Overview

• Researchers applied five published long COVID definitions from the U.S., U.K., Netherlands, Sweden and Puerto Rico to data from about 4,700 patients in the CDC-funded INSPIRE cohort.
• Prevalence estimates varied from 15% to 42% across the same cohort, suggesting that definitional differences may account for up to one-third of variation between published studies.
• The five definitions differed in required symptom duration—from four weeks to six months—and in the number of symptoms considered, ranging from nine to 44.
• All existing definitions showed only moderate sensitivity and imperfect specificity compared with participant self-reports, underscoring the absence of an objective diagnostic test.
• Study authors urge adoption of a streamlined, parsimonious research definition or clearer transparency about definition choice to improve study comparability and patient care.