There has also been occasional human-to-human transmission, according to the World Health Organization.
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But the WHO says there is currently no evidence of human-to-human transmission of the virus.
The World Health Organisation (WHO) said there was no evidence yet of human-to-human transmission.
"We continue to see human-to-human transmission, community transmission, primarily in North America, " said WHO Assistant Director-General Keiji Fukuda.
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In a statement, the WHO reiterated that there was not yet any evidence of human-to-human transmission of the virus.
So far, the WHO said, there is no evidence of ongoing human-to-human transmission.
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Previous cases of human-to-human transmission may have occurred in Hong Kong, Vietnam and Thailand, as well as in Indonesia.
Authorities have yet to find any connection between the cases and say there is so far no evidence of human-to-human transmission.
This comes after the French health ministry confirmed a second man had contracted the virus in a possible case of human-to-human transmission.
It is also not yet known how all the infections occurred, with the WHO unable to confirm any cases of human-to-human transmission.
It is not yet known how people are catching the disease, although the WHO says there is currently no evidence of human-to-human transmission.
Health authorities are testing a family infected by H7N9 in Shanghai for human-to-human transmission of the new bird flu strain, The Beijing News reports.
But the WHO says there is no evidence of human-to-human transmission.
The WHO said investigations were being conducted into the likely source of the infection, the method of exposure, and the possibility of human-to-human transmission of the virus.
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We have yet to see human-to-human transmission of the virus.
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Officials are reminding the public to remain calm and say there is still no evidence of human-to-human transmission or links with recent discoveries of dead pigs, the newspaper adds.
To better understand the virus's spread and potential for human-to-human transmission, Chinese and World Health Organization officials said Wednesday in Beijing that they plan to boost surveillance and research on H7N9.
Chinese and World Health Organization officials said Wednesday in Beijing that they plan to boost surveillance and research on the H7N9 virus to understand its spread and potential for human-to-human transmission.
Turning to China's bird flu outbreak, the government says there is still no evidence of human-to-human transmission of the H7N9 virus but does not rule out a further spread of outbreaks.
However, it warns that two clusters in Saudi Arabia and Jordan, "raise the possibility of limited human-to-human transmission" or they could have been exposed to the same source of the infection.
The move means the U.N. agency has determined that the virus is capable of significant human-to-human transmission -- a major step toward a pandemic, but not necessarily inevitable, Dr. Keiji Fukuda said.
Amid growing public concern over the outbreak, health authorities have promised transparency and stressed that there is no evidence of human-to-human transmission of the new strain of deadly bird flu, China Daily reports.
Since neither of the two children, a 10-year-old boy and a 9-year-old girl, had contact with pigs, it "increases the possibility that human-to-human transmission of this new influenza virus has occurred, " according to a CDC report.
The move from level three to level four on the WHO's six-level threat scale means the world body has determined the virus is capable of significant human-to-human transmission -- a major step toward a flu pandemic, said Dr. Keiji Fukuda, the agency's assistant director-general.
In other domestic news, the World Health Organization is watching out for mutations and possible human-to-human transmission of the new H7N9 bird flu strain after two family cluster cases - a father-and-son cluster and a husband-and-wife cluster - were detected in Shanghai, China Daily reports.
But in the current issue of The New England Journal of Medicine, Thai doctors report two cases of apparent human-to human transmission of the bird flu.
An increasing focus among public health officials and the media is the prospect that transmission of the disease is not only animal-to-animal but also human-to-human.
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