Viral Load Dynamics, Duration of Viral Shedding, Infectiousness of the Various SARS Viruses Looking at SARS-CoV-2, SARS-CoV, and MERS-CoV. How Infectious Are They?

This is a systematic review and meta-analysis published in The Lancet November 19 by Cevik and others.

At last some research looking into the viral load kinetics and duration of viral shedding to determine disease transmission of these viruses.

The authors aimed to characterise viral load dynamics, duration of viral RNA shedding, and viable virus shedding of SARS-CoV-2 in various body fluids and to compare SARS-CoV-2 with SARS-CoV and MERS-CoV viral dynamics.
In their review, they searched databases for research articles published between January 1, 2003 and June 6, 2020.

They included case series, cohort studies and randomised control trials that reported SARS-CoV-2, SARS-CoV, or MERS-CoV infection, and reported viral load kinetics, duration of viral shedding, or viable virus.

They calculated the mean duration of viral shedding in 95% CTs for every study included and apply the random effects model to estimate a pooled effect size. They awaited meta regression to help assess the effect of potential moderators on the pooled effect size.

They found that from 79 studies, that is 5340 individuals on SARS-CoV-2, eight studies that is 1858 individuals on SARS-CoV and 11 studies that 799 individuals on MERS-CoV were able to be included.

Mean duration of SARS-CoV-2 RNA shedding was 17 days in the upper respiratory tract, 14.6 days in the lower respiratory tract, 17.2 days in the stool and 16.6 days in serum samples.

Maximum shedding duration was 83 days in the upper respiratory tract, 59 days in the lower respiratory tract and 126 days in stools and 60 days in serum.

They also found that the pooled mean SARS-CoV-2 shedding duration was positively associated with age. The study detected live virus beyond day nine of illness, despite persistently high viral loads, which were inferred from cycle threshold values.

SARS-CoV-2 viral load in the upper respiratory tract appeared to peak in the first week of illness, whereas that of SARS-CoV peaked at days 10 to 14 and that a MERS-CoV peaks at days 7 to 10.

The interpretation from their study was that although SARS-CoV-2 RNA shedding in respiratory and stool samples can be prolonged, duration of the viable virus is relatively short lived.

SARS CoV-2 titres in the upper respiratory tract peak in the first week of illness.

RNA detection cannot be used to infer infectiousness. High titres of SARS-CoV-2 are detected early in the disease course, with an early peak observed at the time of symptom onset to day 5 of illness; this finding probably explains the efficient spread of SARS-CoV-2 compared with SARS-CoV and MERS-CoV.

This has important implications for SARS-CoV-2 transmission in the community and hospital setting, emphasising the importance of early case finding and prompt isolation as well as public education about the spectrum of illness.
This study shows that isolation practices should be commenced with the start of first symptoms, which include mild and atypical symptoms, preceding typical symptoms of COVID-19 such as cough and fever.

However, given the potential delays in isolation of patients, even the early detection and isolation strategy might not be fully effective in containing SARS-CoV-2. The London General Practice is excited by this study and hopefully this will help to form the basis for an effective quarantining and isolation period following infection with SARS-CoV-2 virus.

Dr Paul Ettlinger
The London General Practice

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