Americans from China virus zone evaluated at military base

An airplane carrying U.S. citizens being evacuated from Wuhan, China, lands at March Air Reserve Base in Riverside, Calif. Jan. 29, 2020. The passengers will undergo additional screenings in California and be placed in temporary housing. Officials have not said how long they will stay there. (AP Photo/Ringo H.W. Chiu)

A U.S. Air Force plane sits at the March Field Air Museum near March Air Reserve Base in Riverside, Calif. Jan. 29, 2020. An airplane carrying U.S. citizens being evacuated from Wuhan, China, will take off at March Air Reserve Base this morning. (AP Photo/Ringo H.W. Chiu)

A nearly empty lobby at the North Terminal of the Ted Stevens Anchorage International Airport in Anchorage, Alaska, is shown Tuesday, Jan. 28, 2020. A plane evacuating U.S. citizens from Wuhan, China, because of a virus outbreak was expected to land Tuesday evening for refueling at the terminal normally only used in the summer for international flights before carrying on to California. The people are standing in line at an Alaska DMV satellite office. (AP Photo/Mark Thiessen)

Personnel in protective clothing unload luggages from the airplane carrying U.S. citizens being evacuated from Wuhan, China, at March Air Reserve Base in Riverside, Calif. Jan. 29, 2020. The passengers will undergo additional screenings in California and be placed in temporary housing. Officials have not said how long they will stay there. (AP Photo/Ringo H.W. Chiu)

RIVERSIDE, Calif. — The 201 Americans evacuated from the Chinese city at the center of the virus outbreak are undergoing three days of monitoring at a Southern California military base to make sure they do not show signs of the virus, officials said Wednesday.