DOI: https://doi.org/10.21203/rs.3.rs-1661025/v1
The severe acute respiratory syndrome coronavirus (SARS-CoV-2) infection originated from China in December 2019 and rapidly spread worldwide. SARS-CoV-2 posed a major challenge for global public health. It is well known that SARS-CoV-2 infection is followed by an immune response and formation of antibodies. Thus, determination of infection seroprevalence can provide important information on SARS-CoV-2 and contribute to proper organization of public health measures. Our study aimed to investigate the possibility of rapid tests application for determination of seroprevalence of SARS-CoV-2 infection.
70 serum samples with determined IgG against nucleocapsid protein of SARS-CoV-2 by enzyme linked immunoassay (ELISA) method were tested by application of rapid immunochromatographic test for the qualitative detection of IgG antibodies to SARS-CoV-2. It has been revealed that by both methods: a) 21 (77.8%) samples are negatives; b) 23 (67.7%) samples are positive; and c) 3 (33.3%) equivocal by ELISA method samples are positive by rapid test, although 6 (66.7%) equivocal by ELISA method samples are negative by rapid test. By consideration of these data we assumed that rapid test for qualitative detection of IgG antibodies to SARS-CoV-2 can be used as screening method for determination of seroprevalence of SARS-CoV-2 infection.
In case of SARS-CoV-2 induced global pandemics the initial surveillance has been primarily focused on those individuals who were hospitalized with severe disease and those who reported symptoms. As an outcome, the estimates of the infection in the population were struggled to account mild or asymptomatic cases of infection that did not require medical care. This has been exacerbated by availability of diagnostical tests for identification of acute infection as well as limited capacity for testing [1]. The need for seroprevalence studies to determine the infection prevalence through performance of population-based serological surveys is obvious [2, 3]. Identification of knowledge and methodological gaps in the context of SARS-CoV-2 induced situation is of high importance for public health development and preparedness for possible future global health crisis. To address this question, we initiated the study aimed to evaluate the possibility of rapid immunochromatographic test for qualitative detection of IgG antibodies to SARS-CoV-2 application as the screening method for determination of seroprevalence of SARS-CoV-2 infection. As an indicator of the mentioned infection seroprevalence there were used the quantitative values of IgG against viral nucleocapsid protein of SARS-CoV-2. The nucleocapsid protein of the virus is a multivalent RNA-binding protein which is critical for viral replication and genome packaging [4]. It has been reported that the detection of the IgG against nucleocapsid protein to SARS-CoV-2 is more sensitive seroprevalence indicator than antibody against spike protein in COVID-19 cases [5].
In this study were used 70 samples with determined IgG against nucleocapsid protein of SARS-CoV-2 by enzyme linked immunoassay (ELISA) method. For determination of this antibody there were used the NovaLisa SARS-CoV-2 (COVID-19) IgG ELISA diagnostical kit (NovaTec Immunodiagnostica GmbH, Germany). According to the manufacturer this kit’s specificity is 99.53% and the analytical sensitivity is defined as the probability of the assay of scoring positive in the presence of the specific analyte. 27 samples out of the mentioned 70 ones were negative for IgG against nucleocapsid protein of SARS-CoV-2, 34 samples out of the mentioned 70 – positive, 9 samples – equivocal.
All 70 samples were tested by usage of AMP rapid test SARS-CoV-2 IgG qualitative test (AMEDA Labordiagnostik GmbH, Austria). This is the rapid immunochromatographic test for the qualitative detection of IgG antibodies to SARS-CoV-2 in human samples (whole blood, serum, plasma). The test has been performed by applying the serum sample to the sample well of the cassette and observation of the colored lines formation. IgG antibodies to SARS-CoV-2 were detected by utilizing a combination of anti-human IgG, recombinant SARS-CoV-2 antigens conjugated with colloid gold, rabbit IgG gold conjugates as well as a goat anti-rabbit IgG in the control region. The sample migrated by capillary effect along the membrane. IgG antibodies to SARS-CoV-2 bind to SARS-CoV-2 conjugate and captured by anti-human IgG with the formation of a colored line in test region. The presence of the colored line in test region indicated a positive result; the absence of it – negative result. As a procedure control a colored line appeared in the control region; this line confirmed that sufficient sample has been absorbed.
By application of the rapid test for IgG of SARS-CoV-2 32 (45.7%) samples were reported as positive, 38 (54.3%) samples – as negative. It has been revealed that: a) in case 34 positive by ELISA method samples 23 (67.7%) were interpreted as positive and 11 (32.3%) – as negative; b) among 27 negative by ELISA method samples 21 (77.8%) samples are negative and 6 (22.2%) ones were interpreted as positive; c) among 9 equivocal by ELISA method samples 3 (33.3%) were reported as positive and 6 (66.7%) samples – as negative (Table 1).
| Rapid test ELISA | Positive | Negative |
|---|---|---|
| Positive (> 11 NTU), 34 (48.5%) samples | 23 (67.7%) samples | 11 (32.3%) samples |
| Negative (< 9 NTU), 27 (38.6%) samples | 6 (22.2%) samples | 21 (77.8%) samples |
| Equivocal (9–11 NTU), 9 (12.9%) samples | 3 (33.3%) samples | 6 (66.7%) samples |
It has been revealed that in 6 samples reported as the negative by rapid test for IgG of SARS-CoV-2 the quantity of IgG against nucleocapsid protein detected by ELISA method is lower than 17 NTU, in rest 5 samples the quantity of IgG against nucleocapsid protein detected by ELISA method varies in range 18–31 NTU. In case of 6 samples reported as positive by rapid test for IgG of SARS-CoV-2 the quantity of IgG against nucleocapsid protein detected by ELISA varies in range 6–8 NTU. Findings suggest that all samples presenting the difference of rapid test and ELISA method results the further investigation should be performed. Although by consideration of the present study data it can be assumed that rapid test for IgG of SARS-CoV-2 can be used as the possible method of screening of seroprevalence of SARS-CoV-2 infection. Such approach will be helpful for the preliminary estimation of the infection spread in the population with attention and focus on mild and asymptomatic cases of SARS-CoV-2 too.
Limitations
The study has been performed on a small number of samples.
The study has been performed by usage of a single rapid test.
The study has been performed without consideration of SARS-CoV-2 polymerase chain reaction data specific tot he samples.
The study aimimng determonation of IgG against nucleocapsid protein detected by ELISA method has been approved by the Bioethics Committee of the Petre Shotadze Tbilisi Medical Academy. All procedures performed in this study were in accordance with the Helsinki Declaration of 1975, as revised in 2013. Although the ethics approval and concent to participate is not applicable fort he study the data of which are presented in the present manuscript.
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Data sharing is not applicable to this article as no datasets were generated or analysed during the current study.
The authors declare that they have no competing interests.
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SI performed experimental activities and data analysis; TS organized and performed samples collection; ML organized technical issues of experimental activities; EK contributes study performance and manuscript preparation. All authors read and approved the final manuscript.
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