Inferring transmission risk of respiratory viral infection from the viral load kinetics of SARS-CoV-2, England, 2020 to 2021 and influenza A virus, Hong Kong, 2008 to 2012
Author(s)
Type
Journal Article
Abstract
Background
Infectiousness of respiratory viral infections is quantified as plaque forming units (PFU), requiring resource-intensive viral culture that is not routinely performed. We hypothesised that RNA viral load (VL) decline time (e-folding time) in people might serve as an alternative marker of infectiousness.
Aim
This study’s objective was to evaluate the association of RNA VL decline time with RNA and PFU VL area under the curve (AUC) and transmission risk for SARS-CoV-2 and influenza A virus.
Methods
In SARS-CoV-2 and influenza A virus community cohorts, viral RNA was quantified by reverse transcription quantitative PCR in serial upper respiratory tract (URT)-samples collected within households after an initial household-member tested positive for one virus. We evaluated correlations between RNA VL decline time and RNA and PFU-VL AUC. Associations between VL decline time and transmission risk in index-contact pairs were assessed.
Results
In SARS-CoV-2 cases, we observed positive correlations between RNA VL decline time and RNA and PFU VL AUC with posterior probabilities 1 and 0.96 respectively. In influenza A cases a positive correlation between RNA VL decline time and RNA VL AUC was observed, with posterior probability of 0.87. Index case VL decline times one standard deviation above the cohort-mean showed a relative increase in secondary attack rates of 39% (95% credible interval (CrI): −6.9 to 95%) for SARS-CoV-2 and 25% (95% CrI: −11 to 71%) for influenza A virus.
Conclusion
We identify VL decline time as a potential marker of infectiousness and transmission risk for SARS-CoV-2 and influenza A virus. Early ascertainment of VL kinetics as part of surveillance of new viruses or variants could inform public health decision making.
Infectiousness of respiratory viral infections is quantified as plaque forming units (PFU), requiring resource-intensive viral culture that is not routinely performed. We hypothesised that RNA viral load (VL) decline time (e-folding time) in people might serve as an alternative marker of infectiousness.
Aim
This study’s objective was to evaluate the association of RNA VL decline time with RNA and PFU VL area under the curve (AUC) and transmission risk for SARS-CoV-2 and influenza A virus.
Methods
In SARS-CoV-2 and influenza A virus community cohorts, viral RNA was quantified by reverse transcription quantitative PCR in serial upper respiratory tract (URT)-samples collected within households after an initial household-member tested positive for one virus. We evaluated correlations between RNA VL decline time and RNA and PFU-VL AUC. Associations between VL decline time and transmission risk in index-contact pairs were assessed.
Results
In SARS-CoV-2 cases, we observed positive correlations between RNA VL decline time and RNA and PFU VL AUC with posterior probabilities 1 and 0.96 respectively. In influenza A cases a positive correlation between RNA VL decline time and RNA VL AUC was observed, with posterior probability of 0.87. Index case VL decline times one standard deviation above the cohort-mean showed a relative increase in secondary attack rates of 39% (95% credible interval (CrI): −6.9 to 95%) for SARS-CoV-2 and 25% (95% CrI: −11 to 71%) for influenza A virus.
Conclusion
We identify VL decline time as a potential marker of infectiousness and transmission risk for SARS-CoV-2 and influenza A virus. Early ascertainment of VL kinetics as part of surveillance of new viruses or variants could inform public health decision making.
Date Issued
2025-02-13
Date Acceptance
2024-08-21
Citation
Eurosurveillance, 2025, 30 (6)
ISSN
1560-7917
Publisher
European Centre for Disease Control and Prevention (ECDC)
Start Page
2
Journal / Book Title
Eurosurveillance
Volume
30
Issue
6
Copyright Statement
© Creative Commons License This work is licensed under a Creative Commons Attribution 4.0 International License.
License URL
Identifier
https://www.ncbi.nlm.nih.gov/pubmed/39949319
Subjects
SARS-CoV-2
clearance time
decline rate
decline time
infectiousness
influenza A
transmission risk
viral load kinetics
Humans
Viral Load
SARS-CoV-2
Influenza, Human
Hong Kong
COVID-19
Influenza A virus
RNA, Viral
Respiratory Tract Infections
Adult
England
Male
Middle Aged
Female
Adolescent
Kinetics
Child
Publication Status
Published
Coverage Spatial
Sweden
Date Publish Online
2025-02-13