A new survey suggests asthma in the U.S. may finally be on the decline. But the results are so surprising that health officials are cautious about claiming a downturn.
"I wouldn't say it's good news — yet," said the study's lead author, Jeannine Schiller of the U.S. Centers for Disease Control and Prevention.
The findings come from a large national health survey conducted last year. The drop could just be an unexplained statistical blip, and Schiller said she's waiting for data from this year before proclaiming asthma is on the decline.
The CDC released the report Thursday.
For the past few years, about 8.6 per cent of Americans have said they have asthma. But in last year's survey, 7.4 per cent said they currently had it. That was the lowest mark in a decade, and represents a decline of more than 3 million people.
The largest declines were seen in black children and women.
There was also a drop in those who said they'd had an asthma attack or episode in the past year. The number fell from 4.4 per cent in 2012 to 3.8 per cent last year — the lowest mark in more than 15 years.
The new survey involved in-person interviews of more than 47,000 Americans and covered both adults and children.
Asthma can cause bouts of coughing, wheezing, and chest pain. Experts aren't sure what causes it, but asthma attacks can be triggered by things like tobacco smoke, air pollution, pollen, and cockroaches. Studies have pointed at decrepit housing and climate change as some of the possible reasons for the increase in asthma seen in the past decade.
The disease can be controlled through medication. Some studies have shown a gradual decline in the percentage of asthma patients who said they suffered an attack in the previous year.
Experts say there's been no recent major advance in asthma treatment or improvement in the environment that would account for the latest figures.
"Nationally, I'm not aware of anything that would explain these statistics," said Dr. Karen Freedle, an Emory University specialist in pediatric asthma.
In 2010, 8.5 per cent of Canadians aged 12 and older reported that they had been diagnosed with asthma. The rate did not change significantly from 2001 to 2010, according to Statistics Canada's website.