Viral load dynamics and disease severity in patients infected with SARS-CoV-2 in Zhejiang province, China, January-March 2020: retrospective cohort study

Epidemiology InfectiologyVirology
Zheng S et al

Main result

A total of 96 patients included representing 3497 samples.

iral RNA was present in 59% of stool and 41% of serum samples. The urine sample from one patient was positive for SARS-CoV-2. The median duration of virus in stool (22 days, interquartile range 17-31 days) was significantly longer than in respiratory (18 days, 13-29 days; P=0.02) and serum samples (16 days, 11-21 days; P<0.001). 

The median duration of virus in the respiratory samples of patients with severe disease (21 days, 14-30 days) was significantly longer than in patients with mild disease (14 days, 10-21 days; P=0.04). In the mild group, the viral loads peaked in respiratory samples in the second week from disease onset, whereas viral load continued to be high during the third week in the severe group.


The duration of SARS-CoV-2 is significantly longer in stool samples than in respiratory and serum samples.

The virus persists longer with higher load and peaks later in the respiratory tissue of patients with severe disease.

Strength of evidence Weak

- Monocentric retrospective cohort study
- Small number of patients (n=96)
- Selection bias by only taking samples from patients staying in the hospital
- Viral load dependent on the quality of the sample collection
- PCR does not distinguish between viable and non-viable viruses.


To evaluate viral loads at different stages of disease progression in patients infected with the 2019 severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) during the first four months of the epidemic in Zhejiang province, China.


Retrospective cohort study of patients with laboratory confirmed covid-19 admitted consecutively to the First Affiliated Hospital, College of Medicine, Zhejiang University from 19 January 2020 to 15 February 2020.

SARS-CoV-2 RNA was measured by qRT-PCR in serum, respiratory (sputum or saliva after deep cough), stool, and urine samples

Epidemiological, clinical, and laboratory characteristics and treatment and outcomes data were obtained through data collection forms from hospital electronic medical records.

The severity of illness was evaluated according to the Guideline for Diagnosis and Treatment of SARS-CoV-2 issued by the National Health Commission of the People’s Republic of China.

Patients who test negative for SARS-CoV-2 for two consecutive days in respiratory samples were considered to be clear of infection.


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