COVID-19 research briefs: 44% of secondary infections of SARS-CoV2 occur when the index case is presymptomatic

Daily POEMs

Published: 2020-05-08 © 2020 John Wiley & Sons, Inc.

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Clinical question
How common is the presymptomatic transmission of the COVID-19 virus?

Bottom line
This analysis of the temporal pattern of viral shedding of COVID-19 finds that a high proportion of secondary cases were infected when the index case was presymptomatic. (LOE = 4)

He X, Lau EHY, Wu P, et al. Temporal dynamics in viral shedding and transmissibility of COVID-19. [published online ahead of print, 2020 Apr 15] Nat Med 2020;10.1038/s41591-020-0869-5. doi:10.1038/s41591-020-0869-5.

Study design: Not applicable

Setting: Not applicable

Research Brief #13: COVID-19 is highly contagious. Transmission during the presymptomatic and early symptom phases, such as occurs with the influenza virus, could make it difficult to institute effective quarantine procedures. These researchers from China studied the temporal pattern of viral shedding in 94 patients who tested positive for COVID, and they modeled viral shedding in another 77 infector-infectee transmission pairs. The 94 COVID-19 patients had a total of 414 throat cultures for COVID-19 from symptom onset to 32 days after onset. The greatest viral load shedding was at the time of symptom onset, and the authors surmise that infectiousness peaks at or before symptom onset. In the study of 77 infector-infectee pairs, based on epidemiologic modeling and a mean incubation period of 5.2 days, the authors inferred that infectiousness starts 2.3 days before symptom onset with a peak infectiousness at 0.7 days prior to symptom onset. They estimated that 44% of the secondary cases they studied were infected during the presymptomatic phase of the person who infected them. The researchers conclude that there is substantial presymptomatic transmission of COVID-19.

John Hickner, MD, MS
Professor Emeritus
Dept of Family Medicine
Michigan State University
East Lansing, MI

Copyright © 2020 John Wiley & Sons, Inc.