PhD Student Researh Department of Practice and Policy, School of Pharmacy, University College London, London, United Kingdom London, United Kingdom
Background: Long COVID is such an iconic topic which affects the human’s health and well-being globally. Despite the growing volume of long COVID research, the crucial matter of how it is defined has not been universally agreed.
Objectives: To describe the way how long COVID has been defined so far in the long COVID or post-COVID studies.
Methods: We conducted a descriptive study on long COVID definition following the STROBE guideline and performed the literature search using PRISMA checklist in PubMed on 26 October 2022. 7,087 studies containing information on long COVID or post-COVID were identified from 1 February 2020 - 26 October 2022 using the keywords “((long?covid) OR (post?covid)) AND (obsver* OR cohort* OR cross?section* OR case?control OR longitud* OR case?report OR case?series)”. Long COVID definition, study type, country where the study was conducted, and manuscript submission date were extracted from the studies and results were presented chronologically. Two investigators reviewed the studies and screened titles/abstracts independently to determine whether the studies had followed the definition of long COVID from The UK’s National Institute for Health and Care Excellence (NICE), the World Health Organisation (WHO), Centers for Disease Control and Prevention (CDC), other, or none at all. A 10% sample of data collected from the studies were cross-checked by the investigators. When submission dates were not available, the publication dates were used to determine the study time. Ethical approval is exempted as this is a non-invasive, non-interactive study without involving any individual patients.
Results: Among 7087 studies, we excluded 6,972 which were not relevant to long COVID conditions. The remaining of 295 studies were included in the analysis consisting of 2 (0.7%) randomised controlled trials, 134 (45.4%) cohort studies, 66 (22.4%) cross-sectional studies, 13 (4.4%) case-control, 45 (15.3%) case reports or case-series studies and 35 (11.9%) studies used other study designs. 167 (56.6%) studies (were conducted in European countries. We found that 102 (34.6%) studies used the one of the three definitions for their studies (NICE: 56, WHO: 31 and CDC: 15). 193 studies did not follow any of the WHO, NICE, or CDC definitions and 6 studies were submitted before NICE released the long COVID definition. Of 193 studies which did not follow any of these three definitions, 129 (43.7%) used their own definitions for long COVID, whilst 64 (21.7%) did not define long-COVID in their studies.
Conclusions: We found substantial heterogeneity in defining long COVID in the published studies with 65.4% not complying with the definitions from NICE/CDC/WHO. A clearer definition of long COVID is required so that the trial evidence can be reliably applied to clinical practice.
