This flu season already seems to be a bad one. According to Dr. Sanjay Gupta, and mathematical methods and Google Flu, New York City may be hit with a flood of flu-stricken residents the week of January 10th .

At Nazareth Academy, a Catholic high school just outside Chicago, a full quarter of the 780 students were out with the flu in early December, along with more than a dozen teachers. Officials at the school closed it for two days and disinfected the property.

The principal, Deborah Tracy, said it was the first time in her 15 years there that such a measure had been necessary. “It just really was unprecedented for here,” she said.

Nationwide, we’re on track for a nasty flu season, with both a large number of cases and many severe ones that require hospitalizations, according to the Centers for Disease Control and Prevention. It declared an influenza epidemic this week, a status achieved at some point nearly every year, though not usually this early in the season. Twenty-two states and Puerto Rico are reporting high flu intensity. In some parts of the country, flu infections have outpaced those from each of the last few years, according to data from the C.D.C.

Google Flu Trends, which measures flu intensity using search terms, shows a similar pattern of high flu activity.

The worrisome outlook is the result of a confluence of factors: an early start to the flu season, with more people sick in December than usual; a strain that tends to make people sicker; a relatively low vaccination rate; and a mismatch between this year’s flu vaccine and the virus that’s making people sick.

“We’re already above the peak that we saw last year, and we’re increasing,” said Dr. Michael Jhung, a medical officer at the Influenza Division of the C.D.C. who predicts it will be several more weeks before flu infections peak.

The C.D.C. tracks flu deaths, hospitalizations and the percentage of doctors’ visits for flulike illness. The detailed, public data make it easy to watch the flu take off this year.

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Jeffrey R. Ungvary President