International flu experts will head to China in the next few days to help investigate the outbreak of H7N9 bird flu, the World Health Organization says.

Another eight people are infected with the virus, which is tied to 14 deaths in 71 confirmed cases, state news agency Xinhua said. The new cases were in the eastern provinces of Jiangsu and Zhejiang.

"We're still trying to find out more information about the reservoir [of the virus]," WHO spokesman Glenn Thomas told reporters at a regular United Nations news briefing in Geneva. "From what we know at the moment, the poultry markets have been a focus of attention, but the fact-finding mission will be looking into this as a key target of its research."

Nurses collect blood samples from patients at a specialized fever clinic at Beijing's Ditan Hospital. (Andy Wong/Associated Press)

Scientists want to know what the animal source is to try to gain clues about how people became infected.

The specialists are experts in fields such as emerging viruses and epidemiology.

A four-year-old boy in Beijing confirmed as an H7N9 flu virus carrier is to be discharged from hospital, China Central Television said today. He'd been placed under observation to see if he developed symptoms.

Beijing Health Bureau deputy director Zhong Dongpo said the boy's case illustrates a range in how the infection manifests, from not showing any abnormalities to slight cases and critical symptoms.

The diversity of symptoms adds to the complexity of determining the true number of infections in humans and birds.

The eight-member investigative team includes four non-WHO staff, said Gregory Haartl, the agency's director of communications.

The H7N9 strain was not previously known to infect humans. Doctors and scientists closely watch for any sign that the virus is jumping from person to person to person as part of their pandemic risk assessments.