Scientists in China have confirmed for the first time that the influenza A H7N9 (bird flu) virus has been transmitted from birds to humans.

However, there is still no evidence that the virus can transmit among humans.

According to a report in the Lancet journal the bug was transmitted from chicken at a wet poultry market-to humans.

Since it emerged in February of this year, 108 people are believed to have been infected with the H7N9 flu virus, which has now appeared in several different regions of China, and is believed to have killed 22 people.

Previous reports centred on cases in the Shanghai region, but  the new report details four confirmed cases of human H7N9 infection in another part of China, the Zhejiang province south of Shanghai.

All four of the patients had been exposed to poultry, either through their occupation or through visiting poultry markets. The researchers tested 20 chickens, four quails, five pigeons, and 57 ducks, all from markets likely to have been visited by the patients. "

"Two out of five pigeons (40%), and four out of 20 chickens (20%) tested positive for H7N9, but the virus was not found in any of the ducks or quails tested," according to the report.

"After analysing the genetic makeup of H7N9 virus isolated from one of the patients, and comparing it to an H7N9 virus isolate taken from one of the wet market chickens, the researchers conclude that similarities between the virus isolates suggest that it is being transmitted sporadically from poultry to human beings," the report added.

This is the first time that confirmed bird to human transmission has been shown for this potentially deadly flu virus.

Surveillance of 303 of the patients' household and workplace contacts, as well as 82 health care workers who came into unprotected contact with any of the patients, revealed that nobody else who came into contact with the flu-infected patients showed any symptoms , suggesting that the virus is not currently able to transmit between humans.

"However, genetic analysis has shown that the virus has acquired some characteristics which adapt it specifically to infection in mammals, and the authors caution that further adaptation of the virus could lead to infections with less severe symptoms and more efficient person-to-person transmission," according to the Lancet report.