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Symptoms before and after COVID-19: a population and case-control study using prospective data.

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Experiencing symptoms before COVID-19 increases the risk of prolonged illness. Many long COVID patients were asymptomatic before infection, but pre-existing symptoms significantly worsen outcomes.

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Area of Science:

  • Epidemiology
  • Infectious Diseases
  • Public Health

Background:

  • A significant number of individuals experience prolonged symptoms following acute coronavirus disease 2019 (COVID-19).
  • The influence of pre-infection symptoms on the duration of post-acute COVID illness remains an area of investigation.

Purpose of the Study:

  • To assess the impact of pre-infection symptoms on the duration and severity of post-acute COVID illness.
  • To identify risk factors associated with prolonged COVID-19 symptoms.

Main Methods:

  • Survival analysis of 23,452 adults with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, using data from the ZOE COVID Symptom Study app.
  • A case-control study matched 1:1 (n=1350 pairs) comparing individuals with long illness (≥8 weeks) versus short illness (<4 weeks), analyzing baseline symptoms (4-8 weeks pre-infection).

Main Results:

  • Individuals with pre-infection symptoms had a longer COVID-related symptom duration (median 15 days vs. 10 days).
  • Baseline fatigue nearly doubled symptom duration. Pre-infection symptoms doubled the odds of long illness (OR 2.14).
  • While many with long COVID were asymptomatic beforehand (67.4%), a significant proportion (32.6%) had baseline symptoms, compared to 18.9% in the short illness group (p<0.0001).

Conclusions:

  • Pre-existing symptoms before COVID-19 infection are associated with longer illness duration and increased odds of developing long COVID.
  • A substantial portion of individuals with long COVID were asymptomatic prior to SARS-CoV-2 infection, indicating other contributing factors.