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COVID-19 research briefs: 44% of secondary infections of SARS-CoV2 occur when the index case is presymptomatic
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. 4
Reference
Study design: Not applicable
Funding:
Setting: Not applicable
Synopsis
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.
Reviewer
Henry C. Barry, MD, MS
Professor
Michigan State University
East Lansing, MI
Comments
incubation period vs ore-symptomatic period
It would have been help to note how the researchers calculated the incubation period and what definition they used to separate these terms.They stated “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..”.
Current assumptions are an IP OF 2-14 days, which may mean you are infectious while in the IP phase —which is not uncommon but alarming for prevention through temperature and screening questions. Hence the push for physical distancing, masks and hand washing. 🍀