The management of COVID-19 epidemic: estimate of the actual infected population, impact of social distancing and directions for an efficient testing strategy. The case of Italy

This work focuses on the so called ‘first wave' of COVID-19 epidemic (21 February–10 April 2020) and aims at outlining a viable strategy to contain the COVID-19 spread and efficiently plan an exit from lockdown measures. It offers a model to estimate the total number of actual infected among the population at national and regional level inferring from the lethality rate, to fill the proven gap with the number of officially reported cases. The result is the reference population used to develop a forecasting exercise of new daily cases, compared to the reported ones. The eventual discrepancy is analysed in terms of compliance with the restrictive measures or to an insufficient number of tests performed. This simulation indicates that an efficient testing policy is the main actionable measure. Furthermore, the paper estimates the optimal number of tests to be performed at national and regional level, in order to be able to release an increasing number of individuals from restrictive measures. Copyright © 2022 Inderscience Enterprises Ltd.

The management of COVID-19 epidemic: estimate of the actual infected population, impact of social distancing and directions for an efficient testing strategy. The case of Italy

This work focuses on the so called 'first wave' of COVID-19 epidemic (21 February-10 April 2020) and aims at outlining a viable strategy to contain the COVID-19 spread and efficiently plan an exit from lockdown measures. It offers a model to estimate the total number of actual infected among the population at national and regional level inferring from the lethality rate, to fill the proven gap with the number of officially reported cases. The result is the reference population used to develop a forecasting exercise of new daily cases, compared to the reported ones. The eventual discrepancy is analysed in terms of compliance with the restrictive measures or to an insufficient number of tests performed. This simulation indicates that an efficient testing policy is the main actionable measure. Furthermore, the paper estimates the optimal number of tests to be performed at national and regional level, in order to be able to release an increasing number of individuals from restrictive measures.

SARS-CoV-2 RNA Testing Using Different Assays-Impact on Testing Strategies in a Clinical Setting.

In order to assess SARS-CoV-2 real time quantitative polymerase chain reaction (RT-qPCR) results in a real-life setting, three independent laboratories in Graz (Austria) set up a continuous cross comparison schedule. The following test systems were used: The QIAGEN NeuMoDx SARS-CoV-2 Assay, the Allplex™ 2019-nCoV Assay (Seegene) on a MicroLab Nimbus (Hamilton) platform combined with RealStar SARS-CoV-2 RT-PCR Assay (Altona Diagnostics GmbH), and the cobas SARS-CoV-2 test on a fully automated cobas 6800 system (Roche). A total of 200 samples were analysed, 184 (92%) were found to be concordant with all testing platforms, 14 (7%) discordant. Two (1%) samples tested invalid on a single platform and were excluded from further analysis. Discordant results were distributed randomly across the assays. The Ct values from all assays correlated closely with each other. All discordant samples showed Ct values ≥ 26. SARS-CoV-2 RT-qPCR assays may show considerable variability, especially in samples with low viral RNA concentrations. Decision makers should thus balance the advantages and disadvantages of RT-qPCR for mass screening and adopt suitable strategies that ensure a rational management of positive samples with high Ct values.

Model-Based Analysis of SARS-CoV-2 Infections, Hospitalization and Outcome in Germany, the Federal States and Districts.

The coronavirus disease 2019 (COVID-19) pandemic challenged many national health care systems, with hospitals reaching capacity limits of intensive care units (ICU). Thus, the estimation of acute local burden of ICUs is critical for appropriate management of health care resources. In this work, we applied non-linear mixed effects modeling to develop an epidemiological SARS-CoV-2 infection model for Germany, with its 16 federal states and 400 districts, that describes infections as well as COVID-19 inpatients, ICU patients with and without mechanical ventilation, recoveries, and fatalities during the first two waves of the pandemic until April 2021. Based on model analyses, covariates influencing the relation between infections and outcomes were explored. Non-pharmaceutical interventions imposed by governments were found to have a major impact on the spreading of SARS-CoV-2. Patient age and sex, the spread of variant B.1.1.7, and the testing strategy (number of tests performed weekly, rate of positive tests) affected the severity and outcome of recorded cases and could reduce the observed unexplained variability between the states. Modeling could reasonably link the discrepancies between fine-grained model simulations of the 400 German districts and the reported number of available ICU beds to coarse-grained COVID-19 patient distribution patterns within German regions.

Provision of safe patient care during the COVID-19 pandemic despite shared patient rooms in a tertiary hospital.

BACKGROUND: The COVID-19 pandemic has resulted in the disruption of healthcare systems. Vienna General Hospital (VGH), a tertiary hospital located in Austria, ran at almost full capacity despite high levels of community SARS-CoV-2 transmission and limited isolation room capacity. To ensure safe patient care, a bundle of infection prevention and control (IPC) measures including universal pre-admission screening and serial SARS-CoV-2 testing during hospitalization was implemented. We evaluated whether testing as part of our IPC approach was effective in preventing hospital outbreaks during different stages of the pandemic. METHODS: In this retrospective single center study, we analyzed the SARS-CoV-2 PCR test results of cases admitted to VGH between a low (15/05/2020-01/08/2020) and a high incidence period (15/09/2020-18/05/2021). Outcomes were the diagnostic yield of (a) admission screening, (b) the yield of serial testing during hospitalization and (c) the occurrence of healthcare-associated COVID-19 (HA-COVID-19) and SARS-CoV-2 related hospital outbreaks. RESULTS: The admission test positivity rate was 0.2% during the low and 2.3% during the high incidence phase. Regarding test conversions, 0.04% (low incidence phase) and 0.5% (high incidence phase) of initially negative cases converted to a positive test result within 7 days after admission The HA-COVID-19 incidence rate per 100,000 patient days was 1.0 (low incidence phase) and 10.7 (high incidence phase). One COVID-19 outbreak affecting eight patients in total could be potentially ascribed to the non-compliance with our IPC protocol. CONCLUSION: Testing in conjunction with other IPC measures enabled the safe provision of patient care at a hospital with predominantly shared patient rooms despite high case numbers in the community.

Free PoC Testing for SARS-CoV-2 in Germany: Factors Expanding Access to Various Communities in a Medium-Sized City.

During the third wave of the COVID-19 (coronavirus disease 2019) pandemic in Germany, free SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) point-of-care (PoC) antigen tests were offered to citizens at least once a week to prevent spreading by asymptomatic infected individuals. This study investigated user groups, timing, frequency, and test center locations in a typical medium-sized European city. We analyzed 27,369 pseudonymized datasets from eight centers over 12 weeks. Those were evaluated according to age, residence, appointment, and potential repeated test occurrence. The centers were visited by different groups; some centers were preferred by a predominantly younger demographic, whereas a mobile option attracted an older age group by reaching districts with few other testing possibilities. Elderly individuals were tested more spontaneously than younger individuals, and a test center at a 'park and ride' had more spontaneous visitors from outside of the city compared to other test locations. Only a small proportion of less than 4% came for testing more than five times. To preferably address many people for voluntary antigen testing, it is crucial to offer different test opportunities accounting for individual behavioral patterns, despite this requiring more complex and costly design than conventional forms.

COVID-19 case findings and contact tracing in South German nursing homes.

BACKGROUND: The air borne SARS-CoV-2 poses a high threat to the elderly and people with underlying diseases. COVID-19 spread quickly in South German nursing homes and for this reason called for preventive measures by the German government. The aim of this paper is to showcase the testing strategies implemented by the Public Health Department Reutlingen to control the spread of COVID-19 in local nursing homes and to report the results thereof. METHODS: This study reports COVID-19 outbreaks in nursing homes in Reutlingen County and how they were dealt with through extensive testing, contact tracing, isolation and hygiene inspections. The testing strategy consisted of three phases: In phase 1 only suspected cases, in phase 2 all staff and residents, and in phase 3 all suspected cases and their contacts were tested. RESULTS: Nearly all residents (98%) and staff members (92%) of all nursing homes in Reutlingen County were tested for SARS-COV-2. 25 of 37 nursing homes had COVID-19 cases, 5 had 30-81 cases/home. 62% of the 395 nursing homes cases were residents, but less than half of them exhibited symptoms (41%). The cases uncovered in nursing homes represented 26% of all 1529 cases in Reutlingen County during the time of this study. CONCLUSIONS: Many COVID-19 cases were discovered through extensive testing, allowing for early interventions. The results shed light on the COVID-19 situation in nursing homes and allowed for individually designed preventive measures. The results also lead to a change in the German legislation. The outbreak management methods of the Public Health Department Reutlingen may also be applicable in other countries.

Real World Performance of SARS-CoV-2 Antigen Rapid Diagnostic Tests in Various Clinical Settings.

OBJECTIVE: To assess the validity of Antigen rapid diagnostic tests (Ag-RDT) for SARS-CoV-2 as decision support tool in various hospital-based clinical settings. DESIGN: Retrospective cohort study among symptomatic and asymptomatic patients and Healthcare workers (HCW). SETTING: A large tertiary teaching medical center serving as a major COVID-19 hospitalizing facility. PARTICIPANTS AND METHODS: Ag-RDTs' performance was assessed in three clinical settings: 1. Symptomatic patients and HCW presenting at the Emergency Departments 2. Asymptomatic patients screened upon hospitalization 3. HCW of all sectors tested at the HCW clinic following exposure. RESULTS: We obtained 5172 samples from 4595 individuals, who had both Ag-RDT and quantitative real-time PCR (qRT-PCR) results available. Of these, 485 samples were positive by qRT-PCR. The positive percent agreement (PPA) of Ag-RDT was greater for lower cycle threshold (Ct) values, reaching 93% in cases where Ct-value was <25 and 85% where Ct-value was <30. PPA was similar between symptomatic and asymptomatic individuals. We observed a significant correlation between Ct-value and time from infection onset (p<0.001). CONCLUSIONS: Ag-RDT are highly sensitive to the infectious stage of COVID-19 manifested by either high viral load (lower Ct) or proximity to infection, whether patient is symptomatic or asymptomatic. Thus, this simple-to-use and inexpensive detection method can be used as a decision support tool in various in-hospital clinical settings, assisting patient flow and maintaining sufficient hospital staffing.

Mutual relationships between SARS-CoV-2 test numbers, fatality and morbidity rates.

BACKGROUND: The number of SARS-CoV-2 tests conversely to other factors, such as age of population or comorbidities, influencing SARS-CoV-2 morbidity and fatality rates, can be increased or decreased by decision makers depending on the development of the pandemic, operational capacity, and financial restraints. The key objective of this study is to identify and describe, within the probabilistic approach, the relationships between SARS-CoV-2 test numbers and the mortality and morbidity rates. METHODS: The study is based on a statistical analysis of 1058 monthly observations relating to 107 countries, from six different continents, in an 11-month period from March 2020 to January 2021. The variable utilised can be defined as the number of tests performed in a given country in 1 month, to the number of cases reported in a prior month and morbidities and mortalities per 1 million population. The probabilities of different mortality and morbidity rates for different test numbers were determined by moving percentiles and fitted by the power law and by the three-segment piecewise-linear approximation based on Theil Sen trend lines. RESULTS: We have identified that for a given probability the dependence of mortality and morbidity rates on SARS-CoV-2 test rates follows a power law and it is well approximated by the three Theil Sen trend lines in the three test rate ranges. In all these ranges Spearman rho and Kendall tau-b rank correlation coefficients of test numbers and morbidity with fatality rates have values between - 0.5 and - 0.12 with p-values below 0.002. CONCLUSIONS: According to the ABC classification: the most important, moderately important, and relatively unimportant ranges of test numbers for managing and control have been indicated based on the value of the Theil Sen trend line slope in the three SARS-CoV-2 test rate ranges identified. Recommendations for SARS-CoV-2 testing strategy are provided.

Evaluation of the Elecsys SARS-CoV-2 antigen assay for the detection of SARS-CoV-2 in nasopharyngeal swabs.

AIMS: The aim of this study was to evaluate the performance of the automated Elecsys® SARS-CoV-2 antigen assay compared to RT-PCR taken as the gold standard for SARS-CoV-2 detection. METHODS: 225 nasopharyngeal swabs were randomly collected among which 123 were tested positive and 102 negatives for SARS-CoV-2 based on RT-PCR. Antigen dosing were performed on a Cobas 8000 e801 analyzer. RESULTS: The antigen test diagnosed SARS-CoV-2 infection status with an overall sensitivity of 65,85% (95% CI 56,76-74,16%), a specificity of 100% (95% CI 96,49-100%) with a Cut-off value ≥ 1. When the cut-off value for the antigen assay was set to > 0,673 COI, the accuracy reached its highest level with a sensitivity of 74,8% (95% CI 66,2 - 82,2%) and a specificity of 97,1% (95% CI 91,6 - 99,4%). Imprecision was estimated in accordance with manufacturer's claims. CONCLUSIONS: We obtained an overall sensitivity of 65,85% (95% CI 56,76-74,16%) and a specificity of 100% (95% CI 96,49-100%), slightly higher than the results reported by the manufacturer. Yet, it remains relatively low comparatively to what is generally acceptable for these antigenic assays (a relative sensitivity of 80%). We also noticed that the accuracy could reach its highest level if the cut-off is set above 0,673 which is lower than established by the manufacturer. Thus, our results suggest that the Elecsys® SARS-CoV-2 Antigen assays, should be improved prior to be used in a SARS-Cov-2 screening strategy. However, if one antigenic assay could demonstrate acceptable performance, it might be centralized in clinical laboratories, keeping the RT-PCR in a second phase for confirmation.

Detection of a COVID-19 cluster by universal SARS-CoV-2 testing in a geriatric hospital and implications for infection control management.

Hospital-level COVID-19 testing strategies may require rapid changes depending on the dynamics of local epidemiology. A COVID-19 outbreak in a hospital near the authors' institution, a Geriatric Medicine centre in Berlin, Germany, prompted the implementation of comprehensive SARS-CoV-2 testing. Serial nasopharyngeal swabs were collected from all patients and staff and analysed for SARS-CoV-2 virus RNA using quantitative real-time PCR. In total, 11 of 84 patients (13.1%) and 1 of 147 employees (0.68%) tested positive. Of the 11 positive patients, 9 (81.8%) were asymptomatic at the time of testing. The data were used as the basis for adjusting local COVID-19 containment measures. Only one staff-to-staff transmission was observed, and there was no patient-to-patient, patient-to-staff or staff-to-patient transmission. Three patients infected with SARS-CoV2 died, two deaths being attributable to advanced malignant disease and one to COVID-19-associated myocarditis. In conclusion, universal SARS-CoV-2 testing revealed a cluster of predominantly asymptomatic infections, enabled appropriate local COVID-19 containment decisions and presumably contributed to the prevention of in-hospital SARS-CoV-2 transmission.

SARS-CoV-2 screening in cancer outpatients during the second wave of the COVID-19 pandemic : Conclusions for crisis response at a high-volume oncology center.

BACKGROUND: During the second wave of the coronavirus disease 2019 (COVID-19) pandemic Austria suffered one of the highest severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) rates worldwide. We report performance parameters of a SARS-CoV­2 screening program established for cancer outpatients at our center. METHODS: Institutional policy recommended routine biweekly SARS-CoV­2 testing. Adherence to the testing recommendation during the second wave of the COVID-19 pandemic between 1 October and 30 November 2020 was analyzed. The SARS-CoV­2 infection rate during first wave period (21 March to 4 May 2020) was compared to the one during second wave. RESULTS: A total of 1577 cancer patients were seen at our outpatient clinic during the second wave. In 1079/1577 (68.4%) patients, at least 1 SARS-CoV2 test was performed. Overall 2833 tests were performed, 23/1577 (1.5%, 95% confidence interval, CI 1.0-2.2%) patients were tested positive for SARS-CoV­2, which indicates a significant increase compared to the first wave (4/1016; 0.4%, 95% CI 0.1-1.0%) with an odds ratio of 3.9 (95% CI 1.5-10.1; p < 0.005). Patients undergoing active anticancer treatment (172/960; 17.9% not tested) were more likely to have undergone a SARS-CoV­2 test than patients in follow-up or best supportive care (326/617; 52.8% not tested p < 0.001). Furthermore, patients with only 1 visit within 4 weeks were more likely to not have undergone a SARS-CoV­2 test (386/598; 64.5%) compared to patients with 2 or more visits (112/979; 11.4%; p < 0.001). The projected number of patients with undetected SARS-CoV­2 infection during the study period was 5. CONCLUSION: We identified clinical patient parameters influencing SARS-CoV­2 testing coverage in cancer outpatients. Our data can provide information on generation of standard operating procedures and resource allocation during subsequent infection waves.

Web-based, rapid and contactless management of ambulatory patients for SARS-CoV-2-testing.

BACKGROUND: During the SARS-CoV-2 pandemic a mass casualty incident of ambulatory patients occurred at the COVID-19 rapid response infrastructure (CRRI) facility at the University Hospital of Cologne (UHC). We report the development of a patient-centred mobile-device solution to support efficient management of the facility, triage of patients and rapid delivery of test results. METHODS: The UHC-Corona Web Tool (CWT) was developed as a web-based software useable on each patient's smartphone. It provides, among others, a self-reported medical history including type and duration of symptoms and potential risk contacts and links all retrieved information to the digital patient chart via a QR code. It provides scheduling of outpatient appointments and automated transmission of SARS-CoV-2 test results. RESULTS: The UHC-CWT was launched on 9 April 2020. It was used by 28,652 patients until 31 August 2020. Of those, 15,245 (53,2%) consulted the CRRI, representing 43,1% of all CRRI patients during the observed period. There were 8304 (29,0%) specifications concerning travel history and 17,145 (59,8%) indications of ≥1 symptom of SARS-CoV-2 infection. The most frequently indicated symptoms were sore throat (60,0%), headache (50,7%), common cold (45,1%) and cough (42,6%) while 11,057 (40,2%) patients did not report any symptoms. After implementation of the UHC-CWT, the amount of patient contacts per physician rose from 38 to 98,7 per day. The personnel for communication of test results were reduced from four on seven days to one on five days. CONCLUSION: The UHC-CWT is an effective digital solution for management of large numbers of outpatients for SARS-CoV-2 testing.

A Review of COVID-19 Mass Testing in the United Arab Emirates.

Appropriate diagnostic testing to identify persons infected with SARS-COV-2 is a vital part of a health system's ability to control the global pandemic of COVID-19 disease. The primary purpose of this review is to provide an overview of the mass testing strategy implemented throughout the UAE and the overall impact it has made on containing and controlling the spread of the disease. This study describes the mass testing strategy and capacity of the UAE during the pandemic of the new coronavirus SARS-COV-2. The UAE has conducted 15 million polymerase chain reaction (PCR) tests to SARS-COV-2, as of 15 November 2020. The number of tests per day varied from 10,000 by the end of March to 120,000 tests per day in November 2020. The mass testing initiative across the entire UAE forms an integral part of a bigger strategy focusing on testing, tracing contacts and isolating positive cases.

Impact of COVID-19 Testing Strategies and Lockdowns on Disease Management Across Europe, South America, and the United States: Analysis Using Skew-Normal Distributions.

BACKGROUND: As COVID-19 infections worldwide exceed 6 million confirmed cases, the data reveal that the first wave of the outbreak is coming to an end in many European countries. There is variation in the testing strategies (eg, massive testing vs testing only those displaying symptoms) and the strictness of lockdowns imposed by countries around the world. For example, Brazil's mitigation measures lie between the strict lockdowns imposed by many European countries and the more liberal approach taken by Sweden. This can influence COVID-19 metrics (eg, total deaths, confirmed cases) in unexpected ways. OBJECTIVE: This study aimed to evaluate the effectiveness of local authorities' strategies in managing the COVID-19 pandemic in Europe, South America, and the United States. METHODS: The early stage of the COVID-19 outbreak in Brazil was compared to Europe using the weekly transmission rate. Using the European data as a basis for our analysis, we examined the spread of COVID-19 and modeled curves pertaining to daily confirmed cases and deaths per million using skew-normal probability density functions. For Sweden, the United Kingdom, and the United States, we forecasted the end of the pandemic, and for Brazil, we predicted the peak value for daily deaths per million. We also discussed additional factors that could play an important role in the fight against COVID-19, such as the fast response of local authorities, testing strategies, number of beds in the intensive care unit, and isolation strategies adopted. RESULTS: The European data analysis demonstrated that the transmission rate of COVID-19 increased similarly for all countries in the initial stage of the pandemic but changed as the total confirmed cases per million in each country grew. This was caused by the variation in timely action by local authorities in adopting isolation measures and/or massive testing strategies. The behavior of daily confirmed cases for the United States and Brazil during the early stage of the outbreak was similar to that of Italy and Sweden, respectively. For daily deaths per million, transmission in the United States was similar to that of Switzerland, whereas for Brazil, it was greater than the counts for Portugal, Germany, and Austria (which had, in terms of total deaths per million, the best results in Europe) but lower than other European countries. CONCLUSIONS: The fitting skew parameters used to model the curves for daily confirmed cases per million and daily deaths per million allow for a more realistic prediction of the end of the pandemic and permit us to compare the mitigation measures adopted by local authorities by analyzing their respective skew-normal parameters. The massive testing strategy adopted in the early stage of the pandemic by German authorities made a positive difference compared to other countries like Italy where an effective testing strategy was adopted too late. This explains why, despite a strictly indiscriminate lockdown, Italy's mortality rate was one of the highest in the world.

Performance and feasibility of universal PCR admission screening for SARS-CoV-2 in a German tertiary care hospital.

Anamnestic screening of symptoms and contact history is applied to identify coronavirus disease 2019 (COVID-19) patients on admission. However, asymptomatic and presymptomatic patients remain undetected although the viral load may be high. In this retrospective cohort study, all hospitalized patients who received polymerase chain reaction (PCR) admission testing from March 26th until May 24th, 2020 were included. Data on COVID-19-specific symptoms and contact history to COVID-19 cases were retrospectively extracted from patient files and from contact tracing notes. The compliance to the universal testing protocol was high with 90%. Out of 6940 tested patients, 27 new severe acute respiratory syndrome coronavirus-2 infections (0.4%) were detected. Seven of those COVID-19 cases (26% of all new cases) were asymptomatic and had no positive contact history, but were identified through a positive PCR test. The number needed to identify an asymptomatic patient was 425 in the first wave of the epidemic, 1218 in the low incidence phase. The specificity of the method was above 99.9%. Universal PCR testing was highly accepted by staff as demonstrated by high compliance. The costs to detect one asymptomatic case in future studies need to be traded off against the costs and damage caused by potential outbreaks of COVID-19.

Routine testing of close contacts of confirmed COVID-19 cases - National COVID-19 Contact Management Programme, Ireland, May to August 2020.

OBJECTIVES: The objective of this study was to inform public health practitioners who are designing, adapting and implementing testing and tracing strategies for Coronavirus disease (COVID-19) control. STUDY DESIGN: The study design is monitoring and evaluation of a national public health protection programme. METHODS: All close contacts of laboratory-confirmed cases of COVID-19 identified between the 19th May and 2nd August were included; secondary attack rates and numbers needed to test were estimated. RESULTS: Four thousand five hundred eighty six of 7272 (63%) close contacts of cases were tested with at least one test. The secondary attack rate in close contacts who were tested was 7% (95% Confidence Interval [CI]: 6.3 - 7.8%). At the 'day 0' test, 14.6% (95% CI: 11.6-17.6%) of symptomatic close contacts tested positive compared with 5.2% (95% CI: 4.4-5.9%) of asymptomatic close contacts. CONCLUSIONS: The application of additional symptom-based criteria for testing in this high-incidence population (close contacts) is of limited utility because of the low negative predictive value of absence of symptoms.

Validation of a commercially available SARS-CoV-2 serological immunoassay.

OBJECTIVES: To validate the diagnostic accuracy of a Euroimmun SARS-CoV-2 IgG and IgA immunoassay for COVID-19. METHODS: In this unmatched (1:2) case-control validation study, we used sera of 181 laboratory-confirmed SARS-CoV-2 cases and 326 controls collected before SARS-CoV-2 emergence. Diagnostic accuracy of the immunoassay was assessed against a whole spike protein-based recombinant immunofluorescence assay (rIFA) by receiver operating characteristic (ROC) analyses. Discrepant cases between ELISA and rIFA were further tested by pseudo-neutralization assay. RESULTS: COVID-19 patients were more likely to be male and older than controls, and 50.3% were hospitalized. ROC curve analyses indicated that IgG and IgA had high diagnostic accuracies with AUCs of 0.990 (95% Confidence Interval [95%CI]: 0.983-0.996) and 0.978 (95%CI: 0.967-0.989), respectively. IgG assays outperformed IgA assays (p=0.01). Taking an assessed 15% inter-assay imprecision into account, an optimized IgG ratio cut-off > 2.5 displayed a 100% specificity (95%CI: 99-100) and a 100% positive predictive value (95%CI: 96-100). A 0.8 cut-off displayed a 94% sensitivity (95%CI: 88-97) and a 97% negative predictive value (95%CI: 95-99). Substituting the upper threshold for the manufacturer's, improved assay performance, leaving 8.9% of IgG ratios indeterminate between 0.8-2.5. CONCLUSIONS: The Euroimmun assay displays a nearly optimal diagnostic accuracy using IgG against SARS-CoV-2 in patient samples, with no obvious gains from IgA serology. The optimized cut-offs are fit for rule-in and rule-out purposes, allowing determination of whether individuals in our study population have been exposed to SARS-CoV-2 or not. IgG serology should however not be considered as a surrogate of protection at this stage.