HEALTH & SCIENCE

Childhood asthma rates are leveling off, but disparities remain

A two-decade trend of increases in prevalence among children may be ending, but more data to confirm the encouraging changes are needed.

By Stephanie Stapleton, AMNews staff. Aug. 26, 2002. Additional information

Washington -- Is childhood asthma prevalence plateauing?

Experts wonder whether a recent analysis of the illness' trends may signal changes in the disease's burden. But significant questions persist, making it too soon to know for sure.

According to a study appearing in the August issue of Pediatrics, asthma prevalence increased an average of 4.3% per year between 1980 and 1996. The number appeared to peak with a 7.5% increase in 1995. From 1997 to 2000, asthma attack prevalence statistics leveled off.

But this doesn't alter the real problem of childhood asthma.

"There is still more asthma than we can possibly take care of," said Robert Wood, MD, associate professor of pediatrics at Johns Hopkins University, Baltimore.

But the analysis, which was led by Lara J. Akinbami, MD, of the Centers for Disease Control and Prevention's National Center for Health Statistics, is being viewed as encouraging.

"Data suggest that the burden for childhood asthma may have recently plateaued ... although additional years of data collection are necessary to confirm a change in trend," wrote Dr. Akinbami and colleagues. However, "racial and ethnic disparities remain large for asthma health care utilization and mortality."

The study, based on five national data sources, produced a comprehensive description of trends in childhood asthma prevalence, health care utilization, and mortality in the United States.

Among the numbers: Asthma office visits increased by an average of 3.8% each year from 1980 to 1999. Hospitalization increased 1.4% each year during this period. Deaths increased 3.4% per year from 1980 to 1998.

Overall, children 4 and younger had the largest increase in prevalence and greater health care use, but adolescents had the highest mortality. Also, the asthma burden was borne disproportionately by black children.

In 1997, the first year a newly designed childhood asthma measure was used in the National Health Interview Survey design, asthma attack prevalence was 5.4%.

It is also important to note that there has been considerable year-to-year variability in the upward trend of the 1980s and 1990s. "You have to look at the entire picture over several years," explained Dr. Akinbami.

"This is good news," she said. However, the post-1997 measure -- which tracks children who have had at least one asthma attack in the past year -- cannot be directly compared to previous asthma prevalence. "We can't be completely sure that if the survey wasn't redesigned, the recent trend would still look the same," she said.

Still, the numbers are important. "[They] give a very general picture of how well the message is getting to people with asthma about how best to control their symptoms and keep the disease in check," she said.

But there are nagging questions that persist about the factors behind the increase. They make filling in the details perplexing.

Among the possible explanations for increased prevalence in the 1980s through mid-1990s is the notion of diagnostic transfer. This phenomenon involves a change in the labeling of respiratory conditions in children from other illnesses to asthma, thereby contributing to the jump in prevalence and health care utilization.

"Although not definitively, the study suggests [this] could have played a role ... over the past two decades," explained Dr. Akinbami. Respiratory conditions may have been more likely over time to be diagnosed as asthma than as other things because of increasing awareness and education about the disease, she said. It is possible that diagnostic transfer has slowed recently because now most patients are accurately diagnosed. "But that is just my opinion -- our study wasn't designed to answer this question," she said.

Voices from the trenches do acknowledge this phenomenon occurs.

Some increase in prevalence could have resulted from these diagnosis patterns -- but not a majority, said Linda B. Ford, MD, allergist at the Asthma and Allergy Center in Lincoln, Neb., and spokeswoman for the American Academy of Allergy, Asthma, and Immunology. Still, it makes the data plateau even more encouraging.

Physicians have in the past sometimes avoided using the diagnosis of asthma in order to not label a child with this illness. It's an approach that could be problematic for health insurance reasons, Dr. Ford said. "I've always thought this was a disservice to the child." Insurance companies can read between the lines to see that certain bronchial illnesses are euphemisms for asthma, she said. Meanwhile, the child does not have the advantage of treatment and education resources related to asthma.

Other oft-cited forces at work include changing environmental exposures and urbanization. However, the article notes that evidence is mixed.

But Dr. Ford notes that environmental influences are one of the areas in which many questions remain. Tobacco use is decreasing, she said, and some environmental rules are helping reduce pollution. "I wonder if we can get our air cleaner, will it follow that in time we will see the trend in asthma decrease?" she asked.

Meanwhile, the journal article offers the notion that public health interventions may be behind the recent plateau in hospitalizations and deaths. The State Children's Health Insurance Program, which was responsible for increasing children's access to health care, may be partly responsible for the large jump in asthma office visits in 1998.

Similarly, the National Asthma Education and Prevention Program Guidelines, issued in 1997, are sometimes credited with the decline in asthma mortality in the United States. Other public health research regarding primary and secondary prevention efforts also likely played a role.

Only partially understood

But just as the causes of asthma are only partially understood, the factors behind the increase and the recent apparent plateau are likely to be complex, too. "This means that strategies to address and prevent asthma will have many components, and the very large asthma burden that we still face will need to be addressed on many fronts," said Dr. Akinbami.

And it will be no easy task.

"At this point, I don't think we understand the reasons behind the numbers well enough," said Dr. Wood. "We need to know why the rates have done what they've done. We need to gather more data."

Patterns among different racial and ethnic groups, for example, are still important. Though much has been made of disparities in asthma prevalence, much larger gaps exist in regard to morbidity and mortality.

But overall, the picture provided by this study is useful and important.

"Anytime you can take a picture of something -- a snapshot -- it is helpful," said Dr. Ford. "It gives more insight, more information. And gives encouragement that maybe what we are doing is right. Maybe we can make a difference."

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A recent data analysis highlighted a plateau in childhood asthma attack prevalence rates since 1997. For almost two decades, childhood asthma prevalence had demonstrated a marked and unexplained increase, climbing from 36.8 cases per 1,000 in 1980-81 to 68.6 cases per 1,000 in 1995-96.

Race/ethnicity

           White   Black  Hispanic   All 
           -----   -----  --------  ----
1980-81*    36.4    41.9     na     36.8
1985-86     51.0    59.8    31.5    49.4
1990-91     59.6    72.6    51.2    60.1
1995-96     65.3    82.1    76.1    68.6
1997        52.2    67.5    51.3    54.4
1998        52.1    68.1    47.4    53.1
1999        49.9    74.1    44.5    52.7
2000        53.4    76.8    42.1    55.3

Age

             0-4    5-10    11-17    All
            ----    ----    -----   ----
1980-81     29.4    49.0    32.1    36.8
1985-86     31.9    54.5    58.0    49.4
1990-91     43.0    62.7    71.4    60.1
1995-96     50.3    74.3    77.4    68.6
1997        41.2    58.5    60.4    54.4
1998        46.5    53.0    58.0    53.1
1999        42.1    57.2    56.2    52.7
2000        43.5    57.5    61.5    55.3

Source: Adapted from "Trends in Childhood Asthma: Prevalence, health care utilization and mortality;" Pediatrics, August. Notes: For 1980-81, Hispanic data are not disaggregated; "Black " and "white" refer to non-Hispanics in subsequent years. There is a trend break between 1995-1996 and 1997 due to the redesign of the 1997 National Health Interview Survey. Data from 1980 to 1996 reflect average annual asthma prevalence. Data since 1997 reflect asthma attack prevalence per 1,000 during the previous 12 months among children younger than 18.

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Abstract, "Trends in Childhood Asthma: Prevalence, Health Care Utilization and Mortality," Pediatrics, August (vol. 110, issue 2) (http://www.pediatrics.org/cgi/content/abstract/110/2/315)

American Academy of Allergy, Asthma and Immunology (http://www.aaaai.org/)

American College of Allergy, Asthma and Immunology (http://allergy.mcg.edu/)

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Copyright 2002 American Medical Association. All rights reserved.