US authorities have joined others by starting to screen passengers from China for symptoms of a new virus causing concern globally that a disease health officials do not yet fully understand could spread during a key holiday period. The new virus, which was discovered in the central Chinese city of Wuhan, belongs in the same large family of coronaviruses that includes Severe Acute Respiratory Syndrome (SARS), which killed nearly 800 people globally during a 2002-03 outbreak that also started in China. Though experts say the new virus does not appear to be as lethal as SARS, there is little known about its origins and how easily it can spread. The World Health Organization (WHO) has also warned that a wider outbreak is possible, though it has advised against any travel restrictions for China. Nearly 50 people are now known to have been infected globally, but all of them either live in Wuhan or have travelled to the city. China reported four more cases of pneumonia believed to be caused by a new coronavirus strain The Wuhan Municipal Health Commission (WMHC) said on Saturday the four new individuals diagnosed with the new virus are in stable condition, adding it has confirmed 45 cases in the city as of Thursday. A day earlier, the commission confirmed the death of a second patient. People in Wuhan said that while many are reviewing travel plans as a precaution, general anxiety over the virus is low. Businesses are operating normally in the city, which has a population of over 8 million, they said. Gyms, pools, transport hubs and food markets contacted said they had not made changes or taken extra precautions. More than 400 million Chinese people are expected to make 3 billion trips over the new year beginning on January 24, mostly migrant workers returning to their home towns. However, many Chinese also use the holiday to go overseas. A person who works for China's official train ticketing service said that there were no additional health screening measures or temperature checks in place at Wuhan train stations. Since Wednesday, people travelling from Wuhan's Tianhe International airport have been subject to temperature tests before boarding flights, according to an official notice. Two flight attendants staffing separate domestic flights in and out of the city said they had not received additional training or warnings about the virus. But people who have been affected are worried. "I look at a public handrail or food or people standing close together and it makes me feel anxious," said a 33-year-old woman whose last name is Peng, who lives roughly one km from the seafood market where the virus is suspected to have originated and says her elderly aunt was hospitalised with flu-like symptoms late last week. The illness is not a confirmed case of coronavirus, she said by phone, but two relatives cancelled plans to visit the pair for the new year. Ms Peng declined to share her full name because hospital authorities and police have warned Wuhan residents against speaking about the virus online or to media. "There is no holiday for me ... only worry," she said. Thailand and Japan have confirmed new cases earlier this week, stoking worries globally as many of the 1.4 billion Chinese people will travel during the Lunar New Year holidays that begin next week. US aviation authorities said they would start screening at three airports to detect travellers arriving via direct or connecting flights from Wuhan who may have symptoms of the new virus. In Asia, authorities in Singapore, South Korea, Taiwan and Thailand have stepped up monitoring of passengers from Wuhan at airports. Indonesia, Malaysia and the Philippines say they have strengthened screening at all points of entry in response to the outbreak, as well. A report published by the London Imperial College's MRC Centre for Global Infectious Disease Analysis said there are likely to be "substantially more cases" of the new coronavirus than currently announced by Wuhan authorities. The college’s scenario estimate that there would be 1,723 cases showing the onset of related symptoms by January 12. But Alexandra Phelan, global health legal expert at Georgetown University's Centre for Global Health Science and Security, said such screening may be insufficient in preventing the virus from spreading as its symptoms, which include fever, cough and difficulty in breathing, are "quite general". "There are likely to be many individuals with matching symptoms due to an illness that is not 2019-nCoV," Ms Phelan said, referring to the new virus.