US Asthma Prevalence Plateauing, but Not Among the Poor

Ricki Lewis, PhD

December 28, 2015

Rates of asthma prevalence in the United States are leveling off and possibly declining, but not among the poor, according to a study published online December 28 in Pediatrics.

Overall prevalence of childhood asthma doubled from 1980 (3.6%) to 1995 (7.5%), increased at a slower rate from 2001 (8.7%) to 2009 (9.7%), and dipped in 2010 (9.3%). The 1980s saw no or little disparity in asthma prevalence between black and white children, but asthma prevalence doubled for black children by 2010.

Because deeper understanding of the epidemiology of asthma could aid prevention, Lara J. Akinbami, MD, from the National Center for Health Statistics, Centers for Disease Control and Prevention, Hyattsville, Maryland, and colleagues extended analysis of asthma prevalence from 2001 to 2013. They analyzed subgroup differences in answers to the questions "Has a doctor or other health professional ever told you that your child had asthma?" and "Does your child still have asthma?" from the National Health Interview Survey (NHIS).

The results confirm that asthma prevalence among children (aged 0 - 17 years) increased from 2001 to 2008. After 2008, prevalence plateaued and then declined. In 2012, it was 9.3%; in 2013, 8.3%.

After adjustment for factors including gender, age group, poverty status, race/ethnicity, family structure, urbanicity, and geographic region, four characteristics were significant: age group, poverty status (ratio of family income to the federal poverty level: "poor," "near poor," and "nonpoor"), race/ethnicity, and geographic region. Prevalence was similar among 5- to 9-year-olds and 10- to 17-year-olds, but lower among 0- to 4-year-olds. Asthma prevalence increased linearly significantly among poor children, whereas prevalence change was nonlinear for near poor and nonpoor children.

There was no significant trend for non-Hispanic white or Puerto Rican children, but a significant nonlinear trend for non-Hispanic black and Mexican-American children.

The disparity in asthma prevalence between non-Hispanic black and white children peaked in 2011 (prevalence ratio, 2.1; 95% confidence interval [CI], 1.7 - 2.4). It was 1.8 (95% CI, 1.5 - 2.1) in 2013 and lowest in 2001, with a rate ratio of 1.3 (95% CI, 1.1 - 1.6).

Children living in the Northeast and West had no significant trend in asthma prevalence. Children living in the South had an increasing linear trend, and those in the Midwest a nonlinear trend.

The finding that the halt in increasing prevalence among non-Hispanic black children dampened the increasing black–white disparity might reflect a changing definition of "asthma prevalence." Before 1997, researchers used "asthma period prevalence," meaning asthma in the past 12 months. It was similar among black and white children. Starting in 2001, the measure was "current asthma prevalence," reflecting asthma at the time of the health survey. It increased from 40% higher relative disparity in 2001 to 100% in 2010, with the increase attributed to increasing prevalence in black children.

"This analysis of NHIS data cannot answer the question of why trends change but does provide a comprehensive national picture and some insight into the complexity of asthma prevalence," the researchers conclude. They hypothesize that the link to poverty could be increased exposure to environmental triggers.

A limitation to the study is that the NHIS information does not include clinical data or environmental exposures.

The authors have disclosed no relevant financial relationships.

Pediatrics. Published online December 28, 2015.

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