key: cord-0715494-oe4bzale
authors: Aitman, T. J.; Bauld, L.; Carruthers, K. F.; Gilbert, N.; Turok, N.
title: COVID-19 testing: disparity between national and institution-based case detection
date: 2022-03-01
journal: nan
DOI: 10.1101/2022.02.21.22270847
sha: a918928d10f5718024df7b377cb70d029d314573
doc_id: 715494
cord_uid: oe4bzale

Reports of COVID-19 prevalence through national statistics, community surveys and targeted testing at places of work or study have guided national and institutional responses to the pandemic. The University of Edinburgh established a mass testing programme, TestEd, for detection of COVID-19 in asymptomatic staff and students who are studying or working on campus. The study has tested more than 100,000 samples with more than 170 confirmed positive results. Since the introduction of a change in policy in England and the UK devolved nations in early January 2022, to limit eligibility for PCR testing in the community to those with symptoms, we have noticed a divergence between the reports in Scottish and UK-wide prevalence, and the magnitude and frequency of positive results in the University datasets. While the national UK-wide and Scottish case figures show declining or stable prevalence, University case reports have risen more than five-fold since early December 2021 and continue to rise. These observations could be important in the face of future variants of concern and emphasise the need for continued access to high sensitivity PCR testing and other forms of surveillance.

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Reports of COVID-19 prevalence through national statistics, community surveys and targeted testing at places of work or study have guided national and institutional responses to the pandemic. However, strategies for infection control targeted solely at individuals with symptoms are unlikely to be completely effective at containing viral spread, because around 50% of transmission has been observed to occur from pre-or asymptomatic individuals. 1 The University of Edinburgh established a mass testing programme, TestEd, 2 for detection of COVID-19 in asymptomatic staff and students who are studying or working on campus.

Because TestEd participants don't have symptoms, individuals in this population who are pre-or asymptomatic carriers would not realise the risk they pose in transmitting the virus to colleagues or peers in the absence of a positive test. In this report, we compared the frequency of positive test results from the TestEd programme, from March 2021 -February 2022, with the reports of positive cases from the University of Edinburgh reporting system and published national data from Public Health Scotland.

Data was collected from three different sources.

(i) The University of Edinburgh mass testing programme, TestEd, uses pooled saliva-based testing by PCR, with a protocol adapted from our previously published approach for nasopharyngeal swab testing. 3 The study has tested more than 100,000 samples with more than 170 confirmed positive results. Specificity is > 99% and sensitivity, based on controlled samples, is 93-97%. Results are reported daily but collated and presented weekly.

(ii) UoE cases: The University collates data from across the University according to University guidelines requiring anyone testing positive via any route (LFD, NHS test, Tested) to report this on a standard online form to the University. This data was collated on a weekly basis and tests from all routes were combined to give a weekly report of positive cases within the University. A small proportion of positive cases reported to the University came from TestEd. However, because the TestEd protocol aimed routinely to test only asymptomatic participants and the majority of cases reported to the University were largely symptomatic, the overlap is small (less than 5% of overall University cases) and positive cases that were present in both datasets were not removed. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted March 1, 2022. ; https://doi.org/10.1101/2022.02.21.22270847 doi: medRxiv preprint (iii) Daily reports of positive cases were downloaded from the COVID-19 Daily Dashboard on the Public Health Scotland web site and collated to give a weekly case report.

Since the introduction of a change in policy in England and the UK devolved nations to limit eligibility for PCR testing in the community to those with symptoms, we noticed a divergence between the reports in Scottish and UK-wide prevalence, and the magnitude and frequency of positive results in the University datasets. This change in eligibility for PCR tests took effect in Scotland from 6 th January 2022, following which national data reporting was adjusted from 13 th January 2022 to reflect this revision. 4 Cases are now a combination of self-reported lateral flow tests (intended for asymptomatic individuals in the community) and those with symptoms who are still encouraged to seek a PCR test.

The national UK-wide and Scottish case figures show declining or stable prevalence. In contrast, University case reports have risen more than five-fold since early December 2021 and continue to rise (Figure) . A similar rise was observed in both University staff and students. The TestEd result, from a relatively stable sample of regular, asymptomatic participants, may be less prone to reporting biases than the present national statistics.

Our PCR and sequencing data and analysis of the demographics of the individuals testing positive suggest that the rise in prevalence in the University population is reflective of a substantial increase in viral prevalence that is not reflected in nationally reported positive case numbers. This has also been observed in other UK-wide data sources including the ZOE app study. 5 Although there are potential sources of data bias, including increased testing amongst mildly symptomatic cases and local changes in viral strain, we suggest these results are most likely due to reduced testing and, in particular, a dearth of reporting of positive LFT is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted March 1, 2022. ; https://doi.org/10.1101/2022.02.21.22270847 doi: medRxiv preprint

Transmission heterogeneities, kinetics, and controllability of SARS-CoV-2

It is made available under a perpetuity.is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprintThe copyright holder for this this version posted March 1, 2022. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint