China is investigating the possibility of human-to-human transmission of a new strain of bird flu that has killed 17 people and is examining "family clusters" of people infected with the virus, a top health official was quoted as saying.
Authorities have slaughtered thousands of birds and closed some live poultry markets to slow the rate of human infection. But many aspects of this new variety of bird flu remain a mystery, particularly whether the H7N9 strain is being transmitted between people.
China has warned that the number of infections, 82 so far, could rise. Most of the cases and 11 of the deaths have been in the commercial capital Shanghai.
Feng Zijian, the director of the health emergency center at the Chinese Center for Disease Control and Prevention, told reporters on Wednesday that "we are paying close attention to these cases of family clusters.
"(We) are still analyzing in-depth to see which has the greatest possibility -- did it occur first from avian-to-human transmission, and then a human-to-human infection, whether they had a common history of exposure, were exposed to infected objects or whether it was caused by the environment," Feng said.
His comments were reported in a statement posted on the website of the National Health and Family Planning Commission.
One of the families that China is studying is made up of two brothers and their father who died of the virus, Feng said.
"This family cluster case still doesn't change our understanding of the characteristics of the disease in general -- that it is transmitted from birds to people and there's no evidence of human-to-human transmission," Feng said.
Contact with poultry
Efforts to determine the nature of the H7N9 virus are also hampered by a lack of accurate information from the victims on whether they have had contact with poultry, Feng said.
The World Health Organization said on Wednesday that a number of people who have tested positive for the new strain appear to have had no contact with poultry.
The WHO had previously reported two suspected "family clusters", but the first turned out to be a false alarm and the second was inconclusive.
Zeng Guang, chief scientist in charge of epidemiology at the China Disease Prevention and Control Centre (CDPCC), said about 40 percent of human victims had no clear history of poultry exposure, the Beijing News reported.
Feng said that not all patients "can recall the history of exposure. Just like with the H5N1 avian influenza, 50 percent of the patients knew exactly their history of exposure, the other 50 percent can't recall it at all."
He was referring to a an especially virulent strain of bird flu that had raised the threat of a global pandemic in 2003.
Feng said that as most patients were in critical condition, the government was encountering delays in obtaining information about their exposure to poultry.
The WHO said a team of experts going to China soon would examine whether the virus can be spread between people, although there was "no evidence of sustained human-to-human transmission".
The state-run China Daily newspaper, citing an unnamed source, said the team's talks with Chinese representatives would be held on Thursday. The experts would then visit affected areas.