The United States will see more cases of the coronavirus, Dr. Anthony Fauci, the head of the National Institute of Allergy and Infectious Diseases, told Congress on Wednesday.

“The bottom line, it’s going to get worse,” Fauci said when asked during a House Oversight Committee hearing if “the worst is yet to come.”

He explained that because of the cases of community spread — cases where people don’t know how they became infected — and travel-related cases, it would become hard to track infected individuals and contain the outbreak.

“When you have enough of that, then it becomes a situation where you’re not going to be able to effectively and efficiently contain it,” he added.

Watch the video below:

.@RepMaloney: "Is the worst yet to come?"



Dr. Anthony Fauci: "Yes, it is…We will see more cases and things will get worse than they are right now…Bottom line: it's going to get worse."



Watch full #Coronavirus hearing here: https://t.co/qUfpOTAqTq pic.twitter.com/RNBNiPrFN1 — CSPAN (@cspan) March 11, 2020

Oversight Chair Carolyn Maloney (D-N.Y.) asked Fauci if it is the case that a lack of testing would make it harder to track the spread of the outbreak. Fauci said it would make it harder, but added that testing for the virus is ramping up across the country.

Along with testing people who go to their doctors or hospitals to be tested, Fauci said the Centers for Disease Control and Prevention (CDC) is starting “surveillance” testing — where officials proactively test individuals before they seek testing — in six cities and plans expand that to other cities across the country.

Additionally, Fauci said that if the government doesn’t handle the outbreak properly, “many, many millions” of Americans could be infected by the coronavirus. When asked about an estimate on the numbers, he responded:

“I can’t get you a realistic number until we put into the factor of how we respond. If we are complacent and don’t do really aggressive containment and mitigation, the number could go way up to many, many millions.”

While some believe the threat of the coronavirus is “exaggerated,” Fauci warned that even if the mortality rate of the virus is one percent, it is still a decent amount higher than the seasonal flu and should not be taken lightly.

“We have to change our behavior. We have to basically assume that we’re going to get hit,” he said.