China has found two more cases of a new strain of bird flu and one of the victims has died, state media said on Wednesday, bringing to nine the number of confirmed human infections from the previously unknown flu type.
A 38-year-old cook fell ill early last month while working in the province of Jiangsu, where five of the other cases were found. He died in hospital in Hangzhou city on March 27, the Xinhua news agency reported. Samples tested positive on Wednesday for the new bird flu strain, H7N9.
The second patient, also in Hangzhou, is a 67-year-old who is having treatment. Xinhua said no connection between the two cases had been discovered, and no one in close contact with either patient had developed any flu-like symptoms.
The World Health Organization said it was "following the event closely" and was in contact with Chinese authorities, which it said were actively investigating the cases amid heightened disease surveillance.
Flu experts across the world are studying samples isolated from the patients to assess H7N9'S human pandemic potential.
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.
So far, this lack of human-to-human transmission also appears to be a feature of the H7N9 strain.
Of the seven other cases of the new strain, two have died, both in the business hub of Shanghai. The other five are in a critical condition in hospital in Nanjing. Shanghai, Nanjing and Hangzhou are all close to each other in eastern China.
China's Agriculture Ministry said it had yet to find any animals infected with H7N9, though added it was possible it had been brought to China by migratory birds.
The WHO says so far it has seen no evidence of human-to-human transmission, but there are questions about the source of the infection and about how it may be being transmitted to people.
"We still don't know the mode of transmission or host (of the virus)," said WHO spokesman Gregory Hartl. "Those are the two most important pieces of information we would need. In order to control it, we need to know where it is coming from."
The WHO said in a statement it was also focusing its efforts on encouraging collaboration between researchers to ensure information and materials are available for scientists wanting to develop diagnostic tests, drugs and vaccines.
No vaccine is currently available for H7N9 flu, but preliminary test results provided by the WHO Collaborating Centre in China suggest it is susceptible to the antiviral drugs Tamiflu, sold by the Swiss drugmaker Roche, and Relenza, sold by Britain's GlaxoSmithKline.
Chinese authorities dismissed speculation on some websites that the H7N9 outbreak may be related to more than 16,000 pig carcasses found dumped in rivers around Shanghai.
Yin Ou, deputy director of the Shanghai Municipal Agricultural Committee, told reporters on Tuesday that the city had tested 34 dead pigs found in the city's Huangpu River for the H7N9 virus, but the tests had all come back negative.
China has a chequered record when it comes to tackling disease outbreaks, which some officials have previously sought to cover up. However, since the H7N9 cases have been identified, China has stepped up its alert level and said it is being transparent in dealing with them.
In 2003, authorities initially tried to cover up an epidemic of Severe Acute Respiratory Syndrome, which emerged in China and killed about a 10th of the 8,000 people it infected worldwide.