China's Health Ministry announced Saturday that the 19-year-old soldier who was hospitalized May 14 with a fever and a cough had contracted the H5N1 bird flu.
The announcement did not further identify the soldier or how he might have contracted the disease - questions the WHO said it was pressing the Health Ministry to answer.
Joanna Brent, the WHO's spokeswoman in Beijing, said the ministry told the health body Monday that the soldier was stationed in the southern province of Fujian but did not have any more details.
"One individual H5N1 case is not in itself cause for alarm but its occurrence shows that the virus is still circulating and a continuing public health threat," Brent said.
According to her, the ministry also said Monday people who had close contact with the soldier were under medical observation but showed no signs of disease.
"Again there's been a human case without a poultry outbreak warning and so there needs to be strengthened surveillance," Brent said.
China's two other reported human cases of bird flu this year were a farmer in Fujian and a 16-year-old boy who died in March in the eastern province of Anhui - the country's 15th fatality from the disease.
International experts have repeatedly complained about Chinese reticence in cooperating on investigating emerging diseases like bird flu and pneumonia from SARS, or secure acute respiratory syndrome.
Additionally, the military, a power unto itself in China, and is usually secretive about its operations. Last year, it was disclosed that new tests on the body of a 24-year-old soldier who died in 2003 in Beijing confirmed that he succumbed to bird flu.
The military also has not provided a promised virus sample from that case, the WHO has said.
Two other specimens from recent human cases in China arrived in the United States last week from the Health Ministry after a lag of about a year.
While the WHO does not mandate sharing virus samples, they are needed to produce diagnostic tools and vaccines. The lack of cooperation, experts say, could slow efforts to track diseases and develop vaccines and other strategies to deal with them.
Bird flu has killed at least 186 people since H5N1 started ravaging poultry flocks in late 2003.
Experts have warned that if outbreaks in birds are not controlled, the virus may mutate into a form more easily passed between people, potentially resulting in millions of deaths worldwide.