- Document Type
- Rapid Review
- Review Code
- EPM210601v2 RR
- Question Submitted
- June 22, 2021
- Date Completed
- March 31, 2022
- Status
- 3. Completed
- Research Team
- Epidemiology & Modelling
- Document Type
- Rapid Review
- Review Code
- EPM210601v2 RR
- Question Submitted
- June 22, 2021
- Date Completed
- March 31, 2022
- Status
- 3. Completed
- Research Team
- Epidemiology & Modelling
- Updated Key Findings
- March 31, 2022
- Since the previous rapid review, a large amount of new research and reviews are available to draw upon. Many studies have addressed aspects previously identified as limitations such as the use of validated questionnaires, documenting pre-COVID health status, and control cohorts. Many studies now include only participants with RT-PCR verified infections and also focus on a range of disease severities from severe (hospitalized) to mild (managed in the community); PCR-validated infections ensure a higher quality of comparison between test-positive and control groups. Studies involving control groups contributed illuminating findings about prevalence and incidence of long COVID, which is lower than previous thought when compared to control groups. Comorbidities/factors that potentially indicate increased risk of developing long COVID-19 have been identified and widely agreed-upon, such as diabetes, cardiovascular diseases, obesity, and gender (female).
- A case definition for long COVID has yet to be adopted but is commonly defined as COVID-related symptoms that persist or emerge beyond 4 weeks of infection with two subsequent phases: “ongoing symptomatic COVID-19 (OSC; signs and symptoms from 4 to 12 weeks from initial infection) and 2) post-COVID-19 syndrome (PCS; signs and symptoms beyond 12 weeks) with respect to symptomatology, abnormal functioning, psychological burden, and quality of life”. Long COVID includes both OSC and PCS.
- It is estimated that 32% of non-hospitalized and 51% of hospitalized people experience Long COVID symptoms within 12 weeks of infection; however, higher estimates up to 92% have been reported in studies with a greater proportion in persons who were previously hospitalized. More than 200 symptoms affecting 10 organ systems have been identified in various reports or systematic reviews. Many patients (49%), experience at least one COVID-related symptom 12 months after infection (compared to 68% at 6 months).
- For many persons, symptoms improve over time while others experience persistent and/or new symptoms. At 3 months post-infection the most frequently reported symptoms are fatigue (up to 98%), dyspnoea (up to 88%), headache (up to 91%) and taste/smell disorders (up to 58%).
- Mechanism(s) leading to long COVID remain unclear, but these comorbidities/factors have been found to indicate potentially increased risk of developing long COVID:
o Age (60+)
o Greater number of symptoms during the acute phase of illness (typically 5+)
o Manifestation of specific symptoms
o Diabetes
o Cardiovascular disease
o Obesity or high BMI
o Gender (female)
- There is limited evidence to support the contention that vaccination lowers incidence of long COVID.
- Key Findings
- July 9, 2021
- The frequency of Long COVID symptoms varies widely across studies based on populations studied, duration of follow up and methods of assessment of symptoms.
- It is estimated that 1 in 50 persons experience Long COVID symptoms after 12 weeks; however, higher estimates up to 80% have been reported in studies with a greater proportion of persons who were previously hospitalized. A recent study of a mixed cohort of 96 persons found that only 22.9% had no symptoms at 12 months post diagnosis.
- A wide range of symptoms affecting multiple organ systems has been reported. For many persons symptoms improve over time while others experience persistent and/or new symptoms. Among studies with the longest duration of follow up, the most frequently reported symptoms included fatigue (up to 65%), dyspnea (up to 50%), headache (up to 45%), anosmia/ageusia (up to 25%), cognitive memory/concentration (up to 39.6%) and sleep disorders (up to 26%).
- Few studies estimated the duration of symptoms with estimates ranging from 2.2% for 6 months and 27% for 7-9 months.
- The mechanism(s) leading to Long COVID remain unclear but those experiencing post acute sequelae tend to be older, have a greater number of symptoms during the acute phase of illness or manifest specific symptoms and live with multiple comorbid conditions such as obesity.
- The lack of consensus on a definition of Long COVID contributes to marked variations in robust prevalence estimates.
- Notes
- A significant amount of evidence was produced since the previous review. This updated review was rewritten with extensive changes which have not been identified in red.
- Category
- Clinical Presentation
- Epidemiology
- Subject
- Long Covid
- Symptoms
- Clinical Presentation
- Population
- All
- Clinical Setting
- Ambulatory
- Community
- ICU
- Long Term Care
- Medicine Unit
- Primary care
- Public Health
- Priority Level
- Level 1 2-3 days
- Cite As
- Hammond, B; Badea, A; Groot, G; Reeder, B; Howell-Spooner, B; Mueller, M. What is the incidence and duration of long COVID cases? 2022 Mar 31, Document no.: EPM210601v2 RR. In: COVID-19 Rapid Evidence Reviews [Internet]. SK: SK COVID Evidence Support Team, c2022. 18 p. (CEST rapid review report).
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