SARS-CoV-2 RNA Viral Load Dynamics and Duration of Shedding

According to a meta-analysis of studies regarding coronavirus viral kinetics, SARS-CoV-2 RNA shedding can be prolonged but the duration of viable virus is relatively short. The results of this review of studies reporting on SARS-CoV-2, SARS-CoV, or MERS-CoV infection were published in The Lancet Microbe.

Investigators analyzed 79 SARS-CoV-2 studies with 5340 individuals, 8 SARS-CoV studies with 1858 individuals, and 11 MERS-CoV studies with 799 individuals.

Of the 79 studies about SARS-CoV-2, 61 reported maximum or median viral RNA shedding in at least 1 bodily fluid and 6 provided duration of shedding stratified by illness severity. Mean viral shedding duration was 17.0 days (95% CI, 15.5-18.6) in the upper respiratory tract and 14.6 days (95% CI, 9.3-20.0) in the lower respiratory tract. In stool samples, duration was 17.2 days (95% CI, 14.4-20.1) and in serum samples, duration was 16.6 days (95% CI, 3.6-29.7).

Investigators found that maximum duration of RNA shedding reported in the upper and lower respiratory tract was 83 and 59 days, respectively. For stool samples and serum samples, duration of shedding was 126 and 60 days, respectively. Studies reporting shedding in both the upper respiratory tract and stool samples were used to calculate pooled mean viral shedding duration and this was positively associated with age (slope 0.304; 95% CI, 0.115–0.493; P=.0016), however, there was no association with sex (P=.28).

Viral load in the upper respiratory tract appeared to peak in the first week of illness; the highest loads were observed at days 3 to 5 of illness or soon after symptom onset, and then loads consistently declined. The peak viral load for the lower respiratory tract occurred in the second week of illness.

For SARS-CoV and MERS-CoV, peak viral load in the upper respiratory tract occurred at days 10 to 14 and days 7 to 10, respectively. The shedding duration of SARS-CoV-2 varied based on disease severity; 13 of 20 studies found longer duration of shedding in patients with severe illness compared to nonsevere illness. However, 5 studies involving upper respiratory tract samples and 1 involving stool samples found similar shedding durations independent of disease severity.

Shedding dynamics may have been modified by the variety of treatments administered in different studies. Further study limitations included substantial study heterogeneity and that the true clinical infectious shedding window might not align with culture duration.

“[D]espite evidence of prolonged RNA shedding in SARS-CoV-2 patients, viable virus appears to be short lived,” investigators concluded. High titers are detected early in disease course and a peak is observable at symptom onset to day 5 of illness. According to investigators, these findings emphasize the importance of early case detection and isolation and the need for public education on the spectrum of illness. Investigators recommend that isolation should begin at the start of first symptoms, including mild and atypical symptoms that can precede the typical cough and fever associated with COVID-19.

Reference

Cevik M, Tate M, Lloyd O, Maraolo AE, Schafers J, Ho A. SARS-CoV-2, SARS-CoV, and MERS-CoV viral load dynamics, duration of viral shedding, and infectiousness: a systematic review and meta-analysis. Lancet Microbe. Published online November 19, 2020. doi:10.1016/S2666-5247(20)30172-5