FILE - In this illustration provided by the Centers for Disease Control and Prevention (CDC) in January 2020 shows the 2019 Novel Coronavirus (2019-nCoV). This virus was identified as the cause of an outbreak of respiratory illness first detected in Wuhan, China. A woman in the San Francisco Bay Area who became ill after returning from a trip to China has become the ninth person in the U.S. to test positive for a new virus, health authorities said Sunday, Feb. 2, 2020. (CDC via AP, File)

FILE - In this illustration provided by the Centers for Disease Control and Prevention (CDC) in January 2020 shows the 2019 Novel Coronavirus (2019-nCoV). This virus was identified as the cause of an outbreak of respiratory illness first detected in Wuhan, China. A woman in the San Francisco Bay Area who became ill after returning from a trip to China has become the ninth person in the U.S. to test positive for a new virus, health authorities said Sunday, Feb. 2, 2020. (CDC via AP, File)

FILE - In this illustration provided by the Centers for Disease Control and Prevention (CDC) in January 2020 shows the 2019 Novel Coronavirus (2019-nCoV). This virus was identified as the cause of an outbreak of respiratory illness first detected in Wuhan, China. A woman in the San Francisco Bay Area who became ill after returning from a trip to China has become the ninth person in the U.S. to test positive for a new virus, health authorities said Sunday, Feb. 2, 2020. (CDC via AP, File)