Differences of SARS-CoV-2 Shedding Duration in Sputum and Nasopharyngeal Swab Specimens Among Adult Inpatients With COVID-19

Diagnostic InfectiologyVirology
Wang K et al

Main result

Study of 68 inpatients (intensive and sub-intensive care units): 36 (52.9%) men and 32 (47.1%) women, mean age 67 years (IQR: 57-72), 39 (57.4%) patients with comorbidities (17.6% with chronic lung disease, 17.6% with type II diabetes and 13.2% with heart disease).

At admission: 43 (63.2%) patients with positive nasopharyngeal sample and 25 (36.8%) with positive expectoration.

During hospitalization: 49 (72.1%) patients with positive nasopharyngeal sample, 14 (20.6%) patients with negative nasopharyngeal sample but positive expectoration, and 5 (7.4%) patients with positive sputum at admission but both tests were negative during hospitalization.

Of the 16 patients positive for both admission tests, 9 were still positive for sputum after becoming negative for the nasopharyngeal sample.

The mean duration of viral shedding was 19 days (IQR: 14-25, p<0.001) for nasopharyngeal sampling, 34 days (IQR: 24-40, p<0.001) for sputum sampling, and 21 days (IQR: 16-31) for both methods combined.

Among the risk factors considered, chronic lung disease and corticosteroid therapy were statistically correlated with nasopharyngeal smear positivity, and type II diabetes correlated with sputum positivity.

Age stratified analyses showed that age ≥65 years was a risk factor for prolonged excretion (HR 1.71; 95% CI: 1.12-2.93, p<0.01).


The mean duration of viral excretion is 21 days considering both methods of sampling, but the duration of excretion is significantly longer in sputum (34 days; IQR: 24-40, p<0.001).

It is important to note that 9 of the 16 patients who tested positive for both tests at admission, still had positive sputum after negative nasopharyngeal swab.

Among the comorbidities studied, chronic lung disease and corticosteroid therapy were associated with positive nasopharyngeal samples and type II diabetes was associated with positive both methods.

The study also showed that age ≥ 65 years was a risk factor for prolonged excretion (HR 1.71; 95% CI: 1.12-2.93, p<0.01).

Strength of evidence Weak

- pre-proof article- small sample (n= 68 patients)
- methodology: possible inter-individual difference between the performers of the samples, absence of detection of IgG and IgM antibodies on the serum, methods of analysis different from the two types of sample.


To determine the duration of SARS-CoV-2 excretion in the upper and lower airways and the associated risk factors.


Prospective multicenter Chinese cohort study.

68 COVID-19 patients included between February 10 and March 20, 2020 at Wuhan Taikang Tongji Hospital and Huoshenshan Hospital (China).

Nasopharyngeal and sputum samples were collected every 1 to 2 days for all patients until two consecutive negative tests were obtained (nasopharyngeal sample assessed by RT-PCR and sputum sample assessed by screening for IgM and IgG antibodies to SARS-CoV-2).

The time between the onset of symptoms and the negativity of the two consecutive tests was considered to be the period of viral shedding.
Several potential risk factors for prolonged viral shedding were evaluated: sex, age, comorbidities, lymphocyte counts, and corticosteroid therapy.

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