There is no proof that the H7N9 bird flu virus is being transmitted between people in China, the World Health Organization said Monday, despite several members of a family falling ill in Shanghai.
China announced just over a week ago that the virus had been found in humans for the first time, and the number of confirmed cases has since risen to 21, with six deaths.
"Although we do not know the source of infection, at this time there is no evidence of sustained human-to-human transmission," Michael O'Leary, the WHO's representative in China, told a news conference in Beijing.
Concerns over human transmission arose after the two sons of an elderly man in Shanghai, one of the earliest deaths from H7N9, developed respiratory illness, one of them dying, but the virus was later ruled out by Chinese authorities.
The WHO confirmed that government finding on Monday.
"The family cluster raises the possibility of human-to-human transmission, but two of the cases in that cluster have not been laboratory confirmed," O'Leary said.
"There is no other evidence pointing toward sustained transmission among people," he added.
Four of the deaths have been in China's commercial hub Shanghai, with the other two in the neighbouring province of Zhejiang.
O'Leary praised China's transparency on the outbreak, following criticism the announcement of the initial deaths was too slow.
"We are very satisfied and pleased with the level of information shared and we believe we have been kept fully updated on the situation," he told the news conference.
The first deaths from the virus were not reported by authorities until three weeks after they occurred. Chinese officials said the delay in announcing the results was because it took time to determine the cause of the illness.
China faced condemnation a decade ago on accusations it covered up the 2003 outbreak of Severe Acute Respiratory Syndrome (SARS), which eventually killed about 800 people globally.