WASHINGTON (BLOOMBERG,)Dr Anthony Fauci, the US top infectious-disease expert, said that a gathering in the White House Rose Garden the previous month was a "super-spreader event" for the novel coronavirus.
Dr Fauci also said US President Donald Trump's talk about an experimental Covid-19 treatment he received as "a cure", may cause "confusion".
Mr Trump held a ceremony in the White House Rose Garden on Sept 26 to honour Supreme Court nominee Amy Coney Barrett. While the White House had a testing regime in place to screen for virus cases, few guests wore masks and attendees mingled and sat in close proximity to one another both indoors and outdoors.
Subsequently, the president and several top staffers, as well as senators and military officials, have tested positive for the novel coronavirus.
"The data speak for themselves," Dr Fauci said in an interview Friday with CBS News Radio.
"We had a super-spreader event in the White House. And it was in a situation where people were crowded together, were not wearing masks. So the data speaks for themselves."
Dr Fauci said in the interview that people who are infected with the coronavirus but aren't yet showing symptoms can transmit the pathogen to others, which makes the case for wearing face coverings.
Asymptomatic individuals "are a substantial part of the people that actually transmit infections to other people," Dr Fauci said in the CBS interview.
"So the better part of the recommendation would be everybody wear a mask, literally universally."
Asked about Mr Trump's effusive praise for Regeneron's antibody treatment, Dr Fauci said that talking about a "cure" could be misleading because it hasn't yet been proven, and the drugs that are currently available have only been shown to have modest to moderate results.
"We don't have any indicationI think you really have to depend on what you mean by a cure, because that's the word that leads to tons of confusion," he said.
He then walked through some of the medicines that are currently recommended or have been temporarily approved against the disease.
These include the antiviral remdesivir which has been shown to diminish time to recovery among hospitalised patients, and the steroid dexamethasone, which reduces mortality rates in patients who need supplemental oxygen.
Regeneron's treatment belongs to a class of drug called monoclonal antibodies.
Dr Fauci said that while these had been "showing promise in clinical trials," the research is still ongoing and no final determination has been made.
Mr Trump was hospitalised the previous week after testing positive. On Saturday (Oct 10), he plans to hold his first in-person event at the White House since leaving the hospital, despite questions about how far along he is in his recovery.
He has released videos in recent days saying he is well, and his doctor said in a statement on Wednesday that Mr Trump had been free of symptoms for the previous 24 hours.
The president has been given several experimental Covid-19 therapies, including Gilead Sciences Inc. antiviral remdesivir, the steroid dexamethasone and an antibody cocktail made by Regeneron Pharmaceuticals Inc.
Mr Trump said he intends to grant an emergency-use authorisation to the Regeneron drug, which hasn't yet been cleared in any form by US regulators.