The United States has been criticised for early missteps and a delayed response to the coronavirus outbreak, allowing the virus to spread undetected there.
A report published in the Journal of the American Medical Association on Monday said the limit of the number of people tested and problems with testing equipment have slowed the country's fight against Covid-19.
"In the early stages, Covid-19 has spread beyond the nation's ability to detect it," a team of Stanford University experts wrote.
They said state laboratories also encountered difficulty verifying the results – the reasons for which remain under investigation.
It references a woman who was infected in California and refused a test for the virus because she had not travelled to China, where the outbreak began in December.
"The CDC also initially limited access to testing to a narrow group of individuals with known exposure. The delayed discovery of a case of Covid-19 in California, followed quickly by evidence of community transmission in multiple states, revealed the shortcomings of this strategy," the report said.
The woman was tested and confirmed to have the virus in the first-known case of community transmission in the United States.
The report said that widespread testing, even for patients with mild symptoms, could overwhelm the health industry and make it more difficult for patients with severe symptoms to get proper treatment.
The US Government has criticised China's early efforts to contain the disease, accusing Chinese officials of not being open about the spread at its onset.
Last week, Secretary of State Mike Pompeo accused the country of sharing inadequate information that put the US "behind the curve" for dealing with the virus.
But the Trump administration has been slammed for its own handling of the disease, after Vice President Mike Pence, who has been tasked with leading the US response to the disease, admitted last week that there were not enough diagnostic tests to meet demand.
Trump this afternoon announced he is sharply restricting passenger travel from 26 European nations to the United States and moving to ease the economic cost.
But he left unaddressed testing, the backlog that is hampering efforts to learn just how many Americans already are infected.
After days of playing down the threat of the virus, Trump blamed Europe for not acting quickly enough to address the novel coronavirus and claimed that US clusters were "seeded" by European travellers.
"We made a lifesaving move with early action on China," Trump said. "Now we must take the same action with Europe."
However Trump said the restrictions won't apply to the United Kingdom, and there would be exemptions for "Americans who have undergone appropriate screenings." It also wouldn't apply to cargo.
He said the US would monitor the situation to determine if travel could be reopened earlier.
Earlier he had tweeted he was "fully prepared to use the full power of the Federal Government to deal with our current challenge of the CoronaVirus!"
Fallout from the spreading coronavirus, which gives flu-like symptoms and has claimed more than 4500 lives worldwide, has extended into acute difficulties for parts of the economy and a tanking stock market.
Trump, who has come under criticism for his response to the crisis, made his comments while meeting with US bank leaders on ways of assisting consumers and small businesses.
He said "we'll be doing a lot of additional work with small businesses … many billions of dollars."
Trump this afternoon said he was also directing agencies to provide unspecified financial relief for "for workers who are ill, quarantined or caring for others due to coronavirus," and asked Congress to take action to extend it.
Trump said the US will defer tax payments for some individual and business filers for three months to lessen the impacts of the virus outbreak.