BETHESDA, MD—After several years of increasing, childhood asthma prevalence may have reached a plateau, according to a study from the National Center for Health Statistics (NCHS).[1] However, racial differences in asthma prevalence persist and may even be widening.

Lara J. Akinbami, MD, and Kenneth C. Schoendorf, MD, MPH, analyzed data from 1980 forward to report on trends in asthma—its prevalence and mortality in different racial/ethnic and age groups, as well as disease-related health care utilization—in children ages 0 to 17. Their secondary objective was to measure the effect of the 1997 National Health Information Survey (NHIS) redesign on prevalence estimates.

“The recent plateau in asthma prevalence has been [seen] over the four years after the NHIS was redesigned in 1997 and the measurement of asthma prevalence was changed,” said Dr. Akinbami, a medical epidemiologist at the Infant and Child Health Studies Branch of the NCHS in Bethesda, Maryland. This suggests that the plateau is real and not just a result of the survey’s redesign.

The redesigned measurement estimates the number of children who have had an asthma attack in the past 12 months. In an interview with RESPIRATORY REVIEWS, Dr. Akinbami explained, “It is an estimate of how many children do not have control over their asthma and are at risk of poor asthma outcomes, such as missing school, being hospitalized, and in rare cases, dying from asthma.”

The investigators analyzed information from five NCHS data systems: the NHIS, the National Ambulatory Medical Care Survey, the National Hospital Discharge Survey, the National Hospital Ambulatory Medical Care Survey, and the mortality component of the National Vital Statistics System.

ASTHMA RATE STABILIZED IN THE 90S

Overall asthma prevalence among children increased from 36 out of 1,000 in 1980 to 75 out of 1,000 in 1995. It then decreased in 1996 to 62 out of 1,000 children. According to the 1997 redesigned NHIS, the overall asthma attack prevalence was 54 out of 1,000 children. That prevalence remained stable between 1997 and 2000.

From 1980 to 1996, asthma prevalence increased most rapidly in children ages 0 to 4; smaller increases in prevalence were seen in other age-groups. From 1997 to 2000, asthma attack prevalence remained fairly level among all age-groups. The childhood asthma hospitalization rate began to increase slowly in 1980, but appeared to have reached a plateau by the mid-1990s.

Whether the rise in asthma deaths has also plateaued is unclear. The overall death rate rose by 3.4% per year between 1980 and 1998. It peaked at 3.8:1 million children in 1996, then declined in 1997 to 3.1:1 million children. In 1998, asthma mortality rose again, to 3.5:1 million.

RACIAL DIFFERENCES PERSIST

Asthma continues to affect black children disproportionately (Figure 1). In fact, asthma attack prevalence rates in black children continued to rise between 1997 and 2000, although the rate of increase was markedly lower than that seen in the 1980s or early 1990s.

Figure 1 Asthma Prevalence, 1980-2000*

* Gap between 1995-1996 and 1997 indicates a break in trend due to the redesign of the 1997 NHIS. Source: Data extracted from Akinbami LJ et al. Pediatrics. 2002.

Hospitalization rates for asthma also remain markedly higher for black children. In 1998-1999, the hospitalization rate was 3.6 times higher in black children than in white children.

Black children also had the highest asthma death rates throughout the 20-year study—and the greatest increase over time. In 1985-1986, the death rate among black children was 4.1 times higher than that for white children. In 1997-1998, the asthma death rate was 4.6 times higher among black children.

MORE CHILDREN ARE DIAGNOSED

Dr. Akinbami and colleagues acknowledge that diagnostic transfer—the labeling of other respiratory conditions as asthma—may have contributed to the increase in asthma prevalence and health care utilization during the 1980s and 1990s. Although they designed their study to test for this hypothesis, results were inconclusive. “It is possible that diagnostic transfer has slowed recently because now more patients are accurately diagnosed as having asthma,” suggested Dr. Akinbami.

The redesign of the NHIS in 1997 has complicated interpretation of trends in asthma prevalence. The 1996 NHIS sample size was reduced by 40% as a result of pilot testing of the redesign. The impact of this decreased sample size on the 1996 prevalence estimates is still unclear. However, said Dr. Akinbami, data from the National Hospital Discharge Survey and the Vital Statistics System also indicated a plateau in childhood asthma hospitalizations and deaths after 1996.

Dr. Akinbami believes that the present findings are promising, but not wholly so. “The good news is that for the time being, we appear to have reached a plateau on the asthma mountain. The bad news is that we are already high up on that mountain.” She noted that additional years of data collection are needed to confirm a change in trend.

“While a pause or reversal in the increases in childhood asthma is very welcome, there remains much work to do on many fronts to address the large costs of childhood asthma and improve outcomes for affected children,” Dr. Akinbami concluded.

—Gale Jurasek