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Definitions of asthma varied widely in prevalence studies

The operational definitions of asthma were diverse in published epidemiological prevalence studies, according to recent study results.

Researchers in Portugal and France conducted a systemic literature search of the Thomson Reuters ISI Web of Knowledge for cross-sectional studies containing an explicit definition of asthma. The terms “asthma” and “prevalence” were in the title.

The initial search included the 100 most-cited papers in studies published between January 2010 and October 2013. Papers in English, Portuguese, Spanish and French were included, with the asthma definition used and other variables recorded. The definitions were then applied to the data of the Portuguese National Asthma survey (INAsma) and the 2005-2006 National Health and Nutrition Examination Survey (NHANES), with asthma prevalence estimates computed for different definitions.

There were 1,738 papers gathered using the search terms, and 117 were selected for the study. Thirty-four papers defined lifetime asthma; 54 papers, diagnosed asthma; and 61 papers, current asthma. The terms were defined in eight, 12 and 29 distinct ways, respectively.

When the definitions of current asthma were applied to the INAsma data, prevalence ranged from 5.3% to 39.5%, while for NHANES data, prevalence ranged from 1.1% to 17.2%.

“There is considerable heterogeneity in the definitions of asthma used in epidemiological studies leading to highly variable estimates of asthma prevalence,” the researchers wrote. “Studies to inform a standardized operational definition are needed.

“Based on the data presented, we propose an initial comprehensive set of questions that can be used in validation studies while allowing comparisons with previous prevalence studies of asthma.”

Disclosure: The researchers report no relevant financial disclosures.