A middle-aged man who transported poultry for a living has died from a new strain of bird flu, the fourth death among 11 confirmed cases in China, the government and state media reported Thursday.

The 48-year-old man, who died in Shanghai, is one of several among the infected believed to have had direct contact with fowl, which may carry the virus. Until recently, the virus, known as H7N9, was not known to infect humans.

It is not known how people are becoming sick with the virus, and health officials and scientists caution that there are no indications it can be transmitted from one person to another. Scientists who have studied the virus's genetic sequence said this week that the virus may have mutated, spreading more easily to other animals and potentially posing a bigger threat to humans.

Guidelines issued Wednesday by the national health agency identify butchers, breeders and sellers of poultry, and those in the meat processing industry as at higher risk.

Experts only identified the first cases on Sunday. Some among the 11 confirmed cases fell ill several weeks ago but only now are being classified as having H7N9.

The government of Shanghai said that in addition to the man's death and two previously confirmed cases, there are three other suspected cases.