1. Those testing positive for COVID-19 and experiencing five or more symptoms during the first week had greater odds of having a symptom duration longer than 28 days (long COVID).
2. The most predictive symptoms of long COVID were fatigue, headache, dyspnea, hoarse voice, and myalgia.
3. Among individuals ≥70 years of age, anosmia was the strongest predictor of long COVID.
Evidence Rating Level: 3 (Average)
The effects of COVID-19 are being studied in great detail to determine the risk factors of serious illness and death. One heterogeneous factor in COVID-19 is symptom duration, which is underrepresented in research among the general population. The term ‘long COVID’ (LC28) has been defined as symptoms persisting for over 28 days while ‘short COVID’ refers to less than 10 days. This prospective observational cohort study of COVID-19 symptoms used data from users of the COVID Symptom Study. These individuals reported testing positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and used the app to report when their symptoms subsided. These participants were then compared to symptomatic, SARS-CoV-2-negative controls matched for age, sex, and body mass index (BMI). Between March 24, 2020 and September 2020, 4,223,955 adults registered with the app (M [SD] age = 45.97 [15.8] years, 57% female, 88.2% United Kingdom). A total of 4,182 participants testing positive met eligibility criteria and were included in subsequent analyses with their matched controls. A total of 13.3% reported LC28, 4.5% reported symptoms for ≥8 weeks, and 2.3% reported symptoms for >12 weeks. LC28 was commonly associated with headache (OR = 2.62, 95% CI 2.04 to 3.37), fatigue (OR = 2.83, 95% CI 2.09 to 3.83), myalgia (OR = 2.22, 95% CI 1.80 to 2.73), hoarse voice (OR = 2.33, 95% CI 1.88 to 2.90), and dyspnea (OR = 2.36, 95% CI 1.91 to 2.91), exacerbated by older age, female sex, and elevated BMI. LC28 was associated with experiencing more than five symptoms in the first week of illness (OR = 3.53, 95% CI 2.76 to 4.50). In older adults (≥70 years), anosmia was the most predictive symptom of LC28 (OR 7.35, 95% CI 1.58 to 34.22). Those with LC28 were also more likely to report symptom relapses than those with a duration of <28 days (p < 0.0005). Investigators then used a simple model to determine the differences between short and long COVID at 7 days (n = 2,149). This model showed an area under the curve of the receiver operating characteristic curve of 76%, such that it could be utilized to identify symptomatic patients at risk for long COVID. Overall, this study suggests specific symptoms associated with long COVID and has demonstrated risk factors as well as the ability to predict who may be at greatest risk based on symptom duration. This information could guide clinical decisions for prevention and treatment of adults at risk for COVID-19.
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