As the number of cases of a deadly strain of bird flu rises in China, health officials there are investigating the possibility that the disease has spread from human to human.
World Health Organization spokesman Gregory Hartl cautioned Thursday that there was no conclusive evidence that the new virus, known as H7N9, has been transmitted between people, but said investigators have homed in on three families in Shanghai and two young children in Beijing as possible examples of human-to-human transmission.
The development followed comments a day earlier by a Chinese expert on the disease who said about 40 per cent of people infected with the virus claimed not to have had contact with poultry, which has been suspected to be the primary source of infections. The expert, Feng Zijian, director of the health emergency centre at the Chinese Centre for Disease Control and Prevention, also played down the possibility of "effective" transmission between people.
The virus has infected 87 people, including 17 who died, since China informed the World Health Organization last month of the outbreak, according to China's state-run news agency, Xinhua.
Twenty-four of those cases were discovered in the past two days.
Andrew Simor, an infectious diseases expert at Sunnybrook Health Sciences Centre in Toronto, said the development was not cause for immediate concern but that it was something that needed to be closely watched by the international health community.
"As soon as there is person-to-person transmission, that changes the game entirely because now you've got a substantial risk, much like the seasonal flu," Dr. Simor said. "Having said that, it depends on the degree of transmissability."
"A pandemic requires efficient human-to-human transmission, and that certainly hasn't been documented yet," Dr. Simor added.
The H1N1 virus was a strain that sparked a worldwide pandemic in 2009 and 2010.
Infections in the latest outbreak have popped up across China, but the majority of cases and fatalities have been concentrated in Shanghai.