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The new strain of bird flu infecting and killing people in China is on the move. All of the reported cases had been contained to a relative few hotspots, but the first reported case of a human infection outside mainland China arrived Wednesday, and that's got the world's top scientists pretty worried about this H7N9 strain—even if it's not being transmitted from person to person.

A 53-year-old man from Taiwan recently returned from a trip to mainland China and showed signs of being infected with the new bird flu virus three days after landing home. (Taiwan is technically part of the larger Republic of China, but also its own country. It's complicated.) He's in critical condition and remains in quarantined at a Taiwanese hospital, where he's been since April 16. "This is the first confirmed H7N9 case in Taiwan who was infected abroad," Taiwan's Health Minister Chiu Wen-ta told reporters.

This is also very concerning because the World Health Organization just finished their own investigation into the H7N9 virus and they're worried it could be even worse than SARS or the H591 bird flu. Remember SARS and the first bird flu? They weren't fun. "This is one of the most lethal influenza viruses we have seen so far," the WHO's assistant director-general for health security, Dr. Keiji Fukuda, said at briefing Wednesday. "This is an unusually dangerous virus for humans," he added.