Half as many American nonsmokers are exposed to secondhand smoke now as a decade ago, but federal researchers remain concerned about high exposure among black nonsmokers, especially children, and people living below the poverty level. 

The Centers for Disease Control and Prevention released a report Tuesday saying that 58 million Americans were exposed to secondhand smoke in 2011-12, or about 1 in 4 nonsmokers. The total is down from about 1 in 2 nonsmokers who were exposed to secondhand smoke in 1999-2000.

However, the decline in secondhand smoke among blacks was less pronounced, falling to about 47% of the black population in 2011-12 from nearly 74% a decade earlier. Exposure among black children between the ages of 3 and 11 remained high at about 68%, nearly twice the level of white (37%) and Mexican-American (30%) children, the report said.

CDC epidemiologist Dr. Brian King credited smoke-free laws in 26 states and about 700 cities with helping slash secondhand smoke exposure over the past decade. “We’ve seen a marked decline in secondhand smoke exposure, however, the prevalence still remains alarmingly high and there’s also marked disparities,” Dr. King said.

The percentage of people living in poverty who were exposed to secondhand smoke fell to about 43% in 2011-12 from nearly 72% in 1999-2000. The exposure level for those living above the poverty level was about 21% in 2011-12; it was 48% in 1999-2000.

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