Posted on behalf of David Cyranoski:

Two men died after being infected with a type of bird flu never before been seen in humans, China reported on March 31. The two Shanghai men, 87 and 27 years old, contracted the H7N9 virus in February and died within 8 days. A 35-year-old woman from Anhui province, who contracted it in March, is now in critical condition.

The path of transmission of the three cases is not clear. The younger woman reportedly had contact with birds, and the 27-year-old man and younger woman were both butchers. After examining 88 close contacts with the infected, China’s CDC has concluded that the virus is not passing between humans.

But two sons of one of those confirmed to have an H7N9 infection also suffered acute pneumonia, and one died. The cause is yet unknown, but health authorities are calling the cluster of severe pneumonia worrisome.

Another case — of a 45-year-old woman in Jiangsu, which lies between Anhui and Shanghai, has been reported but not yet confirmed.

Nature will post more on the news later today.