"We have to have something in place that is efficient and that we can rely on, and we're not there yet," Fauci, the nation's top infectious disease expert, said in an interview with the AP that was published Tuesday.

Fauci said opening the country on May 1 -- after federal social distancing guidelines are set to expire -- is "a bit overly optimistic" for many places in the US. This process, he said, would likely have to occur on a "rolling" basis and not simultaneously across the country. A key worry, he said, was that the US would see new outbreaks in places where officials may not be able to swiftly test and trace contacts of those who are infected.

Public health experts widely agree that to control the epidemic in the absence of strict social distancing measures, states and localities will need to build the capacity for contact tracing. That's a process of identifying new cases of Covid-19 and then tracking down and quarantining anyone who could have been infected by those newly identified cases.

Trump on Monday said he would "soon" release guidelines to governors on how to reopen the economy. The President has downplayed the need to improve the availability of testing in order to reopen the country.

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