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SARS-CoV-2 viral load in the upper respiratory tract of children and adults with early acute COVID-19

Our take —

This single-center study with a fairly small sample size showed similar quantities of detectable SARS-CoV-2 RNA from nasopharyngeal swabs across age groups, including children. However, some cautions apply: 1) all patients were symptomatic, and results are not representative of all infections; 2) the authors did not consider any other differences between patients that might affect viral loads; and 3) the relationship between viral loads and actual transmissibility of SARS-CoV-2 is unclear.

Study design

Case Series

Study population and setting

This study quantified SARS-CoV-2 viral load among symptomatic adults 16 years and older (n=352) and children (n=53) COVID-19 at a single hospital in Geneva, Switzerland between March 10 and May 26, 2020. Included patients had RT-PCR confirmed SARS-CoV-2 infection, had no prior positive SARS-CoV-2 test, and presented within n 5 days of symptom onset. Nasopharyngeal swab samples were tested with either the Cobas 6800 SARS-CoV-2 RT PCR or the Charité E gene assay (in-house). Viral loads on the log10 scale were calculated using formulas with cycle thresholds (Cobas: [CT-44.5]/-3.3372; Charité: [CT-41.7]/-3.4529). Age was both treated as continuous and categorized as “child” (0-11 years), “adolescent” (12-19 years), “young adult” (20-45 years), and “older adult” (>45 years). Associations between age and viral load were assessed via Pearson’s correlation coefficient and one-way ANOVA.

Summary of Main Findings

The mean viral load (in log10 copies of RNA/mL) was 6.0 for children, 5.9 for adolescents, 5.9 for young adults, and 6.4 for older adults. Continuous age and viral load were not correlated (r=0.01, p=0.80). Categorical age and viral load were not associated in ANOVA (p=0.26). No Bonferroni-adjusted pairwise comparisons between age categories were statistically significant.

Study Strengths

The study restricted patients to those presenting within 5 days of symptom onset.


The sample size was small, particularly for children, and the study population was limited to a single center. The study only included symptomatic patients presenting at hospital; if symptom severity is correlated with viral shedding and age, then results may not be representative of all SARS-CoV-2 infections. There were extremely limited data presented on patient covariates and distributions of viral load. No information was presented on symptom profile, disease severity, or stage of illness. No potential confounders were assessed. The relationship between viral shedding and infectiousness is unclear.

Value added

Few studies have directly compared the quantity of detectable SARS-CoV-2 RNA in samples from children and adults.

This review was posted on: 9 October 2020