Wasn't swine flu supposed to be winding down by now?

Well, it isn't. It's spreading faster. And there's a lot more of it around than official health department numbers tell us.

Broward County's official count of confirmed cases is 160. But its chief epidemiologist says the real number could be 20 to 100 times that many.

Miami-Dade's number is 603. The county's chief physician says the real number is much higher, and growing faster than before.

Even more puzzling: Regular flu tends to spread in the winter and wane in the summer. But swine flu shows no signs of slowing down in the United States, where it's summer, or in South America, where it's winter.

What's going on?

For starters, doctors say more than 90 percent of all flulike cases these days are swine flu, with regular seasonal flu nearly dormant. So they are being told not to bother sending most samples to county health departments for confirmation anymore. Broward's chief epidemiologist, Dr. John Livengood, estimates that only 2.5 percent of swine flu cases in his county are being confirmed and counted.

''Not everyone with flu symptoms is tested anymore,'' said Dr. Fermin Leguen, chief physician for the Miami-Dade Health Department.

County health officials investigate swine flu outbreaks mostly when there are a dozen or more cases at a prison or day camp, or if it involves infants or others at high risk, Leguen says.

It's true nationwide. The official swine flu count for the United States is 33,902. But Dr. Anne Schuchat, director of the National Center for Immunization and Respiratory Diseases of the U.S. Centers for Disease Control and Prevention, calls the official number ''just the tip of the iceberg,'' and says the true national count is closer to one million cases.

The good news is that so far the swine flu is relatively mild. Of the 170 deaths in the U.S. so far, three-quarters were people with underlying conditions such as asthma, heart disease and so on. The even better news is that the virus doesn't seem to be mutating into a more virulent strain, making a more serious pandemic this fall and winter a bit less likely.

Why is swine flu growing in both Northern and Southern hemispheres? Dr. Gordon Dickinson, chief of infectious disease at the University of Miami Miller School of Medicine and the Veterans Administration Health System, says it's because of the way flu is spread.

Flu usually grows in the winter, when people in most of the country spend more time indoors, crowded together, he says.

But swine flu is different.

``This is a totally new virus. So even though this is not the ideal time for it to spread, it's able to do so because it can find enough susceptible people who haven't built up immunity from having it before.''

Swine flu is worst among the young, especially those ages 5 to 14, and least contagious to those 60 and older. Dickinson believes it's because older people might have been exposed to flu epidemics in 1950s and 1960s and built up resistance to the virus.

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