The latest cases bring to 45 the number of people who have contracted the illness, the Wuhan Municipal Health Commission said Saturday. Five are in serious condition, two died and 15 have been discharged. The others are in stable condition.

The cause of the pneumonia has been traced to a new type of coronavirus.

Health authorities are keen to avoid a repeat of SARS, or severe acute respiratory syndrome, another coronavirus that started in southern China in late 2002 and spread to more than two dozen countries, killing nearly 800 people.

The U.S. announced Friday that it would begin screening passengers at three major airports arriving on flights from Wuhan. The Centers for Disease Control and Prevention said it would deploy 100 people to take the temperatures and ask about symptoms of incoming passengers at the Los Angeles, San Francisco and New York City's Kennedy airports.

At least a half-dozen countries in Asia have started screening incoming airline passengers from central China. The list includes Thailand and Japan, which have together reported three cases of the disease in people who had come from Wuhan. It  is an unusually busy travel period as people take trips to and from China around Lunar New Year, which falls on Jan. 25 this year.

Doctors began seeing a new type of viral pneumonia — fever, cough, difficulty breathing — in people who worked at or visited a food market in the suburbs of Wuhan late last month. The city's health commission confirmed a second death this week, a 69-year-old man who fell ill on Dec. 31 and died Wednesday.

Officials have said the pneumonia probably spread from animals to people but haven't been able to rule out the possibility of human-to-human transmission, which would enable it to spread much faster.

No related cases have been found so far among 763 people who had close contact with those diagnosed with the virus in Wuhan. Of them, 665 have been released and 98 remain under medical observation, the Wuhan health authorities said.