China Scrambles to Track Mystery Bird Flu New outbreaks as officials fear H7N9 may have mutated By Evann Gastaldo, Newser Staff Posted Apr 3, 2013 7:19 AM CDT Updated Apr 3, 2013 7:33 AM CDT 3 comments Comments A woman with a mask shops at a poultry market in Beijing, China, Thursday, Jan. 8, 2009. (AP Photo/Andy Wong) (Newser) – Four more people in coastal China are hospitalized with the new H7N9 strain of bird flu, China announced yesterday. H7N9 has already killed two people and left a third in critical condition; the four new patients, aged 32 to 83, are also critically ill, the New York Times reports. Chinese officials had previously thought humans weren't susceptible to H7N9, and they still maintain that human-to-human transmissions haven't occurred. Notably, one new victim is a poultry butcher. There is no vaccine for H7N9, and the AP reports that it also may be more difficult to track than H5N1, which killed hundreds in Asia starting a decade ago. Scientists say H7N9 may be able to spread among poultry undetected, causing no symptoms in the birds but making humans very ill. The virus also appears to have mutated, meaning it could infect other animals—including pigs, though Beijing emphasized Monday that there was no link to the 15,000 dead pigs in a Shanghai river. Scientists are calling for widespread animal testing in the region.