The World Health Organisation (WHO) has warned that it appears likely the novel coronavirus can be passed between people in close contact.
This comes after France confirmed a second case of a deadly new respiratory virus related to Sars, as they increased efforts to inform the public about how to avoid the illness and watch for its signs.
A hospital roommate of the 65-year-old man who initially contracted the virus tested positive for the illness. The second patient's condition has deteriorated, requiring treatment in intensive care, Health Minister Marisol Touraine said at a news conference. The minister added that the first patient is "in a stable but worrisome situation."
The virus is known to cause pneumonia and sometimes kidney failure.
Touraine said pamphlets listing precautionary measures and potential signs of illness will be available at French airports for travellers, especially those visiting the Arabian Peninsula, where many cases of the virus have been reported.
The novel coronavirus has killed 18 people since being identified last year, out of more than 30 confirmed cases reported to the WHO since September 2012. The first France patient had just returned from vacationing in Dubai on an organised tour when he fell ill.
The initial France patient shared a room with the second patient for a few days in late April at a hospital in Valenciennes. Now both are being treated at the Lille Hospital in northern France. Four other suspected cases, all people who had contact with the initial patient, were false alarms, officials said.
Most of those infected since the virus was identified had travelled to Qatar, Saudi Arabia, Jordan or Pakistan. There also have been cases in Britain and Germany.
The novel coronavirus is related to Sars, which killed some 800 people in a global epidemic in 2003, and belongs to a family of viruses that most often causes the common cold.
The virus is most closely related to a bat virus and scientists are also considering whether bats or animals such as camels or goats are a possible source of infection. Scientists are also considering whether fruit contaminated by animal droppings may have spread the virus.
A pamphlet advising travellers on measures to avoid getting sick, such as frequently washing hands or avoiding animals, is being made available at French airports. The pamphlets also list worrisome symptoms to watch for, such as fever.
Arnaud Fontanet of the Pasteur Institute, which is doing the testing for the virus in France, said at the news conference that the respiratory tract appears to be a dominant mode of transmission.
Officials are trying to track down all people who had contact with the second patient in France as well as all those who traveled to Dubai on an organized tour with the man initially diagnosed with the virus.
"Professionals, doctors, consider that there is no need for excessive worry, but once again we should be vigilant," the health minister said. "I am repeating: Nothing is being left to chance."