Today officials from the Centers for Disease Control and Prevention (CDC) warned that although the agency is taking historic measures to slow the introduction of COVID-19 into the United States, the country should prepare for the possibility of community spread, as seen in China and neighboring Asian countries.

"The day may come when we may need to implement such measures as seen in Asia," Nancy Messonnier, MD, director of the CDC's National Center for Immunization and Respiratory Diseases, said in a press conference, referencing the closing of businesses, schools, and churches in multiple countries where transmission is now occurring within the community.

Repatriated Diamond Princess passengers

The remarks were made just one day after 14 American passengers who tested positive for the virus and were on the Diamond Princess cruise ship docked in Japan were flown to the US for further medical treatment, on chartered flights with healthy passengers.

A total of 300 Americans who were aboard the Diamond Princess were repatriated on two flights chartered by the State Department this week. All passengers will be subjected to a 14-day quarantine upon their return to the United States.

Media reports yesterday suggested the CDC did not approve of the movement of the sick passengers to the United States, but the transport was ordered by the State Department. In the Washington Post, reporters quoted sources saying the decision to fly the sick passengers was a nightmare scenario.

Messonnier said the CDC will now track US cases of the novel coronavirus in two subsets to help quickly determine if community spread is taking place. Patients will be grouped into either a "repatriated" category or a separate category that represents cases related to individual travel or close case contact.

"We are keeping track of cases from repatriation because we do not believe those numbers accurately represent the picture of what is happening in the community," Messonnier said.

California reports new case

As of today, the CDC said there have been 21 COVID-19 cases in repatriated Americans, including 18 in Diamond Princess passengers, and another 13 US cases related to travel or case contact, for a total of 31.

Yesterday the University of Nebraska Medical Center confirmed that 11 of 13 Diamond Princess passengers tested positive for the coronavirus. Also yesterday, Providence Sacred Heart Medical Center in Spokane also confirmed four Americans aboard the cruise ship who had the virus would be treated at that facility.

Messonnier also said some Americans who were aboard the Diamond Princess are currently hospitalized in Japan, including some who are in serious condition. So far two Japanese passengers from the cruise ship who had COVID-19 died.

The latest US case not linked to the Diamond Princess was confirmed in Humboldt County, California, yesterday and involves a patient who had recently traveled to mainland China. This marks the seventh case in California. There have also been single confirmed cases in Massachusetts, Washington state, Arizona, and Wisconsin. Illinois has reported two cases.

A close contact of the Humboldt County patient also has symptoms, county officials said. Both the contact and the case-patient are doing well and self-isolating at home, according to the county's public health department.