Development of indigenous IgG ELISA for the detection of anti-SARS-CoV-2 IgG.

Sapkal G ，Shete-Aich A ，Jain R ，Yadav PD ，Sarkale P ，Lakra R ，Baradkar S ，Deshpande GR ，Mali D ，Tilekar BN ，Majumdar T ，Kaushal H ，Gurav Y ，Gupta N ，Mohandas S ，Deshpande K ，Kaduskar O ，Salve M ，Patil S ，Gaikwad S ，Sugunan AP ，Ashok M ，Giri S ，Shastri J ，Abraham P ，Gangakhedkar RR ，$COVID Support Team: Pawar S., Patshute S., Salve V., Natarajan V., Marwah V., Malhotra B., Jain A., Sathe P., More R., Khedekar R., Suryawanshi D., Kalele K., Kumar A., Upadhyaya C.P., Waghmare A., Gawande P., Gopale S., Acharya M., Holeppanavar M., Thorat S., Chopade G., Vidhate S., Khutwad K., Phagiwala D., Bhanarkar S., Rakhe A., Salvi V., Dhaigude S., Ciyona ... -  《-》

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

To validate the diagnostic accuracy of a Euroimmun SARS-CoV-2 IgG and IgA immunoassay for COVID-19. 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. 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. 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.

Meyer B ，Torriani G ，Yerly S ，Mazza L ，Calame A ，Arm-Vernez I ，Zimmer G ，Agoritsas T ，Stirnemann J ，Spechbach H ，Guessous I ，Stringhini S ，Pugin J ，Roux-Lombard P ，Fontao L ，Siegrist CA ，Eckerle I ，Vuilleumier N ，Kaiser L ，Geneva Center for Emerging Viral Diseases ... -  《-》

Point-of-care serological assays for delayed SARS-CoV-2 case identification among health-care workers in the UK: a prospective multicentre cohort study.

Health-care workers constitute a high-risk population for acquisition of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Capacity for acute diagnosis via PCR testing was limited for individuals with mild to moderate SARS-CoV-2 infection in the early phase of the COVID-19 pandemic and a substantial proportion of health-care workers with suspected infection were not tested. We aimed to investigate the performance of point-of-care and laboratory serology assays and their utility in late case identification, and to estimate SARS-CoV-2 seroprevalence. We did a prospective multicentre cohort study between April 8 and June 12, 2020, in two phases. Symptomatic health-care workers with mild to moderate symptoms were eligible to participate 14 days after onset of COVID-19 symptoms, as per the Public Health England (PHE) case definition. Health-care workers were recruited to the asymptomatic cohort if they had not developed PHE-defined COVID-19 symptoms since Dec 1, 2019. In phase 1, two point-of-care lateral flow serological assays, the Onsite CTK Biotech COVID-19 split IgG/IgM Rapid Test (CTK Bitotech, Poway, CA, USA) and the Encode SARS-CoV-2 split IgM/IgG One Step Rapid Test Device (Zhuhai Encode Medical Engineering, Zhuhai, China), were evaluated for performance against a laboratory immunoassay (EDI Novel Coronavirus COVID-19 IgG ELISA kit [Epitope Diagnostics, San Diego, CA, USA]) in 300 samples from health-care workers and 100 pre-COVID-19 negative control samples. In phase 2 (n=6440), serosurveillance was done among 1299 (93·4%) of 1391 health-care workers reporting symptoms, and in a subset of asymptomatic health-care workers (405 [8·0%] of 5049). There was variation in test performance between the lateral flow serological assays; however, the Encode assay displayed reasonable IgG sensitivity (127 of 136; 93·4% [95% CI 87·8-96·9]) and specificity (99 of 100; 99·0% [94·6-100·0]) among PCR-proven cases and good agreement (282 of 300; 94·0% [91·3-96·7]) with the laboratory immunoassay. By contrast, the Onsite assay had reduced sensitivity (120 of 136; 88·2% [95% CI 81·6-93·1]) and specificity (94 of 100; 94·0% [87·4-97·8]) and agreement (254 of 300; 84·7% [80·6-88·7]). Five (7%) of 70 PCR-positive cases were negative across all assays. Late changes in lateral flow serological assay bands were recorded in 74 (9·3%) of 800 cassettes (35 [8·8%] of 400 Encode assays; 39 [9·8%] of 400 Onsite assays), but only seven (all Onsite assays) of these changes were concordant with the laboratory immunoassay. In phase 2, seroprevalence among the workforce was estimated to be 10·6% (95% CI 7·6-13·6) in asymptomatic health-care workers and 44·7% (42·0-47·4) in symptomatic health-care workers. Seroprevalence across the entire workforce was estimated at 18·0% (95% CI 17·0-18·9). Although a good positive predictive value was observed with both lateral flow serological assays and ELISA, this agreement only occurred if the pre-test probability was modified by a strict clinical case definition. Late development of lateral flow serological assay bands would preclude postal strategies and potentially home testing. Identification of false-negative results among health-care workers across all assays suggest caution in interpretation of IgG results at this stage; for now, testing is perhaps best delivered in a clinical setting, supported by government advice about physical distancing. None.

Pallett SJC ，Rayment M ，Patel A ，Fitzgerald-Smith SAM ，Denny SJ ，Charani E ，Mai AL ，Gilmour KC ，Hatcher J ，Scott C ，Randell P ，Mughal N ，Jones R ，Moore LSP ，Davies GW ... -  《-》

Evaluation of the EUROIMMUN Anti-SARS-CoV-2 ELISA Assay for detection of IgA and IgG antibodies.

As the Coronavirus 2019 (COVID-19) pandemic evolves, the development of immunoassays to help determine exposure and potentially predict immunity has become a pressing priority. In this report we present the performance of the EUROIMMUN enzyme-linked immunosorbent assay (ELISA) for semi-quantitative detection of IgA and IgG antibodies in serum and plasma samples using recombinant S1 domain of the SARS-CoV-2 spike protein as antigen. Specimens from patients, with and without COVID-19 infection, were tested at the University of Chicago Clinical Microbiology and Immunology Laboratory. Of 86 samples from SARS-CoV-2 PCR-negative patients, including 28 samples positive for common human coronavirus strains, 76 tested negative and 10 tested positive for IgA (88.4% agreement, 95% CI: 79.9-93.6) while 84 tested negative and 2 tested positive for IgG (97.7% agreement, 95% CI: 91.9-99.6). Of 82 samples from SARS-CoV-2 PCR-positive patients, 14 tested negative and 68 tested positive for IgA (82.9% agreement, 95% CI: 73.4-89.5) while 27 tested negative and 55 tested positive for IgG (67.1% agreement, 95% CI: 56.3-76.3). Of samples collected ≥4 days after positive PCR, 38 of 42 (90.5% agreement, 95% CI: 77.9-96.2) were positive for IgA, and 42 of 42 (100% agreement, 95% CI: 91.6-100) were positive for IgG, respectively. The EUROIMMUN Anti-SARS-CoV-2 ELISA Assay demonstrated good sensitivity for detection of IgA and excellent sensitivity for detection of IgG antibodies from samples collected ≥4 days, after COVID-19 diagnosis by PCR. This assay demonstrated good specificity for IgA and excellent specificity for IgG and demonstrated only borderline cross reaction in 2 of the 28 samples from patients with common human coronaviruses infection, types NL63 and OC43.

Beavis KG ，Matushek SM ，Abeleda APF ，Bethel C ，Hunt C ，Gillen S ，Moran A ，Tesic V ... -  《-》

Epidemiology of SARS-CoV-2 antibodies among firefighters/paramedics of a US fire department: a cross-sectional study.

We estimate the point seroprevalence of SARS-CoV-2 antibodies in the frontline firefighter/paramedic workforce of a South Florida fire department located in the epicentre of a State outbreak. A cross-sectional study design was used to estimate the point seroprevalence of SARS-CoV-2 antibodies using a rapid immunoglobulin (Ig)M-IgG combined point-of-care lateral flow immunoassay among frontline firefighters/paramedics collected over a 2-day period, 16-17 April 2020. Fire department personnel were emailed a survey link assessing COVID-19 symptoms and work exposures the day prior to the scheduled drive-through antibody testing at a designated fire station. Off-duty and on-duty firefighter/paramedic personnel drove through the fire station/training facility in their personal vehicles or on-duty engine/rescue trucks for SARS-CoV-2 antibody testing. Among the 203 firefighters/paramedics that make up the fire department workforce, 18 firefighters/paramedics (8.9%) tested positive for SARS-CoV-2 antibodies, of which 8 firefighters/paramedics (3.9%) were IgG positive only, 8 (3.9%) were IgM positive only and 2 (0.1%) were IgG/IgM positive. The positive predictive value (PPV) of the serological test is estimated to be 33.2% and the negative predictive value is 99.3%. The average number of COVID-19 case contacts (ie, within 6 feet of an infected person (laboratory-confirmed or probable COVID-19 patient) for ≥15 min) experienced by firefighters/paramedics was higher for those with positive serology compared with those with negative (13.3 cases vs 7.31 cases; p=0.022). None of the antibody positive firefighters/paramedics reported receipt of the annual influenza vaccine compared with firefighters/paramedics who tested negative for SARS-CoV-2 antibodies (0.0% vs 21.0%; p=0.027). Rapid SARS-CoV-2 IgM-IgG antibody testing documented early-stage and late-stage infection in a firefighter workforce providing insight to a broader medical surveillance project on return to work for firefighters/paramedics. Given the relatively low PPV of the serological test used in this study back in April 2020, caution should be used in interpreting test results.

Caban-Martinez AJ ，Schaefer-Solle N ，Santiago K ，Louzado-Feliciano P ，Brotons A ，Gonzalez M ，Issenberg SB ，Kobetz E ... -  《-》