Dr. Wenqing Zhang, head of the WHO's global influenza program, said Thursday the organization wants to get the big picture of the case.
Zhang told CBC News from Geneva that two main questions need to be answered about the woman's death in Alberta:- Where did she visit?
- How did the exposure happen?
A second focus for the WHO is on close contacts, Zhang said. The goal is to understand whether any human-to-human transmission occurred.
Dr. Michael Gardam, an infectious disease consultant with Toronto's University Health Network who's not with the WHO, says it's "odd" for humans to get infected with H5N1 from a non-poultry source.
"Almost all of the cases that we've heard about going back to the 1990s, there's been direct contact with poultry," said Gardam. "So if this person hasn't visited farms and hasn't been around birds, that's very odd. I imagine they'll be doing a lot of sleuthing in China to figure out what happened."
There's no evidence H5N1 can spread easily between people. When it has, there has been sustained contact, such as between patients and family members, or patients and health-care workers.
The window for any further transmission between people is closing, since normally people would get sick with symptoms two to eight days after exposure to the virus, Zhang said. The woman first showed symptoms of the flu on a Dec. 27 flight.
The investigation involves interviewing people in Beijing and retracing their steps, said CBC health commentator and physician assistant Maureen Taylor.
"If they can't find a bird source, then what's going on with this virus?" Taylor asked. "There were companions of this victim on the plane. Were they with them in Beijing? What was brought into the home as far as eating? Were there birds brought in?"
The H5N1 virus is on WHO's radar as its experts look for any potential signs its gaining the ability to spread rapidly between people.
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