Asthma Prevalence

Asthma is a chronic respiratory disease characterized by inflammation of the airways and lungs. During an asthma attack, the small airways leading to the air sacs in the lungs are constricted and inflamed, and as a result, less air is able to flow out of the lungs. Asthma attacks can cause a multitude of symptoms ranging in severity from mild to life-threatening. These symptoms include wheezing, breathlessness, chest tightness, and coughing. Currently, there is no cure for asthma; however, people who have asthma can still lead productive lives if they control their asthma (NHLBI, 2014). Taking medication and avoiding contact with environmental "triggers" can help control asthma.

A family history of asthma contributes to susceptibility, but mostly what causes the development of asthma is unknown. Environmental exposures such as environmental tobacco smoke, dust mites, cockroach allergen, outdoor air pollution (e.g., ozone, particulate matter), pets, and mold are considered important triggers of an asthma attack (CDC, 2016; U.S. EPA, 2005, 2007).

Statistics for period asthma prevalence, current asthma prevalence, and asthma attack prevalence are based on national estimates from the National Health Interview Survey (NHIS), conducted by the Centers for Disease Control and Prevention's (CDC's) National Center for Health Statistics (NCHS). The NHIS is the principal source of information on the health of the civilian non-institutionalized population of the U.S. and since 1960 has been one of the major data collection programs of NCHS. Period asthma prevalence (pre-1997 data) represents survey participants who had asthma in the past 12 months. To determine current asthma prevalence, adults/children who had ever received an asthma diagnosis from a healthcare practitioner were asked whether they still have asthma. Asthma attack prevalence is based on the number of adults/children with an asthma diagnosis who reported an asthma episode or attack in the past 12 months.

From 2012 to 2014, approximately 7.8 percent of the U.S. population reported that they currently have asthma (NCHS, 2016a; data not shown). Reported asthma prevalence is highest in the child and adolescent population.

Adult Asthma

In 2014, over 17 million adults within the U.S. (age 18+ years) were reported as still having asthma and over 8 million reported experiencing an asthma episode or attack during the previous 12 months (NCHS, 2016b; data not shown).

As shown in Exhibit 1, between 2002 and 2014 current asthma prevalence has ranged from approximately 64 cases per 1,000 (2003) to 82 cases per 1,000 (2010). During this same time period, asthma attack prevalence has varied slightly, from a low of 33 cases per 1,000 occurring in 2003 to a high of 42 cases per 1,000 occurring in 2010.

Exhibit 2 compares age-adjusted asthma prevalence across racial and ethnic groups for the 2012-2014 time period. Blacks reported the highest current asthma prevalence across racial groups (92 cases per 1,000), followed by American Indians/Alaska Natives (87 cases per 1,000), whites (73 cases per 1,000), and Asians (44 cases per 1,000). American Indians/Alaska Natives reported the highest asthma attack prevalence (49 cases per 1,000), followed by blacks (43 cases per 1,000), whites (36 cases per 1,000), and Asians (19 cases per 1,000).

Exhibit 2 also compares both asthma prevalence categories for total Hispanics, non-Hispanic whites, and non-Hispanic blacks. For current asthma prevalence in adults, 59 cases per 1,000 were reported in total Hispanics, 78 cases per 1,000 in non-Hispanic whites, and 92 cases per 1,000 in non-Hispanic blacks. For asthma attack prevalence in adults, 29 cases per 1,000 were reported in total Hispanics, 38 cases per 1,000 in non-Hispanic whites, and 43 cases per 1,000 in non-Hispanic blacks.

Childhood Asthma

In 2014, over 6 million children within the U.S. (age 0-17 years) were reported as having current asthma and over 3 million reported experiencing an asthma episode or attack during the previous 12 months (NCHS, 2016b; data not shown).

As shown in Exhibit 3, crude period asthma prevalence increased on average approximately 4 percent per year between 1980 and 1996 (Akinbami et al., 2009). Rates in subsequent years (1997-2014), reported for current asthma and asthma attack prevalence, show no sharp upward or downward change through most of the time period. Since tracking began in 2001, current asthma prevalence has ranged from approximately 83 cases per 1,000 (2002 and 2013) to 96 cases per 1,000 (2009). Between 1997 and 2014, asthma attack prevalence has varied slightly, with the lowest rate of 43 per 1,000 occurring in 2014, the most recent reporting year, and the highest rate of 58 cases per 1,000 occurring in 2002.

The overall pattern of asthma prevalence across races in children during 2012-2014 is similar to that seen in adults (Exhibit 4). During the 2012-2014 period, reported current asthma prevalence was highest among black children (142 cases per 1,000), followed by American Indians/Alaska Natives (102 cases per 1,000), whites (77 cases per 1,000), and Asians (51 cases per 1,000). Asthma attack prevalence rates across racial groups followed a similar pattern to the reporting of current asthma prevalence. This exhibit also shows a similar pattern observed among children as seen with adults, with a higher number of cases of asthma attack observed among non-Hispanic blacks than non-Hispanic whites and total Hispanics.

• The NHIS questionnaire underwent major changes in 1997, and with the exception of Exhibit 3 that shows historical data for children, the data presented focus on surveys conducted from 1997 (children) and 2002 (adults) to the most currently available release (2014). The redesigned NHIS is different in content, format, and mode of data collection from earlier versions of the survey. Due to changes in methodology, 1997-2014 NHIS estimates are not directly comparable to pre-1997 NHIS estimates.

• Prevalence data reported in the NHIS are based on self-reported responses to specific questions pertaining to airway-related illnesses, and are subject to the biases associated with self-reported data. Self-reported data may underestimate the disease prevalence being measured if, for whatever reason, the respondent is not fully aware of his/her condition.

Current asthma prevalence data in Exhibits 1 and 3 were obtained from annual reports and standalone tables published by NCHS (NCHS, 2004a,b, 2005a,b, 2006a-d, 2007a,b, 2008a,b, 2009a,b, 2010a,b, 2011, 2012a-c, 2014a,b, 2015a-d), which summarize health statistics compiled from the NHIS (http://www.cdc.gov/nchs/nhis/nhis_series.htm and http://www.cdc.gov/nchs/nhis/shs.htm). Asthma attack prevalence data from 2002 to 2014 for Exhibits 1 and 3 were obtained by running Stata analyses on the NHIS public-use data files (NCHS, 2016b), and obtained from annual reports for 1997 to 2001 data in Exhibit 3 (2002a,b, 2003a-c). Race and ethnicity data for Exhibits 2 and 4 were obtained from CDC's NCHS (NCHS, 2016a). The data used to create these exhibits for 2012-2014 originated from the NHIS. The pre-1997 data also originate from the NHIS, as compiled by NCHS in Akinbami et al. (2009).