Health workers pack dead chickens into trash bins at a wholesale poultry market in Hong Kong on Dec. 31. Hong Kong began culling 15,000 chickens and suspended imports of live poultry from mainland China for 21 days after the H7 bird flu strain was discovered in a batch of live chickens that came from the southern province of Guangdong. (Tyrone Siu/Reuters)

A Canadian woman who recently returned from China has become the first North American known to have the H7N9 bird flu, Reuters and the Associated Press are reporting. A man who traveled with the British Columbian woman also is sick and is being tested to determine whether he is infected.

Canadian officials say the risk of transmission of this kind of flu is low. The virus does not appear to travel easily from human to human. But there have been about 500 cases among humans in China and a third of those people have died.

The Centers for Disease Control and Prevention do note that "most concerning about this situation is the pandemic potential of this virus. Influenza viruses constantly change and it’s possible that this virus could gain the ability to spread easily and sustainably among people, triggering a global outbreak of disease (pandemic)."

According to the CDC, the Chinese cases are believed to involve transmission from infected poultry or contaminated environments, because the virus also has been found in poultry. The first case in a human was reported in March 2013.

Symptoms of this type of flu, including pneumonia, can be quite severe. Here's a good Q and A from the World Health Organization on this strain of bird flu.