Presymptomatic transmission of COVID-19 is substantial: data from China

  • He X & al.
  • Nat Med
  • 15 Apr 2020

  • curated by Miriam Davis, PhD
  • Clinical Essentials
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Takeaway

  • COVID-19 transmission is estimated to start at least 2 days before symptom onset, based on viral shedding and epidemiological data from China.
  • 44% of disease transmission is estimated to be presymptomatic.
  • Infectiousness may decline abruptly at about 1 week.

Why this matters

  • This substantial level of presymptomatic transmission far exceeds the rate of 6% reported for Singapore.
  • These findings suggest a need for shifts in disease-control measures, including contact tracing, to 2-3 days before symptom onset.

Study design

  • Temporal patterns of viral shedding were determined based on viral load clinical data for 94 patients with laboratory-confirmed COVID-19.
  • Viral load data were combined with epidemiological data from 77 transmission pairs (one person likely infected the other) on incubation period and serial interval between cases in the transmission chain.
  • Funding: Department of Science and Technology of Guangdong Province; other.

Key results

  • Infectiousness (using viral load data) began 2.3 days and peaked 0.7 days before symptom onset.
  • Infectiousness was estimated to decline abruptly within 7 days.
  • Presymptomatic transmission accounted for 44% of transmissions.
  • Viral load data did not vary by sex, age group, or disease severity.

Limitations

  • Potential for recall bias.
  • Small sample size.