A middle-aged businessman from England who vacationed in the Alps has illustrated how the ease of international travel is complicating global efforts to track and contain the new coronavirus that emerged in China.

From the Singapore hotel where he is believed to have picked up the virus during a conference, to a ski resort in the French Alps and a pub in his hometown of Hove on the southern coast of England, as well as the flights he took on his way back to the United Kingdom, the man came in contact with dozens of other people, potentially infecting them before he was diagnosed and hospitalised.

Health officials are now hunting for them.

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Already, five Britons who stayed with him at a chalet in the Alps have been diagnosed with the virus, including a nine-year-old boy. Another man who stayed at the resort was discovered infected after returning to his home on the Spanish island of Mallorca.

The apparent ease with which virus spread raises concern that some of the 90 others who attended the conference may also have been infected and "may go on to initiate chains of infection in their home countries", said Dr Nathalie MacDermott, a clinical lecturer at King's College London.

The World Health Organization warned that given the relatively small cluster so far, it would be unfair and an exaggeration to characterise the businessman as a "super-spreader", or someone who infects an unusually large number of people. And this is by no means the only cluster seen in the outbreak.

Another small one, for example, was tied to a Chinese woman who travelled to a meeting at a German car parts company. The virus spread to a dozen employees and their family members in Germany.

But the case of this single traveller from England underscores the importance of quick cross-border information-sharing and detective work to find other people potentially exposed.

'For now, only a spark'

The virus has infected more than 40,000 people globally and killed over 900, with the overwhelming majority of cases in China. It is unclear exactly how it is transmitted, but experts think it is spread mostly by droplets when people cough or sneeze. Health officials warn that it can take up to 14 days for those who have been exposed to show symptoms.

Most people have only mild symptoms such as a fever and runny nose. But some develop pneumonia. Those who have fallen severely ill have been mostly over 60 with other health problems.

The WHO's director-general, Tedros Adhanom Ghebreyesus, said the spread of the virus among people - like the British businessman - who have not been to China is concerning.

"The detection of the small number of cases could be the spark that becomes a bigger fire, but for now, it's only a spark," he said. "Our objective remains containment. We call on all countries to use the window of opportunity we have to prevent a bigger fire."

The story of the British man begins with a business conference - like so many that take place all over the world, as multinational corporations and groups bring together employees, clients and others to share information, sell products and enjoy all-expenses-paid getaways.

The man, who has not been identified publicly, flew to Singapore for a January 20-22 event sponsored by his employer, Servomex. The company, based in a two-storey industrial building in the town of Crowborough, 35 miles south of London, makes industrial sensors sold around the world.

In a statement, Servomex said "a limited number of its employees in different countries have been diagnosed with the coronavirus and are now being treated."

Fast spread

The Grand Hyatt Singapore, a five-star hotel with 677 guest rooms, said Singapore's Ministry of Health informed it that three people who attended the conference experienced symptoms after returning to their home countries of Malaysia and South Korea and have now been diagnosed with the virus.

The hotel said 94 foreigners stayed at the Grand Hyatt at the same time as the Servomex conference, including people from Wuhan, the Chinese city at the epicentre of the outbreak. The hotel said it is now deep-cleaning guest rooms, meeting spaces, restaurants, the fitness centre and other public areas.

One of the people infected was the Hove man, who flew on to France before he started to display any symptoms. He reportedly joined his family for four days at a three-storey chalet in Contamines-Montjoie, a resort in the Mont Blanc region that offers downhill skiing from 25 lifts, well as cross-country skiing, skating and paragliding.

Jerome Salomon, head of France's national health agency, said that in the wake of the episode, 61 people, including many children who went to school with the boy, were tested and proved negative for the virus.

The businessman flew back to the UK on January 28 on an EasyJet flight from Geneva to London's Gatwick Airport. The airline did not disclose how many people were on board, but said England's public health agency was contacting all passengers who were seated near the man.

Once back in the UK, the businessman visited The Grenadier pub in Hove, which said it was told by the public health agency there was "minimal ongoing risk of infection" to guests or staff.

A school in the community, Portslade Community Academy, said one its students had been told to "self isolate", the local Brighton Argus newspaper reported.

"It does appear that the index case has passed on the infection to an unusually large number of contacts," said Dr Andrew Freedman, an expert on infectious diseases at Cardiff University. "As such, he could be termed a 'super-spreader'."

During the 2002-03 SARS outbreak, the deadly disease made its way to the wider world after a Chinese doctor who had treated patients on the mainland checked into a Hong Kong hotel.

He ultimately infected six other hotel guests staying on the same floor, possibly when he sneezed or coughed as they were waiting for a lift, according to Hong Kong health authorities. Some of those guests then took SARS to Canada, Taiwan, Thailand and Singapore, seeding new outbreaks.

But Dr Michael Ryan, WHO's emergencies chief, said: "It's way too early and much more of an exaggeration to consider the Singapore conference event a super-spreading event."