Viral Shedding in COVID 19 Patients

By Anders Gundersen, HGHI | March 10, 2020

Throat swabs are sufficient for testing, and a patient’s viral load is highest 1-5 days after the onset of symptoms: Researchers in Germany identified important aspects of how the novel coronavirus behaves. While the work is under peer-review, early publication provides details that can inform decisions on patient care, isolation, and discharge management.

Disclaimer: This article is available online pre-print and has not yet undergone the peer review process. The final version may therefore be slightly different than the version used to create this summary.

Virological assessment of hospitalized cases of coronavirus disease 2019

medRxiv | W├Âlfel, Corman, Guggemos et al. | Mar. 5, 2020

Using samples from 9 young-to-middle-aged patients who tested positive for SARS-CoV-2 from a hospital in Munich, Germany, two research groups in conjunction aimed to describe the virology, specifically body site-specific virus replication, immunity, and infectivity. It is worth noting that all of the patients examined presented with mild symptoms. Only two showed any signs of pneumonia.

This study provides some critical information on the behavior of the virus that can be used to inform decisions on patient care, isolation, and discharge management.

A series of questions were tested relating to the above three categories. Below is a list of some of the key questions and the answers that were obtained from the results from the experiments.

  1. Was there a difference in viral load between the different throat swab sites?
    • No.
    • Throat swabs are sensitive enough for diagnosis.
  2. Did the viral load (amount of virus in a sample) vary over the course of the infection?
    • Viral load was highest between days 1-5 after the onset of symptoms, lower after day 5, and lower still on day 22.
  3. Did different sample sites show different viral shedding (reproductive) behavior?
    • It varied.
    • Sputum samples and swab samples were mostly similar, but with some variation between patients.
    • The viral load in sputum samples declined more slowly.
    • Viral shedding in the upper respiratory tract appeared to be declining when the patients were first tested, but viral shedding in sputum lasted through the first week of symptoms, indicating more efficient transmission than SARS through active pharyngeal shedding even when symptoms are still mild.
    • The prolonged viral shedding (reproduction) in sputum supports further home isolation of patients who are discharged from the hospital.
  4. How infective was the virus over the course of the illness?
    • More infective at the beginning (first week) and less infective toward the end. Isolating the virus was most successful from sputum samples and entirely unsuccessful from stool samples (perhaps due to the mild nature of the cases).
    • After illness day 8, isolation was unsuccessful, indicating that transmission is unlikely after approximately 8-10 days of illness, but perhaps longer if the cases are more severe.
  5. Did the virus actively replicate? Where in the body and for how long?
    • Active replication occurred in the throat up to illness day 5 according to sputum and swab samples. There was evidence of active replication in the gastrointestinal tract as well.

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