(CNN) -- China has two new cases of humans infected with bird flu, bringing the total to 51, state media reported Sunday.
The patients in Henan province tested positive for the H7N9 virus, according to Xinhua news agency.
The virus is normally found in birds and was never known to infect people until last month.
A day before the announcement, the World Health Organization said China had been infected with a new variation of bird flu. The agency said it continued to look for the source of the infection.
Of the total cases, at least 11 people have died.
On Saturday, the world body announced five new cases in Shanghai and the surrounding region, where most of the infections have been located. Those new patients range in age from 38 to 77, WHO said.
"Investigations into the possible sources of infection and reservoirs of the virus are ongoing," the organization announced. "Until the source of infection has been identified, it is expected that there will be further cases of human infection with the virus in China."
So far, WHO said, there is no evidence of ongoing human-to-human transmission.
A possible source for the infections is poultry markets, which have become the focus of investigation by China's health ministry and WHO.
Several cities in eastern China have suspended trading in live poultry in an effort to contain the problem.
Chinese scientists said the H7N9 virus probably came from migratory birds from East Asia that mixed with domestic fowl around Shanghai.
The new variation of bird flu has genetic characteristics that make it well-adapted to infect humans, the New England Journal of Medicine said.