Doctors have pieces, but disease still puzzles.

Byline: Ronald Kotulak, Peter Gorner and Robert Becker

ROCHESTER, Minn. _ The air they breathe is clean, their neighborhoods are safe, their schools are top-notch and their medical needs are taken care of by the Mayo Clinic or the Olmsted Medical Center.

So why do the children in this town on the Minnesota prairie have nearly the same asthma rates as children living in poverty in Chicago?

Asthma as a diagnosed disease has just about doubled in the United States in the last three decades for still unknown reasons, its fury focused on inner-city children, researchers thought, because they live in impoverished, polluted conditions.

But scientists are now discovering that asthma is a disease blind to socioeconomic, ethnic or racial boundaries _ findings that deepened the mystery of a previously uncommon illness that marched into the second half of the 20th century like a breath-robbing army.

Researchers know genes play a role, but they don't know which ones; they know lifestyle and environment can be factors, but they can't quantify to what degree.

And while doctors now have better drugs to fight the disease, they don't have any that prevent or cure it, and they don't even know why the medications work.

In fact, doctors still can't agree on what exactly defines asthma.

"To me, we're much farther behind today than I thought we'd be in 1995," said Dr. Jeffrey Drazen, a leading asthma researcher at Harvard and editor-in-chief of the New England Journal of Medicine.

Drazen said researchers in the mid-1990s thought a cure was in sight, but the trials of promising new medications failed. "We all predicted that by `01 we'd really know a lot more. The fact that all the drugs bombed really set us back," Drazen said.

In the U.S., about 15 million people have asthma, an estimate considered low by some experts. It has become the No. 1 chronic disease of children. It is the primary reason that kids across the country are hospitalized and one of the top reasons they miss school and curtail physical activity.

It is a disease that maintains Chicago and Illinois firmly in its grip. While asthma mortality has dropped across the country, Centers for Disease…