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.

Despite those troubling words, the WHO said it's too soon to conclude that the H7N9 virus has been transmitted through human-to-human contact. Of the 108 infected and 22 killed in China since the virus emerged in March, the source has been traced to open poultry markets. WHO scientists believe the virus could be transmitted from birds to humans much easier than the H5N1 virus. Last week, China was worried recently about the disease spreading from human to human, but the WHO has shot that idea down, at least for now. "Evidence so far is not sufficient to conclude there is person-to-person transmission. Moreover, no sustained person-to-person transmission has been found," Fukuda said Wednesday. Still, some experts believe limited human-to-human transmission may have occurred.

Things were looking up for a few minutes, though: Infections seemed to drop after the Chinese government ordered the open poultry markets be closed until they can figure out what's going on with this latest bird flu virus. (Fukuda admitted they don't know much about the virus yet.) 

That the infected Taiwanese man says he never came in contact with any poultry while traveling in China, then, might be cause for concern. "To our best knowledge, the man has come in contact with 139 people and so far none has exhibited any symptoms of the virus," Chang Feng-yee, the director general at Taiwan's Center for Disease Control, said Wednesday.