Genomic epidemiology of SARS-CoV-2 in a UK university identifies dynamics of transmission (preprint)

Understanding the drivers for spread of SARS-CoV-2 in higher education settings is important to limit transmission between students, and onward spread into at-risk populations. In this study, we prospectively sequenced 482 SARS-CoV-2 isolates derived from asymptomatic student screening and symptomatic testing of students and staff at the University of Cambridge from 5 October to 6 December 2020. We performed a detailed phylogenetic comparison with 972 isolates from the surrounding community, complemented with epidemiological and contact tracing data, to determine transmission dynamics. After a limited number of viral introductions into the university, the majority of student cases were linked to a single genetic cluster, likely dispersed across the university following social gatherings at a venue outside the university. We identified considerable onward transmission associated with student accommodation and courses; this was effectively contained using local infection control measures and dramatically reduced following a national lockdown. We observed that transmission clusters were largely segregated within the university or within the community. This study highlights key determinants of SARS-CoV-2 transmission and effective interventions in a higher education setting that will inform public health policy during pandemics.

Feasibility and efficacy of mass testing for SARS-CoV-2 in a UK university using swab pooling and PCR (preprint)

Transmission of SARS-CoV-2 without symptoms is well described, and may be mitigated by mass testing. Nonetheless, the optimal implementation and quantitative real-world impact of this approach remain unclear. During a period of rising SARS-CoV-2 prevalence, students at the University of Cambridge were enrolled in a voluntary programme of weekly PCR-based asymptomatic screening. Swab pooling by household reduced the total testing capacity required by five-fold, without affecting laboratory workflows or compromising test sensitivity. Participation remained >75% throughout the study period. 299/671 (45%) of students diagnosed with SARS-CoV-2 were either identified or pre-emptively quarantined because of the screening programme. After a negative screening test, the risk of developing COVID-19 over the following 7 days was decreased by 51%. Modelling transmission using parameters from our study suggests a reduction in R0 of up to 31% attributable to weekly screening. We therefore demonstrate the feasibility and efficacy of regular, voluntary mass testing for COVID-19.

A Prospective Study of Risk Factors Associated with Seroprevalence of SARS-CoV-2 Antibodies in Healthcare Workers at a Large UK Teaching Hospital (preprint)

Background: The COVID-19 pandemic continues to grow at an unprecedented rate. Healthcare workers (HCWs) are at higher risk of SARS-CoV-2 infection than the general population but risk factors for HCW infection are not well described.Methods: We conducted a prospective sero-epidemiological study of HCWs at a UK teaching hospital using a SARS-CoV-2 immunoassay. Risk factors for seropositivity were analysed using multivariate logistic regression.Findings: 410/5,698 (7·2%) staff tested positive for SARS-CoV-2 antibodies. Seroprevalence was higher in those working in designated COVID-19 areas compared with other areas (9·47% versus 6·16%) Healthcare assistants (aOR 2·06 [95%CI 1·14-3·71]; p =0·016) and domestic and portering staff (aOR 3·45 [95% CI 1·07-11·42]; p =0·039) had significantly higher seroprevalence than other staff groups after adjusting for age, sex, ethnicity and COVID-19 working location. Staff working in acute medicine and medical sub-specialities were also at higher risk (aOR 2·07 [95% CI 1·31-3·25]; p <0·002). Staff from Black, Asian and minority ethnic (BAME) backgrounds had an aOR of 1·65 (95% CI 1·32 – 2·07; p <0·001) compared to white staff; this increased risk was independent of COVID-19 area working. The only symptoms significantly associated with seropositivity in a multivariable model were loss of sense of taste or smell, fever and myalgia; 31% of staff testing positive reported no prior symptoms.Interpretation: Risk of SARS-CoV-2 infection amongst HCWs is heterogeneous and influenced by COVID-19 working location, role, age and ethnicity. Increased risk amongst BAME staff cannot be accounted for solely by occupational factors.Funding: Wellcome Trust, Addenbrookes Charitable Trust, National Institute for Health Research, Academy of Medical Sciences, the Health Foundation and the NIHR Cambridge Biomedical Research Centre.Declaration of Interests: None to declare.Ethics Approval Statement: Ethical approval for this study was granted by the East of England – Cambridge Central Research Ethics Committee (IRAS ID: 220277).

A prospective study of risk factors associated with seroprevalence of SARS-CoV-2 antibodies in healthcare workers at a large UK teaching hospital (preprint)

Background The COVID-19 pandemic continues to grow at an unprecedented rate. Healthcare workers (HCWs) are at higher risk of SARS-CoV-2 infection than the general population but risk factors for HCW infection are not well described. Methods We conducted a prospective sero-epidemiological study of HCWs at a UK teaching hospital using a SARS-CoV-2 immunoassay. Risk factors for seropositivity were analysed using multivariate logistic regression. Findings 410/5,698 (7.2%) staff tested positive for SARS-CoV-2 antibodies. Seroprevalence was higher in those working in designated COVID-19 areas compared with other areas (9.47% versus 6.16%) Healthcare assistants (aOR 2.06 [95%CI 1.14-3.71]; p=0.016) and domestic and portering staff (aOR 3.45 [95% CI 1.07-11.42]; p=0.039) had significantly higher seroprevalence than other staff groups after adjusting for age, sex, ethnicity and COVID-19 working location. Staff working in acute medicine and medical sub-specialities were also at higher risk (aOR 2.07 [95% CI 1.31-3.25]; p=0.002). Staff from Black, Asian and minority ethnic (BAME) backgrounds had an aOR of 1.65 (95% CI 1.32-2.07; p<0.0001) compared to white staff; this increased risk was independent of COVID-19 area working. The only symptoms significantly associated with seropositivity in a multivariable model were loss of sense of taste or smell, fever and myalgia; 31% of staff testing positive reported no prior symptoms. Interpretation Risk of SARS-CoV-2 infection amongst HCWs is heterogeneous and influenced by COVID-19 working location, role, age and ethnicity. Increased risk amongst BAME staff cannot be accounted for solely by occupational factors. Funding Wellcome Trust, Addenbrookes Charitable Trust, National Institute for Health Research, Academy of Medical Sciences, the Health Foundation and the NIHR Cambridge Biomedical Research Centre.

A2B-COVID: A method for evaluating potential SARS-CoV-2 transmission events (preprint)

Identifying linked cases of infection is a key part of the public health response to viral infectious disease. Viral genome sequence data is of great value in this task, but requires careful analysis, and may need to be complemented by additional types of data. The Covid-19 pandemic has highlighted the urgent need for analytical methods which bring together sources of data to inform epidemiological investigations. We here describe A2B-COVID, an approach for the rapid identification of linked cases of coronavirus infection. Our method combines knowledge about infection dynamics, data describing the movements of individuals, and novel approaches to genome sequence data to assess whether or not cases of infection are consistent or inconsistent with linkage via transmission. We apply our method to analyse and compare data collected from two wards at Cambridge University Hospitals, showing qualitatively different patterns of linkage between cases on designated Covid-19 and non-Covid-19 wards. Our method is suitable for the rapid analysis of data from clinical or other potential outbreak settings.

COVID-19 infection dynamics in care homes in the East of England: a retrospective genomic epidemiology study (preprint)

Background COVID-19 poses a major challenge to infection control in care homes. SARS-CoV-2 is readily transmitted between people in close contact and causes disproportionately severe disease in older people. Methods Data and SARS-CoV-2 samples were collected from patients in the East of England (EoE) between 26th February and 10th May 2020. Care home residents were identified using address search terms and Care Quality Commission registration information. Samples were sequenced at the University of Cambridge or the Wellcome Sanger Institute and viral clusters defined based on genomic and time differences between cases. Findings 7,406 SARS-CoV-2 positive samples from 6,600 patients were identified, of which 1,167 (18.2%) were residents from 337 care homes. 30/71 (42.3%) care home residents tested at Cambridge University Hospitals NHS Foundation Trust (CUH) died. Genomes were available for 700/1,167 (60%) residents from 292 care homes, and 409 distinct viral clusters were defined. We identified several probable transmissions between care home residents and healthcare workers (HCW). Interpretation Care home residents had a significant burden of COVID-19 infections and high mortality. Larger viral clusters were consistent with within-care home transmission, while multiple clusters per care home suggested independent acquisitions.

Rapid point of care nucleic acid testing for SARS-CoV-2 in hospitalised patients: a clinical trial and implementation study (preprint)

BackgroundThere is urgent need for safe and efficient triage protocols for hospitalized COVID-19 suspects to appropriate isolation wards. A major barrier to timely discharge of patients from the emergency room and hospital is the turnaround time for many SARS-CoV-2 nucleic acid tests. We validated a point of care nucleic acid amplification based platform SAMBA II for diagnosis of COVID-19 and performed an implementation study to assess its impact on patient disposition at a major academic hospital. MethodsWe prospectively recruited COVID-19 suspects admitted to hospital (NCT04326387). In an initial pilot phase, individuals were tested using a nasal/throat swab with the SAMBA II SARS-CoV-2 rapid diagnostic platform in parallel with a combined nasal/throat swab for standard central laboratory RT-PCR testing. In the second implementation phase, we examined the utility of adding the SAMBA platform to routine care. In the pilot phase, we measured concordance and assay validity using the central laboratory as the reference standard and assessed assay turnaround time. In the implementation phase, we assessed 1) time to definitive bed placement from admission, 2) time spent on COVID-19 holding wards, 3) proportion of patients in isolation versus COVID negative areas following a test, comparing the implementation phase with the 10 days prior to implementation. ResultsIn phase I, 149 participants were included in the pilot. By central laboratory RT-PCR testing, 32 (21.5%) tested positive and 117 (78.5%). Sensitivity and specificity of the SAMBA assay compared to RT-PCR lab test were 96.9% (95% CI 0.838-0.999) and 99.1% (0.953-0.999), respectively. Median time to result was 2.6 hours (IQR 2.3 to 4.8) for SAMBA II SARS-CoV-2 test and 26.4 hours (IQR 21.4 to 31.4) for the standard lab RT-PCR test (p<0.001). In the first 10 days of the SAMBA implementation phase, we conducted 992 tests, with the majority (59.8%) used for hospital admission, and the remainder for pre-operative screening (11.3%), discharge planning (10%), in-hospital screening of new symptoms (9.7%). Comparing the pre-implementation (n=599) with the implementation phase, median time to definitive bed placement from admission was reduced from 23.4 hours (8.6-41.9) to 17.1 hours (9.0-28.8), P=0.02 in Cox analysis, adjusted for age, sex, comorbidities and clinical severity at presentation. Mean length of stay on a COVID-19 holding ward decreased from 58.5 hours to 29.9 hours (P<0.001). Use of single occupancy rooms amongst those tested fell from 30.8% before to 21.2% (P=0.03) and 11 hospital bay closures (on average 6 beds each) were avoided after implementation of the POC assay. ConclusionsThe SAMBA II SARS-CoV-2 rapid assay performed well compared to a centralized laboratory RT-PCR platform and demonstrated shorter time to result both in trial and real-world settings. It was also associated with faster time to definitive bed placement from the emergency room, greater availability of isolation rooms, avoidance of hospital bay closures, and greater movement of patients to COVID negative open "green" category wards. Rapid testing in hospitals has the potential to transform ability to deal with the COVID-19 epidemic.

Rapid implementation of real-time SARS-CoV-2 sequencing to investigate healthcare-associated COVID-19 infections (preprint)

Background The burden and impact of healthcare-associated COVID-19 infections is unknown. We aimed to examine the utility of rapid sequencing of SARS-CoV-2 combined with detailed epidemiological analysis to investigate healthcare-associated COVID-19 infections and to inform infection control measures. Methods We set up rapid viral sequencing of SARS-CoV-2 from PCR-positive diagnostic samples using nanopore sequencing, enabling sample-to-sequence in less than 24 hours. We established a rapid review and reporting system with integration of genomic and epidemiological data to investigate suspected cases of healthcare-associated COVID-19. Results Between 13 March and 24 April 2020 we collected clinical data and samples from 5191 COVID-19 patients in the East of England. We sequenced 1000 samples, producing 747 complete viral genomes. We conducted combined epidemiological and genomic analysis of 299 patients at our hospital and identified 26 genomic clusters involving 114 patients. 66 cases (57.9%) had a strong epidemiological link and 15 cases (13.2%) had a plausible epidemiological link. These results were fed back clinical, infection control and hospital management teams, resulting in infection control interventions and informing patient safety reporting. Conclusions We established real-time genomic surveillance of SARS-CoV-2 in a UK hospital and demonstrated the benefit of combined genomic and epidemiological analysis for the investigation of healthcare-associated COVID-19 infections. This approach enabled us to detect cryptic transmission events and identify opportunities to target infection control interventions to reduce further healthcare-associated infections.