Chinese researchers have reportedly confirmed poultry as a source of H7N9 flu among humans but say they found no evidence of person-to-person transmission.

A probe into four cases of human H7N9 influenza in eastern Zhejiang province has determined all the patients were exposed to poultry, either by working or visiting wet poultry markets, also known live poultry markets.

The World Health Organization had previously said poultry were the likely source of the virus, which has been linked to at least 22 deaths out of 108 identified cases since February 2013.

A team led by Lanjuan Li of Zhejiang University in Hangzhou and Kwok-Yung Yuen of the University of Hong Kong took rectal swabs from 20 chickens, four quails, five pigeons, and 57 ducks all from six live poultry markets likely to thave been visited by the patients. Their findings have been reported in the general medical journal, The Lancet. Two of the pigeons and four of the chickens tested positive for H7N9 but the virus was not found in any of the ducks or quails.

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The researchers analyzed the genetic makeup of H7N9 found in one of the patients and compared it to a sample found in one of the infected chickens. The similarities "suggest that it is being transmitted sporadically from poultry to humans," according to The Lancet. "This is the first time that definite bird-to-human transmission has been shown for the H7N9 virus."

Doctors also monitored 303 other people who were relatives or coworkers of the patients, as well as 82 health care workers. "Nobody else who came into contact with the H7N9-infected patients began to show any symptoms within 14 days from the beginning of surveillance, suggesting that the virus is not currently able to transmit between human beings," the journal said.

However, further adaptation of the virus could lead to infections with less severe symptoms and "more efficient person-to-person transmission," the researchers cautioned.