(CNN) — Five more people in China have been infected with a new variation of bird flu, the World Health Organization said Saturday, as it continued to look for the source of the infection.
The five cases bring to 49 the number of people in China who have been infected. Eleven of them died.
WHO also said that a 7-year-old girl from Beijing was infected with the virus. Chinese authorities announced her case earlier in the day.
All of the five new cases are in Shanghai and the surrounding region, where most of the other cases have been located. The new cases 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, the 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.
Wednesday, the Chinese Academy of Sciences said the H7N9 virus probably came from migratory birds from East Asia that mixed with domestic fowl in China's Yangtze River delta region around Shanghai.
H7N9, is normally found in birds. Until last month, it was never known to infect people.
A report in The New England Journal of Medicine this week said the new variation of bird flu has genetic characteristics that make it well-adapted to infect humans.