Both viral load and the duration of viral shedding of COVID-19 have a significant impact on disease transmission.
Early data have suggested that peak COVID-19 viral load occurs at the time of symptom onset although viral shedding can persist much longer.
Nevertheless, there is considerably heterogeneity in studies with some suggesting that viral shedding continues much longer after the initial acute illness. There is also a lack of data concerning how both viral load and shedding relate to factors such as age and disease severity.
In an effort to gain a better understanding of viral load kinetics, a team from the Division of Infection and Global Health Research, University of St Andrews, Fife, UK, conducted a systematic review in order to characterise these factors for COVID-19 and compared the results with two other coronaviruses: SARS-CoV and Middle East respiratory syndrome (MERS-CoV).
The systematic search identified 79 relevant studies with 5340 participants on COVID-19, 8 studies (1858 participants) on SARS-CoV and 11 studies (799 participants) on MERS-CoV. Analysis of the data revealed how the mean duration of RNA viral shedding for COVID-19 varied considerably depending on the part of the body tested. For example, the average shedding time was 17 days in the upper respiratory tract (maximum 83 days), 14.6 days in the lower respiratory tract (maximum 59 days), 17.2 days in stool samples (maximum 126 days) and 16.6 days in serum samples (maximum 60 days). Viable COVID-19 levels peaked within the first week of infection and but could not be detected after 9 days of illness. In contrast, for SARS-CoV and MERS-CoV, viable virus levels peaked after 10 -14 days and 7 – 10 days respectively although the authors were unable to detect a consistent relationship between viral shedding and disease severity for COVID-19. There was a positive and significant association between the duration of shedding and age (p = 0.0016) but not sex (p = 0.28).
In discussing these findings, the authors concluded that while viral particles continue to be shed for extended periods of time, the presence of viable COVID-19 virus is short-lived and suggested that isolation should commence at the first onset of symptoms.
Citation Cevik M et al. SARS-CoV-2, SARS-Co-V and MERS-CoV viral load dynamics, duration of viral shedding, and infectiousness: a systematic review and meta-analysis. Lancet Microbe 2020 https://doi.org/10.1016/S2666-5247(20)30172-5