Advisers to the Centers for Disease Control and Prevention are concerned about a lack of data from China about the Wuhan coronavirus.
They say the dearth of information is curtailing international efforts to quell the outbreak.
Advisers commended the Chinese researchers for mapping the virus's genome in just a few weeks.
However, they said there's a glaring lack of basic epidemiological evidence about who's getting infected with the virus and how it's spreading.
This is Epi 101. I don't want to denigrate our Chinese colleagues, but when information is not presented clearly, you have to wonder. Dr. William Schaffner, CDC Adviser Medical Director, National Foundation for Infectious Diseases
The outbreak has grown quickly. Less than three weeks after the first case were reported, there are more than 600 cases.
The CDC advisers say as there's no vaccine against this new virus, public health efforts are crucial.