Resources for state health and environment agencies working together to reduce asthma in children. Sponsored by ECOS.

Back to asthma health data resources

How many people have asthma in the US?

Nearly one in thirteen children in the US have asthma, and this percentage is growing more rapidly in preschool age children than in any other group. (2)

Is asthma increasing?

Asthma is increasing in the US and around the world. The National Heart, Lung, and Blood Institute reports that the prevalence of asthma around the world has doubled in the last 15 years (1). In the US, the Centers for Disease Control estimates that prevalence among persons up to 17 years old increased about 5% per year from 1980 to 1995. (4)

In the US, the rates of deaths from asthma, hospitalizations and visits to emergeny rooms have been increasing for more than 20 years, particularly among children and African Americans. Since 1979-1982, the death rate for blacks has increased 71% while for whites it increased 41% (1).

What kind of data do we have about how many people have asthma and whether this is increasing?

Data about asthma is more limited than data for many other important diseases.

It is difficult or impossible to estimate the annual incidence of asthma in the US. "Incidence" means the number of new cases diagnosed over the period of a year. Looking at the incidence of a disease is the best way to determine how the frequency of the disease changes over time.

Asthma is usually presented as "prevalence." This means the number of people who have the disease in a population at a particular point in time. Prevalence is a less informative way of looking at changes in the rate of disease because it depends on two factors -- how many people get the disease and how long they have the disease. It is harder to see changes in frequency when looking at prevalence numbers than when looking at incidence numbers.

What are the main data sources for asthma?

Data about asthma is usually one of these four sources:

Death certificate or vital statistics -- this source is useful for looking at he number of cases of asthma that were not managed successfully through medical care, but it is not a very good indicator of how the frequency of the disease is changing because most people do not die of asthma, and in many cases deaths represent a failure of care. Almost all states report mortality data, and there is a national data system for this information -- the National Vital Statistics System maintained by the National Center for Health Statistics.

The Healthy People 2010 project reports that the rate of asthma deaths in children are 2.1 per million for children under 5 and 3.3 per million for children from 5 to 14. The goal is to reduce these rates. (3)

Hospital discharges or hospitalization data -- this source provides information about the number of cases of asthma that were serious enough to require admission to a hospital. These cases represent serious cases of asthma. The frequency of hospital discharge or hospitalization is also influenced by access to care. Those without health insurance are less likely to be admitted to the hospital than others. Several states consider hospital discharge or hospitalization data.

The Healthy People 2010 project reports that the rate of asthma hospitalizations in children under 5 are 45.6 per 10,000 and 12.5 per 10,000 for children over 5 and adults. The goal is to reduce these rates. The national data system is the National Hosptial Dischrage Survey conducted by the National Center for Health Statistics. (3)

Emergency room visits for asthma -- this source provides information about the number of cases of asthma that required treatment at an emergency room. This represents serious cases of asthma in general. However, some uninsured people are likely to be treated in an emergency room who might have been admitted to a hospital if they had health insurance. Also, people who do not receive regular medical care and assistance to manage their asthma on a day to day basis are more likely than others with similar severity of asthma to end up in an emergency room. So, people without good access to medical care are likely to be over-represented in emergency room visit statistics.

For environmental studies, investigators generally view emergency room visits as the most sensitive indicator of adverse environmental conditions that contribute to disease on a daily basis. A few states consider emergency room visits data.

The Healthy People 2010 project reports that the rate of ER visits for children under 5 was 150 per 10,000 and 71.1 per 10,000 for children over 5 and adults. The goal is to reduce these rates. The national data source is the National Hospital Ambulatory Medical Care Survey conducted by the National Center for Health Statistics. (3)

Health Survey Data - Surveys of people to ask them about their health are conducted by agencies such as the National Center for Health Statistics.

The National Health Interview Survey asks questions about asthma. It is used as a source of national estimates of the prevalence of asthma. This survey does not break down data by state and does not interview enough people to allow for state level estimates.

The Behavioral Risk Factors Surveillance Survey (BRFSS) focuses largely on asking people about their own actions that may affect their health. It asks questions about how much people smoke and how much they exercise, for example. The survey is conducted at the state level and produces information for individual states. A module of questions about asthma have been developed for this survey, and some states have reported that they will be including these questions in future surveys.

School surveys - School districts in some states collect some information about asthma. There does not appear to be a standard format for this data. It appears that schools in some states may report asthma cases that are treated by school nurses and other states may survey students or parents about asthma and report something more like prevalence estimates.

Health care utilization data - Data provided through the health care system can be used to estimate asthma incidence or prevalence, as well as severity. This requires that all medical treatment information for a defined population be available in a standard format. This is the case for populations who have government health services, such as those who receive Medicaid. The records of health care for Medicaid-eligible persons can be used to estimate asthma. Several states look at this type of data. Information from health insurance services made available to children outside Medicaid might also be possible to use for this purpose.

What are the priorities for tracking of asthma?

Several studies that have considered how to improve the current system suggest that a national system would be a priority. At present, different states look at different kinds of data. It does not appear that state efforts are converging toward any particular approach to improving data collection and tracking.

Health Track, a project of the Pew Trusts, recommended a national tracking system for asthma, as have several other strategy documents.

References Cited

1. National Institutes of Health. National Heart, Lung, and Blood Insitute. 2001. Data release for World Asthma Day, May 2001.

2. President's Task Force on Environmental Health Risks and Safety Risks to Children. Asthma and the Environment: A Strategy to Protect Children. Revised May 2000.

3. US Department of Health and Human Services. Tracking Healthy People 2010. Section 24 - Respiratory Diseases. November 2000. http://www.cdc.gov/nchs/hphome.htm.

4. CDC. Measuring childhood asthma prevalence before and after the 1997 redesign of the National Health Interview Survey -- United States. Mortality and Morbidity Weekly Report. 49(40): 908-911. October 13, 2000. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm4940a2.htm