TONIGHT, A RED FLAG FOR FOUR PEOPLE ABOARD THAT PLANE.

CENTERS FOR DISEASE CONTROL NOT TAKING ANY CHANCES.

>>>> WE ARE BEEN VERY AGGRESSIVE , USING QUARANTINE MEASURES WE HAVE NOT USED FOR 50 YEARS TO CONTROL THIS.

WALTER: THE DOCTOR SAYS THE MOVE TO SEND FIVE QUARANTINED EVACUEES TO THE HOSPITAL IS PRECAUTIONARY.

>> THERE IS A NUMBER OF REASONS THAT PEOPLE COULD HAVE THESE TYPES OF SYMPTOMS, NOT ONLY THE CORONAVIRUS.

THEY ARE TESTED AND EVALUATED FOR ALL SORTS OF DIFFERENT DISEASES.

WALTER: THE GROUP OF FIVE HAS NOT BEEN DIAGNOSED WITH CORONAVIRUS, BUT IS SHOWING SYMPTOMS OF IT.

CORONAVIRUS IS A VIRAL RESPIRATORY ILLNESS FIRST IDENTIFIED IN WUHAN, CHINA.

IN MORE SEVERE CASES, INFECTION CAN CAUSE PNEUMONIA AND EVEN DEATH.

HUNDREDS OF AMERICAN EVACUEES FROM A WUHAN WERE FLOWN TO TRAVIS AIR FORCE BASE ON TWO FLIGHTS THIS WEEK.

OFFICIALS TELL US FOUR PEOPLE ON BOARD THIS MORNING'S FLIGHT IS AMONG THE SYMPTOMATIC GROUP.

ONE PERSON IN THE GROUP WAS ABOARD WEDNESDAY'S FLIGHT.

CORONAVIRUS IS SPREAD WHEN UNINFECTED PERSON KOSTER SEIZES -- AN INFECTED PERSON COUGHS OR SNEEZES.

>> IN EACH OF THOSE CASES, WE ARE ABLE TO GET THEM TO THE APPROP