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26th November 2020
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
23rd October 2020
This information is also important to inform the requirements for in-patient and outpatient isolation and it is necessary to gain a better insight of the potential significance of positive PCR tests over longer periods of time. Now researchers from the Division of Infectious Diseases, Oregon University, have undertaken a review of published data to determine the duration of viral shedding among those infected with COVID-19 and their findings have implications for the risk of transmission. The team queries public databases including PubMed, LitCoVID, the WHO COVID-19 literature repository and Google scholar for relevant articles. In each case, the articles were reviewed and assessed in terms of the design, population, healthcare setting, diagnostic testing methods and patient symptoms and illness severity.
A total of 77 studies were eligible for analysis and included prospective case studies, retrospective series, case reports, point prevalence studies and position statements. Only 59 studies were peer-reviewed, 6 were pre-prints and 13 researcher letters or a letter to the editor of a journal and 70 of the studies described hospitalised patients. All of the studies reported PCR-based assessment of viral shedding and 12 studies reported viral culture data. In terms of viral shedding, the data revealed that the duration ranged from a minimum of 1 day to 83 days although the pooled median duration of RNA shedding from respiratory samples based on 28 studies was 18.4 days (95% CI 15.5–21.3 days). When stratifying by disease severity, the median duration of RNA shedding was 17.2 days (95% CI 14–20.5 days) for those with mild to moderate disease and 19.8 days (95% CI 16.2–23.5 days) for those with severe disease. In general terms, the authors found that viral loads were highest within 1–2 weeks of illness onset but declined gradually although this rarely extended past 25 days. In discussing their results, the authors noted that while PCR positive tests can be prolonged, viral culture data suggested that viable virus samples could only be obtained from between 6 days prior to symptom onset but no later than 20 days after.
Fontana L et al. Understanding viral shedding of SARS-CoV-2: review of current literature. Infect Control Hosp Epidemiol 2020;1-35. doi:10.1017/ice.2020.1273