A strain of bird flu that has been found in humans for the first time in eastern China is no cause for panic, the World Health Organization said on Monday, as the number of people infected rose to 24, with seven deaths.
WHO praised China for mobilising resources nationwide to combat the H7N9 flu strain by culling tens of thousands of birds and monitoring hundreds of people close to those infected.
"So far, we really only have sporadic cases of a rare disease, and perhaps it will remain that way. So this is not a time for over-reaction or panic," said WHO representative Michael O'Leary.
The head of China's National Health and Family Planning Commission, Li Bin, said on Sunday she was confident authorities could contain the virus.
"These are a relatively small number of serious cases with personal health, medical implications, but not at this stage known public health implications," O'Leary told reporters.
But he warned that information on the virus was still incomplete.
"We really can't rely on information from other viruses. H7N9 is a new virus in humans and the pattern that it follows cannot be predicted by the patterns that we have from other influenza viruses," O'Leary said.
No cases have yet been reported outside of China, he said.
The Shanghai government said on its official microblog on Monday that a 64-year-old man had become the latest victim as the number of infected has risen daily.
In total, 621 close contacts of the people known to have been infected were being monitored and had yet to show symptoms of infection, the director of China's H7N9 prevention and control office, Liang Wannian, said.
Authorities have said there is no evidence of transmission between humans.
The bird flu outbreak has caused global concern and some Chinese internet users and newspapers have questioned why it took so long for the government to announce the new cases, especially as two of the victims fell ill in February.
Airline shares have fallen in Europe and in Hong Kong over fears that the new virus could be lead to an epidemic like Severe Acute Respiratory Syndrome (SARS), which emerged in China in 2002 and killed about 10 percent of the 8,000 people it infected worldwide.
Chinese authorities initially tried to cover up the SARS outbreak.
In the H7N9 case, it had said it needed time to identify the virus, with cases spread between eastern Zhejiang, Jiangsu, and Anhui provinces.
Chinese authorities have countered speculation that the H7N9 outbreak is related to more than 16,000 pig carcasses found dumped in rivers around Shanghai and the WHO has said some dead pigs from the rivers tested negative for influenza infection.
Other strains of bird flu, such as H5N1, have been circulating for many years and can be transmitted from bird to bird, and bird to human, but not generally from human to human.
Bangladesh on Monday reported its first H5N1 death, that of a baby, in February. It had taken that long to identify the strain.