Akinbami and Schoendorf Respond to “Asthma Surveillance in US Children” The Challenge of Asthma Surveillance and Continuous Health Surveys

Drs. Lanphear and Gergen (1) correctly point out that there are many challenges in conducting asthma surveillance and that continuous improvement in national asthma surveillance is needed. They also point out that the data collection systems of the National Center for Health Statistics are the cornerstone of many national surveillance systems. They go on to identify several shortcomings of the National Health Interview Survey (NHIS), one component of the asthma surveillance system. Most of these shortcomings are directly related to the complexities of asthma surveillance in particular but also reflect challenges in operating any ongoing data collection system. Maintaining continuous data collection is a major objective of the NHIS. However, to keep the NHIS useful for its many purposes, it was essential that the survey be redesigned to reduce respondent burden and thus preserve high response rates, to utilize new interviewing technology, to simplify the NHIS data set for increased ease of use by researchers, and to incorporate new medical knowledge. There is no good time to redesign a survey; issues of a break in trend are always of concern. However, what is lost in data comparability can be gained in improved quality and, indeed, the redesign in many ways improved asthma surveillance. For example, prior to the redesign, the NHIS did not require a physician diagnosis for the case definition of asthma. Starting with the 1997 redesign, asking about physician diagnosis was one important change made for all chronic conditions to improve data quality. The 1997–2000 NHIS did indeed have some shortcomings for asthma surveillance beyond the interruption of the trend. As discussed in our article (2), from 1997 through 2000, the core survey did not include a question about current asthma, but focused on asthma attacks or episodes. In 2001, a question about current asthma was added to fill this gap. Data from the 2001 NHIS for asthma prevalence are available on the National Center for Health Statistics Internet page (http://www.cdc.gov/nchs/products/pubs/pubd/ hestats/asthma/asthma.htm). Starting in 2001, the four asthma questions in the NHIS core (lifetime diagnosis, current asthma, recent asthma attacks, and emergency room visits for asthma) are identical to the asthma questions in the National Health and Nutrition Examination Survey, as recommended by Drs. Lanphear and Gergen. Also as suggested by Drs. Lanphear and Gergen, additional questions about asthma medications, patient education, and hospitalization are included in periodic topical modules. The 1999 NHIS included a topical asthma module that also contained questions about symptoms of wheezing, allowing the rate of asthma diagnosis among symptomatic people to be measured. The national asthma surveillance system of the Centers for Disease Control and Prevention comprises several surveys and data systems: the NHIS, the Behavioral Risk Factor Surveillance System, the National Ambulatory Medical Care Survey, the National Hospital Ambulatory Medical Care Survey, the National Hospital Discharge Survey, and the Mortality Component of the National Vital Statistics System. Although each data source has its strengths and weaknesses, taken together, the asthma surveillance system of the Centers for Disease Control and Prevention provides a broad view of the impact of asthma in the United States. Furthermore, this system, along with the National Health and Nutrition Examination Survey, provides rich information that has been widely utilized in research on asthma. The National Center for Health Statistics and other Centers in the Centers for Disease Control and Prevention have been working to improve and augment existing asthma surveillance. One area of particularly high interest is