The 1999-2000 flu season is off and running, with the health
departments in 46 states now reporting outbreaks of influenza. In fifteen
states, and in Puerto Rico, there is a regional (moderate) level of activity,
that is, the outbreaks of flu are occurring in areas holding less than 50
percent of the state's population. At this point, there are three states with
reports of widespread (high) levels of infection, which would affect areas with
more than 50 percent of a state's population. In 30 states, and the District of
Columbia, there are sporadic (low) levels of activity, that is, cases of flu
have been reported but no outbreaks have yet occurred in schools, nursing homes,
or other institutional settings.
Have a look at our interactive flu map of the United States to see how conditions are shaping up in your state, or in a state you'll be visiting. Be aware that the state-by-state influenza data, supplied by the Centers for Disease Control and Prevention, is delayed by a week, so the map is current as of the week ending Dec. 25, 1999.
The annual flu epidemic should peak in February or March. After that, the number of cases will dwindle to practically nothing by the early summer. But in this time, it will have infected between 10 and 20 percent of the U.S. population and killed about 20,000, mostly elderly, Americans, according to the CDC.
Little is known about why flu outbreaks are cyclical, says CDC epidemiologist Carolyn Bridges, M.D. "I don't think people really understand why flu peaks in the winter. Perhaps it's the drier air, maybe it's the crowding indoors," she says.
Once you've been exposed to a particular strain of flu virus, either through vaccination or infection, your body develops resistance to it. But the wily flu virus is constantly changing its coat in an attempt to stay one step ahead of the watchful human immune system. This is why virus sleuths at the CDC and other worldwide health agencies are constantly scouring the planet for the latest versions of the flu virus. The CDC analyzes samples of suspected influenza virus from across the country and around the world. Additionally, it receives weekly reports from state health agencies and from a network of 260 doctors who report the number of those patients with influenza-like illness by age group. The CDC uses the information to develop effective vaccines and to get early warning of an epidemic of deadly flu.
Virus tracking paid off in December 1997, when an outbreak of a particularly deadly strain of flu jumped from wild birds to domestic poultry and finally to humans. Of the 18 people infected, six died, a whopping 33 percent mortality rate. Thanks to quick action on the part of Hong Kong health officials, who ordered the wholesale slaughter and incineration of chickens, a worldwide pandemic may have been averted, and as far as anyone can tell, the strain of influenza, known as type A (H5N1) has been eradicated from the human population.