TY - JOUR
AU - Walker, Sarah A
AU - Pritchard, Emma
AU - House, Thomas
AU - Robotham, Julie V
AU - Birrell, Paul J.
AU - Bell, Iain
AU - Bell, John I.
AU - Newton, John N.
AU - Farrar, Jeremy
AU - Diamond, Ian
AU - Studley, Ruth
AU - Hay, Jodie
AU - Vihta, Karina-Doris
AU - Peto, Timothy E.A.
AU - Stoesser, Nicole
AU - Matthews, Philippa C.
AU - Eyre, David W.
AU - Pouwels, Koen B.
PY - 2021
DA - July
TI - Ct threshold values, a proxy for viral load in community SARS-CoV-2 cases, demonstrate wide variation across populations and over time
JO - ELife
VL - 10
DO - http://dx.doi.org/10.7554/elife.64683
AB - Background: Information on SARS-CoV-2 in representative community surveillance is limited, particularly cycle threshold (Ct) values (a proxy for viral load). Methods: We included all positive nose and throat swabs 26 April 2020 to 13 March 2021 from the UK’s national COVID-19 Infection Survey, tested by RT-PCR for the N, S, and ORF1ab genes. We investigated predictors of median Ct value using quantile regression. Results: Of 3,312,159 nose and throat swabs, 27,902 (0.83%) were RT-PCR-positive, 10,317 (37%), 11,012 (40%), and 6550 (23%) for 3, 2, or 1 of the N, S, and ORF1ab genes, respectively, with median Ct = 29.2 (~215 copies/ml; IQR Ct = 21.9–32.8, 14–56,400 copies/ml). Independent predictors of lower Cts (i.e. higher viral load) included self-reported symptoms and more genes detected, with at most small effects of sex, ethnicity, and age. Single-gene positives almost invariably had Ct &gt; 30, but Cts varied widely in triple-gene positives, including without symptoms. Population-level Cts changed over time, with declining Ct preceding increasing SARS-CoV-2 positivity. Of 6189 participants with IgG S-antibody tests post-first RT-PCR-positive, 4808 (78%) were ever antibody-positive; Cts were significantly higher in those remaining antibody negative. Conclusions: Marked variation in community SARS-CoV-2 Ct values suggests that they could be a useful epidemiological early-warning indicator. Funding: Department of Health and Social Care, National Institutes of Health Research, Huo Family Foundation, Medical Research Council UK; Wellcome Trust.
PB - eLife Sciences Publications
UR - http://eprints.gla.ac.uk/248019/
KW - Coronavirus (COVID-19)
ER