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To Webster and Shortridge, Hong Kong's many outdoor markets held the key to why the confirmed cases of H5 were spread in such haphazard fashion throughout Hong Kong. In some cases, the CDC team and health-department investigators were unable to prove direct contact with poultry, which suggested that some of the victims caught the virus through contact so casual they simply weren't aware of it. Says Shortridge: "It suggested to me there was a hell of a lot of virus in the environment that we weren't aware of."
Webster and Shortridge quickly arranged an ad hoc task force to begin testing poultry in the city's "wet" markets, so named because retailers use water to clean their stalls and adjacent sidewalks. The group began its probe on Dec. 22 and worked 18 hours a day right through Dec. 28, the day Hong Kong authorities began their territory-wide slaughter. The research showed that 10% of chickens in the markets carried the virus. Ducks and geese in the markets carried it too--especially worrisome, given their ability to carry infections without outward sign of illness. In the markets, all poultry--ducks, geese, chickens--was killed. The slaughter, according to Shortridge and Webster, removed a substantial reservoir of H5 virus from contact with people.
Then suddenly, almost as soon as it started, the second outbreak seemed to be over. The last case occurred on Dec. 28, the day the slaughter began. By late January, Fukuda's whiteboard in Room 58 showed 18 confirmed cases, with six downward arrows.
A killer had come and gone, raising new mysteries even as old mysteries from 1918 were being solved. What allowed this avian virus to cross the species barrier and set up killing infections in man? Why did it strike the young and hardy with the most ferocity--just as the 1918 virus had? And, most important, has the virus really ceased to be a threat, or is it circulating more quietly, primed for a "reassortment event" that will set off the next global disaster?
So far, the new virus has shown no evidence of reassortment. The fact that the outbreak happened in December, before Hong Kong's regular flu season, reduced opportunities for reassortment, as did the prompt slaughter of the chickens. But the flu season is coming. It will peak in late February and early March, with a second peak this summer. What researchers fear most is that someone infected with a common flu strain will also become infected with H5, and thus become an inadvertent mixing chamber for the production of a wholly new virus.
Webster and Shortridge are convinced that the avian virus is still circulating in the environment. "I don't think we're out of the woods yet," says Shortridge. Fukuda agrees: "You would be a fool to predict what the virus is going to do next. I'm equally prepared for this thing to disappear as I am to hear one day when I walk into the office, 'Oh, did you hear? There's another 10 cases--or 100 cases.'"