Exhaled SARS-CoV-2 RNA viral load kinetics measured by facemask sampling associates with household transmission

Affiliations

¹ Department of Respiratory Sciences, University of Leicester, Leicester, UK; Department of Infectious Diseases and HIV Medicine, University Hospitals of Leicester NHS Trust, Leicester, UK; Li Ka Shing Center for Health Information and Discovery, Oxford Big Data Institute, University of Oxford, UK. Electronic address: Daniel.pan@nhs.net.
² Department of Respiratory Sciences, University of Leicester, Leicester, UK; Department of Clinical Microbiology, University Hospitals of Leicester NHS Trust, Leicester, UK.
³ Department of Respiratory Sciences, University of Leicester, Leicester, UK.
⁴ Department of Cardiovascular Sciences, University Hospitals of Leicester NHS Trust, Leicester, UK.
⁵ Department of Infectious Diseases and HIV Medicine, University Hospitals of Leicester NHS Trust, Leicester, UK.
⁶ Department of Engineering, University of Leicester, Leicester, UK.
⁷ Department of Respiratory Sciences, University of Leicester, Leicester, UK; Department of Infectious Diseases and HIV Medicine, University Hospitals of Leicester NHS Trust, Leicester, UK.

PMID: 35843566
PMCID: PMC9281452
DOI: 10.1016/j.cmi.2022.07.005

Exhaled SARS-CoV-2 RNA viral load kinetics measured by facemask sampling associates with household transmission

Daniel Pan et al. Clin Microbiol Infect. 2023 Feb.

. 2023 Feb;29(2):254.e1-254.e6.

doi: 10.1016/j.cmi.2022.07.005. Epub 2022 Jul 14.

Authors

Affiliations

¹ Department of Respiratory Sciences, University of Leicester, Leicester, UK; Department of Infectious Diseases and HIV Medicine, University Hospitals of Leicester NHS Trust, Leicester, UK; Li Ka Shing Center for Health Information and Discovery, Oxford Big Data Institute, University of Oxford, UK. Electronic address: Daniel.pan@nhs.net.
² Department of Respiratory Sciences, University of Leicester, Leicester, UK; Department of Clinical Microbiology, University Hospitals of Leicester NHS Trust, Leicester, UK.
³ Department of Respiratory Sciences, University of Leicester, Leicester, UK.
⁴ Department of Cardiovascular Sciences, University Hospitals of Leicester NHS Trust, Leicester, UK.
⁵ Department of Infectious Diseases and HIV Medicine, University Hospitals of Leicester NHS Trust, Leicester, UK.
⁶ Department of Engineering, University of Leicester, Leicester, UK.
⁷ Department of Respiratory Sciences, University of Leicester, Leicester, UK; Department of Infectious Diseases and HIV Medicine, University Hospitals of Leicester NHS Trust, Leicester, UK.

PMID: 35843566
PMCID: PMC9281452
DOI: 10.1016/j.cmi.2022.07.005

Abstract

Objectives: No studies have examined longitudinal patterns of naturally exhaled SARS-CoV-2 RNA viral load (VL) during acute infection. We report this using facemask sampling (FMS) and assessed the relationship between emitted RNA VL and household transmission.

Methods: Between December 2020 and February 2021, we recruited participants within 24 hours of a positive RT-qPCR on upper respiratory tract sampling (URTS) (day 0). Participants gave FMS (for 1 hour) and URTS (self-taken) on seven occasions up to day 21. Samples were analysed by RT-qPCR (from sampling matrix strips within the mask) and symptom diaries were recorded. Household transmission was assessed through reporting of positive URTS RT-qPCR in household contacts.

Results: Analysis of 203 FMS and 190 URTS from 34 participants showed that RNA VL peaked within the first 5 days following sampling. Concomitant URTS, FMS RNA VL, and symptom scores, however, were poorly correlated, but a higher severity of reported symptoms was associated with FMS positivity up to day 5. Of 28 participants who had household contacts, 12 (43%) reported transmission. Frequency of household transmission was associated with the highest (peak) FMS RNA VL obtained (negative genome copies/strip: 0% household transmission; 1 to 1000 copies/strip: 20%; 1001 to 10 000 copies/strip: 57%; >10 000 copies/strip: 75%; p = 0.048; age adjusted OR of household transmission per log increase in copies/strip: 4.97; 95% CI, 1.20-20.55; p = 0.02) but not observed with peak URTS RNA VL.

Discussion: Exhaled RNA VL measured by FMS is highest in early infection, can be positive in symptomatic patients with concomitantly negative URTS, and is strongly associated with household transmission.

Keywords: Airborne; COVID-19; Exhaled virus; Facemask sampling; Nasopharyngeal sampling; Respiratory viruses; SARS-CoV-2; Transmission; Viral diagnostics; Viral load.

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Figures

**Fig. 1**
(a) Timeline of participant recruitment into the study. (b) Flowchart of participants through the study.

**Fig. 2**
Proportion of facemask sampling and upper respiratory tract sampling positive samples over 21 days and complete dataset with lines showing daily mean values (biased toward high RNA viral load [VL]). Results from individuals giving negative results throughout were excluded. RNA VL are classified as viral genome copies per strip for FMS or per 100 μL for URTS. The dotted line at 250 genomes indicates the lower limit of quantification. VL, viral load.

**Fig. 3**
a (left): Relationships between peak viral loads and probable household transmission for FMS and URTS. FMS, facemask sampling; TR+, transmission positive; URTS, upper respiratory tract sampling. b (right): Higher and more prolonged FMS positivity associated with household transmission due to infectious participants (red), compared to no household transmission from non-infectious participants (black). E gene copies/strip expressed as geometric means + 95% CIs. Viral load units are classified as viral genome copies per strip for FMS.

See this image and copyright information in PMC

References

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Exhaled SARS-CoV-2 RNA viral load kinetics measured by facemask sampling associates with household transmission

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Exhaled SARS-CoV-2 RNA viral load kinetics measured by facemask sampling associates with household transmission

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