Prevalence of Long-term Symptoms Varies When Using Different Post-COVID-19 Definitions in Positively and Negatively Tested Adults: The PRIME Post-COVID Study.

Background: Long-term symptoms after a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection (ie, post-coronavirus disease 2019 [COVID-19] condition or long COVID) constitute a substantial public health problem. Yet, the prevalence remains currently unclear as different case definitions are used, and negatively tested controls are lacking. We aimed to estimate post-COVID-19 condition prevalence using 6 definitions. Methods: The Prevalence, Risk factors, and Impact Evaluation (PRIME) post-COVID-19 condition study is a population-based sample of COVID-19-tested adults. In 2021, 61 655 adults were invited to complete an online questionnaire, including 44 symptoms plus a severity score (0-10) per symptom. Prevalence was calculated in both positively and negatively tested adults, stratified by time since their COVID-19 test (3-5, 6-11, or ≥12 months ago). Results: In positive individuals (n = 7405, 75.6%), the prevalence of long-term symptoms was between 26.9% and 64.1% using the 6 definitions, while in negative individuals (n = 2392, 24.4%), the prevalence varied between 11.4% and 32.5%. The prevalence of long-term symptoms potentially attributable to COVID-19 ranged from 17.9% to 26.3%. Conclusions: There is a (substantial) variation in prevalence estimates when using different post-COVID-19 condition definitions, as is current practice; there is limited overlap between definitions, indicating that the essential post-COVID-19 condition criteria are still unclear. Including negatives is important to determine long-term symptoms attributable to COVID-19. Trial registration: ClinicalTrials.gov Identifier: NCT05128695.