Background: Post-COVID conditions (PCC), or “long COVID”, refers to the wide range of health consequences after recovery from acute SARS-CoV-2 infection. There is a lack of consensus on how PCC is defined.
Objectives: To directly measure changes in symptomatology before and after a COVID episode, and compare the prevalence of new symptoms to age, calendar month and propensity-score matched non-COVID comparators to create a data-driven definition of PCC.
Methods: We used the Optum® de-identified Electronic Health Record (EHR) dataset to identify persons diagnosed with COVID (ICD-10-CM of U07.1 or positive polymerase chain reaction test) from April 1, 2020 through September 30, 2021. For each person with COVID, we selected up to 3 comparators within 1 year of age, with a non-COVID health system encounter in the same month, and with a similar risk profile (using a propensity score with caliper of 0.1 standard deviations). People were followed for up to 365 days after index. ICD-10-CM diagnosis codes in the EHR present after index that were not present pre-index were compared between the COVID and comparator groups. The final COVID symptom score was computed as the sum of the new diagnoses weighted by each diagnosis’ ratio of prevalence in the COVID group relative to the control group. The weighted sum resulted in a scalar value, which was dichotomized: values 1 indicated PCC while < 1 indicated the absence of PCC. For the subset of COVID cases diagnosed in September 2021, we compared the incidence of PCC using our data-driven definition with the ICD-10-CM code U09.9 “Post-COVID Conditions”, which was first available for use in the US in October 2021.
Results: The final cohort contained 588,611 people with COVID and 1,286,050 comparators. Our definition identified 20% of persons as developing PCC in follow-up. PCC incidence increased with age: 7.8% of persons aged 0-17, 17.3% aged 18-64, and 33.3% aged 65 or older developed PCC. PCC did not change over time (20.0% among persons diagnosed with COVID in 2020 versus 20.3% among persons diagnosed with COVID in 2021). For COVID cases diagnosed in September 2021, our definition identified 19.0% with PCC in follow-up as compared to 2.9% with a U09.9 code in follow-up. More than half of persons with U09.9 codes did not have an additional specific symptom recorded, such as loss of taste or persistent cough.
Conclusions: Symptom and U09.9 code-based definitions alone captured different populations, and maximal capture may consider a combined approach. An algorithmic definition may provide greater sensitivity for identifying patients who may be suffering from PCC and for measuring the true burden of disease, particularly before the availability and routine utilization of specific ICD-10 codes and with the lack consensus-based definitions on the syndrome.
