US health officials have rowed back on controversial advice issued last month that said people without Covid-19 symptoms should not get tested.
The Centers for Disease Control and Prevention (CDC) now says anyone in close contact with a known infected person should take a test.
Friday's "clarification" returns the CDC's stance on testing to its previous guidance, before the August alteration.
Reports said the controversial advice had not been given by scientists.
Sources quoted by the New York Times said it had been posted on the CDC website despite experts' objections.
Most US states had then rejected the guidance, Reuters reported, in a stinging rebuke to the nation's top disease prevention agency.
Some observers suggested the controversial move could have reflected a desire by President Donald Trump to reduce the growing tally of Covid-19 cases.
At a rally in June, Mr Trump told supporters he had urged officials to "slow the testing down, please". A White House official dismissed the remark as a joke.
However, administration officials denied any political motive, telling Reuters that the change reflected "current evidence and best public health practices".
Experts welcomed the change of tack on Friday.
"The return to a science-based approach to testing guidance from the Centers for Disease Control and Prevention is good news for public health and for our united fight against this pandemic," said Thomas File, president of the Infectious Diseases Society of America.
In its "overview of testing" for healthcare workers the CDC now says: "Due to the significance of asymptomatic and pre-symptomatic transmission, this guidance further reinforces the need to test asymptomatic persons, including close contacts of a person with documented SARS-CoV-2 infection."
It advises people to take a test "if you have been in close contact, such as within 6ft of a person with documented SARS-CoV-2 infection for at least 15 minutes and do not have symptoms".
The US has recorded nearly seven million cases of coronavirus, more than a fifth of the world's total. It has the world's highest death toll, with nearly 200,000 fatalities.