maybe less than 10 percent." The U.S. currently is seeing positive rates closer to 20 percent.

Adequate testing should "get those who are infected out of society so that they don’t infect others," he said.

Fauci warned public health groups not to get fixated on the number of tests needed. What's more important is whether "you have enough tests to respond to the outbreaks that will inevitably occur as you try and ease your way back into the different phases," he said.

Rapidly scaling up testing could be complicated by supply chain challenges, and will require careful national coordination, as POLITICO has reported.

Fauci emphasized that his comments applied to diagnosing active infections and not to the antibody tests that can reflect if a patient was previously infected with the virus.

The U.S. has seen more than 915,500 cases and over 51,600 deaths, Fauci noted during the webcast.

