- There is evidence that supports that transmission of SARS-CoV-2 can occur before a patient becomes symptomatic.
- The duration of transmissibility while patients are presymptomatic has not been clearly established.
- The possibility of presymptomatic transmission reinforces the importance of social distancing measures and suggests that symptom-based control strategies are insufficient.
- If control measures are not enforced, asymptomatic patients can potentially lead to significant viral transmission and even local outbreaks.
The data comes from 4 articles.
Wycliffe W. et al present an epidemiological investigation of all the confirmed cases of SARS-CoV-2 in Singapore from January 23, 2020 to March 16, 2020. In total, 243 cases were investigated to determine whether presymptomatic transmission could have occurred.
Arons M. et al present a study accessing the transmission in a nursing facility in King County, Washington after a first case positive case was identified. All 116 residents and symptomatic staff members were testing using real-time RT-PCR at two different points in time.
Sun T., & Weng D. use a modeling-based approach with data from the Jiangsu and Anhui provinces in China collected from January 23 to March 31. Their goal was to determine the impact of asymptomatic and imported cases on the viral transmission.
Cheng H. et al present a study of the transmission dynamics of COVID-19. They enrolled 100 confirmed cases in Taiwan and use contract tracing to find 2761 of their close contacts from January 15 to March 18, 2020. Contacts were followed up to 14 days after the last exposure to the confirmed case
- Wycliffe W., Li Z.,Chiew C., et al (April 1, 2020). Presymptomatic Transmission of SARS-CoV-2 — Singapore, January 23–March 16, 2020. Centers for Disease Control and Prevention. http://dx.doi.org/10.15585/mmwr.mm6914e1.
- Arons, M., Hatfield, K. M., et al (2020). Presymptomatic SARS-CoV-2 Infections and Transmission in a Skilled Nursing Facility. The New England Journal of Medicine. http://dx.doi.org/10.1056/nejmoa2008457.
- Sun T., & Weng D. (April 24, 2020). Estimating the Effects of Asymptomatic and Imported Patients on COVID‐19 Epidemic Using Mathematical Modeling. Journal of Medical Virology. https://doi.org/10.1002/jmv.25939.
- Cheng H., Jian S., Liu, D. al (May 1, 2020). Contact Tracing Assessment of COVID-19 Transmission Dynamics in Taiwan and Risk at Different Exposure Periods Before and After Symptom Onset. JAMA Intern Med. https://doi.org/10.1001/jamainternmed.2020.2020 .