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Observational cohort study of long COVID amongst 2 million elderly adults

Observational cohort study of long COVID amongst 2 million elderly adults

In a recent study published within the journal PLoS Medicine, researchers investigated whether COVID-19 patients could fit the diagnostic criteria for long coronavirus disease (COVID-19) or post-COVID condition (PCC) after a bout of influenza (a condition known as long Flu).

Study: Prevalence and characteristics of long COVID in elderly patients: An observational cohort study of over 2 million adults within the US. Image Credit: p.unwell.i / Shutterstock


There have been wide variations within the reported incidence of PCC resulting from differences within the definition and measurement methods. PCC might be underreported amongst elderly individuals probably resulting from their lower likelihood of responding to surveys and their symptoms often being masked by other chronic medical conditions. Comparing long flu and PCC could provide invaluable insights into the pathogenesis and treatment of PCC, a condition that is just not well-characterized to this point.

Multiple similarities exist between influenza and COVID-19. The 2 conditions have similar etiological agents, i.e., single-stranded ribonucleic acid (RNA) viruses with high affinity for respiratory organs, although generalized manifestations are observed. Each diseases are highly prevalent globally and have caused substantial socioeconomic and medical burdens. In light of the similarities between the 2 conditions, there might be symptomatic overlap between their post-infection syndromes.

In regards to the study

The current observational cohort study estimated long Flu and PCC incidence in Medicare-insured COVID-19 patients based on World Health Organization (WHO) criteria. In addition they compared the symptomatology and use of healthcare resources between long Flu and CC patients.

The study involved Medicare (medical insurance program of the US) beneficiaries aged >65 years, who were infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) between 1 April 2020 and 30 June 2021. De-identified records of the Medicare beneficiaries for the period between 2016 and 2021 were accessed through the Centres for Medicare and Medicaid Services (CMS) Virtual Research Data Centre (VRDC). The team used the international classification of diseases, tenth revision, and clinical modification (ICD-10)-CM diagnostic codes for evaluating influenza, COVID-19, and protracted symptoms.

PCC was defined based on the ICD-10 code for the condition, or the presence of any of the 11 WHO-defined PCC symptoms, after one to a few months of acute infection. The team identified Long Flu amongst influenza patients diagnosed in 2018-2019 using the PCC symptomatic definition (influenza comparator group). Long Flu and PCC were comparatively assessed regarding the following outcomes: (i) any-cause hospitalization; (ii) PCC symptom-associated hospitalization; (iii) emergency department (ED) visits for PCC symptoms; and (iv) PCC symptom-associated outpatient visits.

Data were adjusted for gender, age, region, race, Medicare-Medicaid eligibility, chronic comorbid conditions, and former yr hospitalizations. Multiple logistic-type and log-linear-type regression modeling analyses were performed to find out the percentages ratios (OR). The team excluded individuals with <12 months of Medicare insurance coverage and people with none health encounters within the yr before influenza or COVID-19 diagnosis. As well as, individuals who were continually enrolled in Medicare Advantage plans, most of which were of the private health maintenance organization (HMO) type, within the yr prior or 12.0 weeks post-influenza or COVID-19 diagnosis, have been excluded.


Out of two,071,532 participants who were followed up for 2 months, symptom-based PCC was identified amongst 29% (n=61,631) and 17% (n=246,154) of inpatients and outpatients, respectively. Nevertheless, the estimated rates using ICD-10 codes were considerably lower, i.e., 2.6% (n=5,521) for inpatients and 0.5% (n=7,213) for outpatients. Of 933,877 individuals with influenza, 25% (n=18,824) and 17% (n=138,951) of inpatients and outpatients, respectively, satisfied the definition of long Flu.

In comparison with individuals with long Flu, PCC patients had a greater incidence of fatigue, dyspnea, neurocognitive symptomatology, smell/taste loss, and palpitations. PCC outpatients had a greater likelihood of any-cause hospital admission (32%, n=74,854) vs. 27% (n=33,140), OR 1.1), and the next variety of outpatient encounters in comparison with long Flu patients visiting outpatient departments (2.90 vs. 2.50 visits, IRR 1.1). There have been fewer ED visits amongst PCC patients, likely resulting from lower ED use during COVID-19. Despite comparable overall incidence rates, PCC patients experienced notably different symptoms as compared to long Flu patients and had a greater likelihood of accessing outpatient and inpatient healthcare services.


Overall, the study findings showed that depending on particular PCC codes, underreporting might be considerable. PCC occurred in 17% and 29% of COVID-19 outpatients and inpatients, respectively, aged >65 years. The corresponding estimates for long Flu incidence, identified by similar symptoms in the course of the 2018 and 2019 pre-pandemic influenza seasons, were 17% and 25%, respectively.

Nevertheless, there have been noteworthy differences within the symptoms of the 2 conditions. Further, PCC was related to greater utilization of healthcare resources in comparison with long Flu, indicating a bigger impact on individual well-being and healthcare expenditures. The first study limitation was that the PCC diagnosis was not verified independently. Nevertheless, the researchers presented a way to operationalize the clinical definition of PCC by excluding individuals based on history alone (symptoms not occurring within the previous yr) or by history and comorbid conditions.

The exclusion by history alone approach yielded PCC estimates of 29% and 17% amongst inpatients and outpatients, respectively, in comparison with those published within the literature. The extra exclusion criteria of comorbidities significantly reduced PCC estimates to eight.80% and 5.70% for inpatients and outpatients, respectively. The comorbidity exclusion estimates seemed too stringent, given the prevalence of fibromyalgia with chronic pain and fatigue, cardiac failure, and chronic obstructive pulmonary disease amongst 54%, 43%, and 41% of the sample population, respectively.


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