NEW YORK, June 19 (Reuters) - Self-reported U.S. asthma rates have fallen significantly for the first time in four years to a nine-year low, according to a survey released on Thursday, but researchers cautioned that the numbers may not mean the disease is dwindling.
About 7.4 percent of the U.S. population reported having asthma in 2013, down from a level that has hovered around 8.5 percent since 2009, the U.S. Centers for Disease Control and Prevention survey found.
That drop represents about 3 million U.S. children and adults, CDC statistician Jeannine Schiller told Reuters.
Fewer episodes of the disease, which can causes wheezing, breathlessness and coughing, were also reported.
Last year, 3.8 percent of the population said they experienced an asthma attack, a rate not seen in over a decade and a half. In 2012, 4.4 percent of those polled reported an attack.
But Schiller said she was not quite ready to declare asthma's decline.
"We've all been kind of scratching our heads" at the finding, she said. "We have no reason not to believe it, but I think it is important to just be cautious about it."
The findings could be a statistical anomaly rather than a sign that the country has made major strides in combating the disease, Schiller said.
CDC's National Health Interview Survey polled about 47,000 people in the United States during 2013 on their experiences with asthma.
Black children saw some of the steepest declines in the disease, falling to a rate of 13.1 percent from 16.4 percent in the previous year, the study found.
Asthma is among the most prevalent long-term diseases among children, according to the CDC, although adults are also affected. While its causes are not yet fully known, environmental factors like tobacco smoke, cockroaches and mold can trigger attacks. (Reporting by Curtis Skinner; Editing by Scott Malone and Susan Heavey)