ABSTRACT
Background:
Long COVID is a debilitating multisystem condition. The objective of this study was to estimate the
prevalence of
long COVID in the
adult population of
Scotland, and to identify
risk factors associated with its development.
Methods:
In this national, retrospective, observational
cohort study, we analysed
electronic health records (EHRs) for all
adults (≥18 years) registered with a general medical practice and resident in
Scotland between March 1, 2020, and October 26, 2022 (98-99% of the
population). We
linked data from
primary care,
secondary care,
laboratory testing and prescribing. Four
outcome measures were used to identify
long COVID clinical
codes, free text in
primary care records, free text on sick notes, and a novel operational definition. The operational definition was developed using Poisson regression to identify clinical encounters indicative of
long COVID from a sample of negative and positive COVID-19 cases matched on
time-varying propensity to test positive for
SARS-CoV-2. Possible
risk factors for
long COVID were identified by stratifying descriptive
statistics by
long COVID status.
Findings:
Of 4,676,390 participants, 81,219 (1.7%) were identified as having
long COVID. Clinical
codes identified the fewest cases (n = 1,092, 0.02%), followed by free text (n = 8,368, 0.2%), sick notes (n = 14,469, 0.3%), and the operational definition (n = 64,193, 1.4%). There was limited overlap in cases identified by the
measures; however, temporal
trends and
patient characteristics were consistent across
measures. Compared with the general
population, a higher proportion of people with
long COVID were
female (65.1% versus 50.4%),
aged 38-67 (63.7% versus 48.9%),
overweight or obese (45.7% versus 29.4%), had one or more comorbidities (52.7% versus 36.0%), were immunosuppressed (6.9% versus 3.2%), shielding (7.9% versus 3.4%), or hospitalised within 28 days of testing positive (8.8% versus 3.3%%), and had tested positive before Omicron became the dominant variant (44.9% versus 35.9%). The operational definition identified
long COVID cases with combinations of clinical encounters (from four symptoms, six investigation types, and seven management
strategies) recorded in EHRs within 4-26 weeks of a positive
SARS-CoV-2 test. These combinations were significantly (p < 0.0001) more prevalent in positive COVID-19
patients than in matched negative controls. In a case-crossover
analysis, 16.4% of those identified by the operational definition had
similar healthcare patterns recorded before testing positive.
Interpretation:
The
prevalence of
long COVID presenting in
general practice was estimated to be 0.02-1.7%, depending on the
measure used. Due to challenges in diagnosing
long COVID and inconsistent recording of information in EHRs, the true
prevalence of
long COVID is likely to be higher. The operational definition provided a novel approach but relied on a restricted set of symptoms and may misclassify individuals with pre-existing
health conditions. Further
research is needed to refine and validate this approach.
Funding:
Chief Scientist Office (
Scotland),
Medical Research Council, and BREATHE.