Forty-Four Percent of SARS-CoV-2 Transmission May Occur Prior to Symptom Onset
Douglas K. Rex, MD, FASGE, reviewing He X, et al. medRXiv 2020 Mar 18.
In a Chinese study of 77 infector-infectee pairs (clear viral transmission from one individual to the other) that was not peer reviewed, investigators used viral loads at various time points to estimate the course of infectiousness. Using an estimated mean incubation period of 5.2 days (from a different study), they inferred that infectiousness started 2.5 days before symptom onset and peaked at 0.6 days after symptom onset. The fraction of viral transmission occurring before the infectors had developed any symptoms was estimated at 44%.
COMMENT
If true, this is bad news. From a public health perspective, it suggests that contact tracing and isolation will be ineffective in controlling the epidemic, and that control will have to rely on effective hygiene and social isolation. From the endoscopist perspective, it means that previous classifications of patients as low risk (no symptoms and no exposure or high-risk travel) or high risk (known infection, symptoms, or exposure) may not be a valid way of guiding measures for protection of endoscopy staff. Perhaps all endoscopy patients should be treated as high risk.
Note to readers: At the time we reviewed this paper, its publisher noted that it was not in final form and that subsequent changes might be made.
Douglas K. Rex, MD, FASGE
CITATION(S)
He X, Lau EHY, Wu P, et al. Temporal dynamics in viral shedding and transmissibility of COVID-19. medRXiv 2020 Mar 18. (Epub ahead of print) (https://doi.org/10.1101/2020.03.15.20036707)
