HONG KONG -- Fears are rising that the newly identified coronavirus that broke out in the central Chinese city of Wuhan will spread across Asia like the SARS epidemic nearly two decades ago.
Health officials have confirmed that the infection can be passed from person to person. Authorities in Beijing and beyond are expanding screening at transport hubs as hundreds of millions of Chinese citizens are preparing to travel domestically and overseas during the Lunar New Year holiday, which starts this weekend.
Travel into and out of Wuhan, a city of 11 million people, and other cities in Hubei Province has been restricted in an attempt to keep the virus from spreading further.
Chinese President Xi Jinping on Monday instructed state officials to prioritize "the safety and health of people" and ordered "resolute efforts" to stop the spread of the virus.
The virus causes pneumonia in those who contract it. Seventeen deaths are reported so far in China, with more than 500 people infected to date, according to the Chinese government. But symptoms appear less severe than those seen during the SARS outbreak nearly two decades ago.
Here are five things you need to know about the new respiratory infection.
What is it? How did it start?
Chinese officials identified the cause of the pneumonia as a new strain of coronavirus from the same family as severe acute respiratory syndrome. SARS killed more than 900 people during an outbreak that began in 2002, according to the World Health Organization.
Patients infected with the new coronavirus typically show symptoms such as fever, cough and breathing difficulties, with acute respiratory distress syndrome in severe cases.
How the virus spread to humans is unclear, but both WHO and Chinese officials regard an animal source as most likely. Chinese investigators confirmed that most of the initial patients visited a seafood and wildlife market in Wuhan, which was shut down in early January. The first case appeared last month in the city.
How far has it spread?
The new coronavirus has spread to Beijing and southern China's Guangdong Province, as well as to Thailand, South Korea, Japan, the U.S., Taiwan, Singapore and Vietnam as of Jan. 23.
How easily can the virus be transmitted from person to person?
Experts commissioned by China's health authorities confirmed Monday at least two cases of human-to-human transmission in Guangdong. Neither patient traveled to Wuhan, contracting the virus instead from family members who went to the area. Medical staff also were infected.
A WHO spokeswoman in Manila also told Nikkei on Monday that "according to the latest information received and WHO analysis, there is evidence of limited human-to-human transmission."
But no clear evidence shows sustained transmission, she said, in which the virus spreads easily among people beyond clusters such as family members and co-workers.
Could it be the new SARS? Is it just the beginning?
Though SARS had a fatality ratio of 11%, the new coronavirus appears less deadly and infectious. The four people who died were all older than 60.
But scholars suspect cases are underreported. A study by Imperial College London estimated more than 1,700 people were infected by Jan. 12 in Wuhan.
Professor Neil Ferguson, one of the report's authors, told Nikkei that people with milder symptoms -- which may be mistaken for a cold or flu -- might not seek treatment and may not be counted. The delay between infection and detection of the respiratory illness averages 10 days.
"While it would make controlling spread more difficult, it would mean that severe disease only happens rarely -- meaning this virus might pose less of a public health threat than some currently worry about," he said.
What should people do to protect themselves?
The WHO recommends maintaining basic hand and respiratory hygiene and avoiding close contact with anyone coughing and sneezing. Those who develop symptoms themselves, including difficulty breathing, should avoid traveling and seek medical treatment, and share travel history with their health care providers.
While the WHO has introduced no restriction on travel or trade regarding Wuhan, Chinese health experts advise avoiding travel to Wuhan, while residents of the city should avoid traveling elsewhere. They also recommend wearing masks and getting adequate sleep.