Dr. Nancy Messonnier, director of the US Centers for Disease Control and Prevention’s National Center for Immunization and Respiratory Diseases, responded to a statement Sunday by the Chinese health minister Ma Xiaowei that people are infectious before they have symptoms of Wuhan coronavirus.

“We at CDC don’t have clear evidence that patients are infectious before symptom onset, but we are actively investigating that possibility,” she said.

Messonnier said the risk to the American public for contracting this virus continues to be low.

“We need to be preparing as if this is a pandemic, but I continue to hope that it is not,” Messonnier said.

The CDC confirmed Sunday there are five cases of Wuhan coronavirus in the United States – one in Arizona, two in California and two previously confirmed cases in Illinois and Washington. All five cases were in people who had recently traveled in Wuhan, China.

The CDC has about 75 people still under investigation because they might have the virus, and about 25 others who were found not to have the virus. The CDC is the only lab in the United States that tests for the virus.