There have been a handful of family clusters, but WHO says no sustained human-to-human transmission has occurred. However, scientists warn that the H7N9 virus contains genetic markers that could help it infect mammals easier than other avian flus. Infected birds also do not show symptoms, making it harder to track the disease. Cases declined in China over the summer, which is typically slower for influenza viruses, after some local live poultry markets were temporarily closed.
In Hong Kong, which has logged three cases, officials will test all poultry for the virus beginning later this week. Taiwan has reported two cases.
In past years, it was the H5N1 bird flu virus that spiked during this time of year. That strain, which has killed at least 386 people since 2003, is still circulating widely in poultry stocks and kills about 60 percent of the people it infects.
On Tuesday, Vietnam, which has long battled the virus, confirmed its first H5N1 death in nine months. Earlier in January, the first human case was reported in North America after a person traveling back from a trip to Beijing became ill and died in Canada.
Both bird flus cause high fever and respiratory problems, including pneumonia and shortness of breath. Scientists have repeatedly warned that the viruses cannot be ignored because of their potential to possibly spark a global pandemic. But after years of campaigning in countries where it's common for chickens and pigs to live closely with people, sometimes in the same house, that message is often a hard sell.
"After almost a decade of sitting on the proverbial edge of the H5N1 pandemic cliff and not falling off, people are beginning to think that we never will fall," Michael Osterholm, an infectious disease expert at the University of Minnesota, said by email. "But the best scientific assessment of microbial genetics tells us we could still fall off of that cliff and if we do, the global consequences could be devastating."
Poultry is a central part of many families' dinner tables during the Lunar New Year festivities, and it's often bought live and killed at home in China and elsewhere across the region. The WHO urges care when slaughtering and preparing birds, including frequent hand washing. However, well-cooked meat and eggs do not pose a threat.