WASHINGTON — Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told the House Appropriations subcommittee in Congress on Wednesday that it remains difficult to determine accurate mortality rates of the new coronavirus outbreak, given that we simply do not know yet how many have been infected with the disease.

Fauci and other representatives from the National Institutes of Health were scheduled to sit before Congress to discuss its budget requests for 2021. But amid the coronavirus outbreak, many representatives took the opportunity to grill Fauci on the latest developments.

"We don't know the denominator," Rep. Andy Harris, R-Md., noted to Fauci when asking whether mortality rates are reliable.

"You said it, sir," Fauci responded, before further explaining.

"If you look at the cases that have come to the attention of the medical authorities, in China, and you just do the math — the math is about 2%. If you look at certain age groups, certain risk groups, the fatality is much higher."

The Life Care Center of Kirkland, a skilled nursing care facility in Washington state, has become the center of a potential outbreak. At least five deaths in the U.S. have been traced back to Life Care, according to state and local health officials.

Amid continuing questions around the numbers, Harris asked Fauci about the accuracy numbers published by the World Health Organization on Tuesday stating the death rate is 3.4% globally.

Fauci said the administration was told on a recent call with WHO that it had elevated the mortality rate because there weren't as many asymptomatic cases as it thought.

"What we're hearing right now on a recent call from the WHO, this morning, is that there aren't as many asymptomatic cases as we think — which made them elevate, I think, what their mortality is," Fauci said.

In the U.S., the administration is still working to ascertain the full number of Americans infected by the disease. The administration has been hamstrung by a slow rollout of testing, making it difficult to track.

"I'm torn," Fauci said. "If we get enough data to have a big [numerator] it's gonna be bad news for us."

"You know as well as anybody that the mortality for seasonal flu is .1%," he added. "So even if it goes down to 1%, it's still 10 times more fatal."

— CNBC's Divya Verma contributed to this report.



