The 2003-04 flu season came on like an early winter storm, jamming emergency rooms and fueling a run on flu vaccine.
And just as quickly, it seems to be over.
Every state but Alabama reported some cases of flu as of Jan. 31, but no states report it as widespread, says the Centers for Disease Control and Prevention.
That's a drastic change from mid-December, when the CDC's U.S. flu map was awash in red, showing flu was widespread in 45 states. Now the map is not nearly as alarming, with states reporting flu cases or outbreaks here and there.
The CDC says it has been notified of 129 flu-related deaths in people under age 18, including 78 in children under 5. Because states are not required to report flu deaths in children, it's not known how this compares with previous years, although a mathematical model has estimated 92 deaths per year in children under 5.
Because of widespread reports of serious illnesses and deaths in children early in the flu season, the CDC requested states to track them this year and will request the Council of State and Territorial Epidemiologists to make reporting of flu deaths in children a standard practice.
The annual flu season normally runs from November through March, but it got going last October in Texas, weeks ahead of schedule, and began to spread. By mid-November, Colorado was reporting record numbers of cases, and soon after, flu seemed to hit everywhere at once, says Stephen Ostroff, deputy director of the CDC's National Center for Infectious Diseases.
''This was a flu season with a very sharp up-slope that peaked rapidly and started going down quickly,'' Ostroff said. ''It looks like all different parts of the country got hit within a couple of weeks of each other. Then it just disappeared over a period of two to three weeks.''
That's not uncommon during years when the strain of flu that predominated this season, type A/H3N2, is circulating, he says. ''We have seen that pattern in other H3N2 years,'' he says. ''It comes on like gangbusters, then burns out pretty quick.''
But flu is tricky, he says. There's no evidence of a late-season comeback, but ''it wouldn't be unprecedented,'' he says.
It's not clear yet if the flu caused more illness and death than in an average year, when 10% to 20% of the population gets sick, 36,000 people die and 114,000 are hospitalized because of flu and its complications. CDC continues to report flu data through May.
But in some parts of the country, it was clearly a very bad flu season. Hospitals in several Western states were overflowing, and schools closed early for the holidays because of high absenteeism.
In Colorado alone, 12,247 confirmed cases of flu have been counted, up from 2,681 during the 2002-03 season.
Raised awareness may have encouraged wider use of flu vaccine. Even though the vaccine was not a perfect match for the strain of flu in circulation, most doctors believe it may have prevented severe cases.
The publicity about the severity of the flu season ''made people realize how serious flu can be and how important flu vaccine is for them and their children,'' says Cindy Parmenter of the Colorado Department of Public Health and Environment. ''Many people think they don't need a flu shot unless they're elderly.''
Len Lavenda of Aventis, which manufactures the bulk of the U.S. flu vaccine supply, says the company was sold out of vaccine in early December, something that had never happened before. ''Normally, we end up the season with millions of unsold doses,'' he says.
Orders are now being placed for next fall's vaccine supply, though the company has not yet decided how much it will produce.
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