In addition to Fauci, U.S. Centers for Disease Control and Prevention Director Dr. Robert Redfield and Admiral Brett Giroir, assistant secretary at the Department of Health and Human Services, also testified.
During the hearing, Fauci was been asked about why the Europe did better job than the U.S.in the aspect of containing COVID-19.
Early in the session, Fauci clashed with Rep. Jim Jordan, after the Ohio Republican demanded Fauci's opinion about whether protests should be curbed or eliminated to control the pandemic.
Fauci has estimated that only about half of the US stayed home, allowing the virus to continue infecting people at exponential rates and overwhelming many hospitals, particularly across the South.
As a result, the United States' baseline of transmission was higher than Europe.
Based on the number of positive coronavirus tests in those states, they "are starting to have that very early indication" of a surge, he said.
Responding to questioning by a House Democrat, Fauci says the scale of the USA outbreak is the result of multiple factors, including some states opened too quickly, disregarding federal guidelines. "You have mucosa in the nose, mucosa in the mouth, but you also have mucosa in the eye", Fauci told ABC News "Theoretically, you should protect all the mucosal surfaces".
"That study is a flawed study, and I think anyone who examines it carefully is that it is not a randomized placebo-controlled trial".
Fauci's warning came as the US' COVID-19 death count has surpassed 150,000. "The thing we're extraordinarily confident about is that we're going to see this in the next few years".
House subcommittee Chair James Clyburn, a Democrat from SC, addressed President Trump's tweet that seemed to reference a chart Clyburn showed earlier in the hearing about U.S. cases largely outpacing European countries.
Arizona is a state "headed in the right direction" with a downward trend since early July, Gov. Doug Ducey said Thursday.
Democrats say they intend to examine the "urgent need for a national comprehensive plan" to address the pandemic, according to a news release sent by the Select Subcommittee on the Coronavirus Crisis, which is chaired by House Majority Whip James Clyburn.
People in states that didn't follow the guidelines ignored guidance on wearing masks, avoiding crowds, and maintaining at least six feet from non-household members, Fauci added, saying: "Hopefully as we're going forward we can turn this around".
He said controlling the outbreaks will require people to wear masks, avoid crowded indoor spaces and wash their hands frequently.