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Technicians carry out a test for the H7N9 bird flu virus using test reagents at the Beijing Center for Diseases Control and Prevention in April 2013.Reuters

The Public Health Agency of Canada has confirmed North America's first human case of H7N9 influenza, a strain of avian flu that can cause severe pneumonia and death but is not believed to spread easily from person to person.

A British Columbia couple in their 50s fell ill with the "classic" influenza symptoms of a fever and cough shortly after returning to the province's lower mainland on Jan. 12 from a trip to China.

On Monday morning, tests confirmed the woman has H7N9. The man, who is also sick, is suspected of having the same strain of the virus, but that has not yet been confirmed.

The couple have isolated themselves at home and are already recovering, public-health officials said Monday at a news conference announcing the case. The couple's contacts are being monitored for symptoms, but none have fallen ill so far.

"I want to emphasize that the risk to Canadians is very low because there is no evidence of sustained human transmission of H7N9," said Gregory Taylor, Canada's chief public health officer. "This particular strain of H7N9 has not been found in wild or domestic birds in Canada. The virus H7N9 is not like H5N1 avian influenza. H5N1 transmits much more easily between birds and people and those infected usually have more severe illness."

H7N9, a subtype of influenza that had been found in birds in the past, was first discovered in humans in China in March, 2013. Since then, about 500 human cases of the strain have been documented in China. The strain has caused concern in that country because it tends to lead to symptoms more serious than those caused by typical influenza, including severe pneumonia.

In its most recent formal assessment of the risk posed by H7N9, published last October, the World Health Organization found 453 laboratory-confirmed cases of the strain and 175 deaths.

In the case of the British Columbia couple, public-health officials are not certain precisely where or how they contracted the virus. They did not visit any Chinese farms or live poultry markets, which are common places for H7N9 to make the leap from birds to humans. They were part of an organized tour for part of their trip, but travelled on their own, as well.

"They did some touring of areas and villages in China where poultry are seen throughout the village, but there was not a particularly high-risk exposure that we were able to identify," said Bonnie Henry, British Columbia's deputy provincial health officer.

The couple flew home on Air Canada Flight 8 from Hong Kong to Vancouver, landing Jan. 12.

However, neither was showing symptoms on the plane, so public-health officials believe it is highly unlikely they transmitted the virus to others on the flight. Doctors believe both contracted the virus directly from a bird while in China; they do not think one member of the couple passed it to the other.

A few days after returning from their vacation, the man began to experience flu-like symptoms. The next day, the woman fell ill, too. She visited her family doctor, who took a swab that was sent on for testing, first at a provincial laboratory in British Columbia and then at the National Microbiology Laboratory in Winnipeg.

Both were treated with antiviral medication and neither needed to be admitted to hospital.