The eight-county Sierra county region including Amador, Tuolumne and Calaveras counties reported a below-average number — 6 percent — of people who have been diagnosed with asthma. But the region ranked highest in the state in the percentage of people who have not been diagnosed with asthma but suffer from asthma-like symptoms or breathing problems — 16 percent. The Sierra Counties joint sub group is used in the study due to the relatively small populations of the counties and the fact that individual county statistics are not available. Many factors are cited in the increase of asthma, one being Americans usage of anti bacterial products- children raised in dustier environments are less likely to exhibit asthma symptoms later in life. Also rural counties have a high number of homes that use wood-burning stoves as their primary source of heat, compared to urban counties.

Smoke produced from those stoves pollutes the air with particulate matter that can deposit itself in lungs and trigger asthmatic symptoms. More-urban counties, with more automobile traffic, typically have higher levels of non-particulate air pollution, such as ozone and car exhaust fumes, which are also asthmatic irritants. Among findings that should have far-reaching implications for California's healthcare system, nearly 6 million Californians report that they have difficulty breathing. "Clearly, asthma and other breathing problems are significant issues for Californians, and a growing challenge for our healthcare system," said Susan H. Babey, PhD, lead author of the study and a research scientist at the UCLA Center for Health Policy Research. The study also shows that asthma and asthma-like breathing problems disproportionately affect young children, African Americans and American Indian/Alaska Natives. About 19 percent of children age 5 and younger experience asthma or asthma-like symptoms, the most of any age group and 4 percentage points higher than ages 18 to 24, which has the lowest. About 34 percent of American Indian/Alaska Native adults suffered from asthma symptoms or other breathing problems, compared to 20 percent of African American adults, 19 percent of white adults, 13 percent of Latino adults and 10 percent of Asian adults.