The first major test of the center came after SARS, the deadly respiratory disease, was first detected in China last November.
The Centers for Disease Control and Prevention was preparing to post new information on its Web site for health workers, detailing how to properly prioritize patients who show up at hospitals with possible flu symptoms.
The flu season has struck early, and many areas have reported flu shot shortages as demand quickly outpaced supply. But the government has worked to purchase remaining flu shot supplies for states.
During the SARS outbreak, the CDC was able to distribute more than 2.5 million alerts to incoming travelers on more than 300,000 direct and 2 million indirect flights to the United States. It also broadcast the latest information to China about the disease, which killed 774 people and sickened more than 8,000.
The government said Thursday that flu is now widespread in 36 states - almost everywhere except the upper Midwest and a few Eastern states.
How many will die when it is over? Probably tens of thousands. Beyond that, exact numbers are hard to pin down.
The reason: Most people who catch the flu never go to a doctor. And even if they do, they usually never get a definite diagnosis.
The flu is difficult to distinguish from other winter viruses. In most cases, there is little reason for doctors to go to the trouble of identifying the culprit, which traditionally has required growing the virus in a culture, a process that takes two weeks.
Even if they do, chances are good they will find nothing.
By the time people are sick enough to go to the hospital, they may be suffering from flu's aftereffects, such as bad bacterial infections, not the flu virus itself. It's already been defeated and expelled from the body. Certainly by the time someone dies of the flu, all traces of it have long since disappeared.
So unlike many less common illnesses, such as botulism, plague and rabies, state health departments are not required to send reports of flu cases or deaths to the Centers For Disease Control and Prevention.
Spokesman David Daigle said the CDC has been working with the Council of State and Territorial Epidemiologists for the last three or four weeks to gather information on pediatric deaths.
Several states have sent in reports and specimens, giving the CDC a total of about three dozen deaths among children and teenagers. Daigle said the agency is considering a formal request to all states to cooperate.
For now, the best estimate of flu's toll must wait until the season is over. Using computer analyses, CDC researchers calculate how many people died both during the flu season and when flu viruses were not circulating.
The difference, they say, is a rough idea of how many died of the flu that season. Since flu rarely shows up on a death certificate, they narrow the number down by focusing on deaths in a broad category of respiratory and circulatory ills that could result from the infection.
This way, they figure the total number of U.S. flu deaths in an average season is 36,155. However, 90 percent of these deaths are in people over age 65. The estimated number in those under age 5 - 92 - is based on so few cases that it could be way off in any year.
"When you say 92, it gives an image of real precision, but in fact it's a ballpark estimate," said Dr. Keiji Fukuda, the CDC's top flu epidemiologist.
The lack of certainty made it especially difficult to judge whether the childhood flu deaths reported to the CDC this season are unusually great for this point in the season.
"One thing we will be doing this year is trying to figure out specifically how bad a year this is for kids by counting the number of confirmed flu deaths," Fukuda said.
New, rapid flu tests that are taking the place of traditional cell cultures may eventually help make the disease easier to track. These tests, done in the doctors office, take about 15 minutes.
For now, they are typically used only when patients seek care soon after their symptoms start. If given quickly enough, the medicines can ease the disease, so doctors use the test to make sure flu is truly the cause.
In its weekly bulletin, the CDC said the flu is now widespread in Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Georgia, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Massachusetts, Mississippi, Missouri, Montana, Nebraska, Nevada, New Mexico, New York, North Carolina, North Dakota, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Carolina, Tennessee, Texas, Utah, Vermont, Virginia, Washington, West Virginia and Wyoming. All the rest have at least some flu.