The World Health Organization says there is so far no evidence that a new strain of bird flu is easily spreading among humans in China.
Michael O'Leary, the chief of the WHO office in China, said Friday that the evidence suggests that poultry is a vehicle for transmission, but researchers have not been able to establish a clear and strong link.
On Thursday, Feng Zijian, a director at the Chinese Center for Disease Control and Prevention, said human-to-human transmission of the H7N9 strain is possible in theory, though highly sporadic.
China has reported 17 deaths since the virus was reported in humans for the first time last month. In total, 82 people have been infected, most near Shanghai.
Until now, the virus was believed to have only been transmitted from birds to humans, greatly limiting its ability to spread. But officials say 40 percent of those infected appear to have had no contact with poultry.
Chinese authorities are investigating whether long-term and unprotected exposure to an infected person, such as a family member, might result in a person-to-person transmission.
China has been working on developing vaccines and other treatment for the virus, as part of a wider plan to combat any potential outbreak. It has also slaughtered thousands of birds and closed many poultry markets in an attempt to slow the spread of the disease.
This is believed to be the first time humans have contracted the H7N9 bird flu virus. It previously existed only in birds. The more common strain of avian flu, H5N1, has killed more than 360 people worldwide in the last decade.
China is considered one of the countries at greater risk for bird flu because it has the world's biggest poultry population and many chickens in rural areas are kept close to humans.