About nine percent of all asthma cases in the United States are caused or made worse by work-related exposures, a new federal study says.

That means work-related asthma affects about 1.4 million adults annually, the researchers said.

State-by-state rates of workplace-related asthma ranged from 4.8 percent (Arizona) to just over 14 percent (Florida), according to the study by researchers at the U.S. Centers for Disease Control and Prevention.

The analysis of 2006-09 data from 38 states and the District of Columbia also suggests that older workers and those in certain ethnic or minority groups are most at risk. For example, rates of employment-related asthma were 12.7 percent for people ages 45-64 vs. about 7 percent for people ages 18-44. Among racial groups rates of work-related asthma were 12.5 percent for blacks, 10.5 percent for Hispanics and 8.2 percent for whites, the report found.

The estimated proportion of adults with current asthma who had work-related asthma was similar for men and women, at about nine percent.

Asthma linked to on-the-job exposures is a preventable but under-recognized illness and the new findings highlight the need to expand workplace surveillance to better understand the risk factors and to better focus prevention efforts, the researchers said.

Better surveillance of the problem "would enhance our understanding of work-related asthma epidemiology and enable states, other government agencies, health professionals, employers, workers and worker representatives to better target intervention efforts to reduce the burden of work-related asthma," the researchers wrote in a summary.

The study appears in the May 25 issue of the CDC's Morbidity and Mortality Weekly Report.