The United States’ top infectious disease doctor wants a team of disease detectives from the US Centers for Disease Control and Prevention to go to China and check on crucial questions about how the Wuhan coronavirus is spreading. 

But there’s one problem: China first has to invite the CDC.

“Up to now, to my knowledge, we have not been invited,” said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases at the US National Institutes of Health.

A CDC spokesperson was not immediately available to comment on Sunday. NIH and CDC are separate divisions of the US Department of Health and Human Services.

On Sunday, Ma Xiaowei, China’s health minister, told reporters that the virus could spread before someone develops symptoms. If so, that means the virus will spread much more quickly than expected.

Ma did not explain how Chinese authorities arrived at this conclusion.

Fauci said that CDC disease detectives would need to see precisely how Chinese health authorities have gathered their data.

“To my knowledge, we have not seen the precise minute, granular data and how they collected it,” he said. “We need to get to the real bottom line of how they collected their data and see if it’s valid.”

“The Chinese have good people. I don’t want to impugn their capabilities,” Fauci added. “But when it’s something as important as this, our people who are trained epidemiologists need to go over their data and the best way to do that is go there and see how they’re collecting it.” 

He added that to his knowledge, the Chinese did not tell US health authorities that the virus could spread before someone is symptomatic, a crucial aspect of any disease investigation. He said he learned about it after reading a CNN reporter’s email.