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3.
J Med Virol ; 93(12): 6686-6692, 2021 Dec.
Article in English | MEDLINE | ID: covidwho-1544320

ABSTRACT

To control the spread of the coronavirus disease 2019 (COVID-19) epidemics, it is necessary to have easy-to-use, reliable diagnostic tests available. The nasopharyngeal sampling method being often uncomfortable, nasal sampling could prove to be a viable alternative to the reference sampling method. We performed a multicentre, prospective validation study of the COVID-VIRO® test, using a nasal swab sampling method, in a point-of-care setting. In addition, we performed a multicentre, prospective, and usability study to validate the use of the rapid antigen nasal diagnostic test by laypersons. In March 2021, 239 asymptomatic and symptomatic patients were included in the validation study. Compared with reverse-transcription polymerase chain reaction on nasopharyngeal samples, the sensitivity and specificity of the COVID-VIRO® Antigen test combined with a nasal sampling method were evaluated as 96.88% and 100%, respectively. A total of 101 individuals were included in the usability study. Among these, 99% of the participants rated the instructions material as good, 98% of the subjects executed the test procedure well, and 98% of the participants were able to correctly interpret the test results. This study validates the relevance of COVID-VIRO® as a diagnostic tool from nasal specimens as well as its usability in the general population. COVID-VIRO® diagnostic performances and ease of use make it suitable for widespread utilization.


Subject(s)
COVID-19 Testing/methods , Diagnostic Tests, Routine/methods , Self-Testing , Adult , Antigens, Viral/blood , Humans , Male , Point-of-Care Testing , Prospective Studies , SARS-CoV-2/immunology , Sensitivity and Specificity
4.
Anal Biochem ; 631: 114360, 2021 10 15.
Article in English | MEDLINE | ID: covidwho-1474246

ABSTRACT

To monitor the levels of protecting antibodies raised in the population in response to infection and/or to immunization with SARS-CoV-2, we need a technique that allows high throughput and low-cost quantitative analysis of human IgG antibodies reactive against viral antigens. Here we describe an ultra-fast, high throughput and inexpensive assay to detect SARS-CoV-2 seroconversion in humans. The assay is based on Ni2+ magnetic particles coated with His tagged SARS-CoV-2 antigens. A simple and inexpensive 96 well plate magnetic extraction/homogenization process is described which allows the simultaneous analysis of 96 samples and delivers results in 7 min with high accuracy.


Subject(s)
Antibodies, Viral/blood , COVID-19 Serological Testing/methods , COVID-19/diagnosis , Immunoglobulin G/blood , SARS-CoV-2/isolation & purification , Antibodies, Viral/immunology , Antigens, Viral/blood , Antigens, Viral/immunology , COVID-19/blood , COVID-19/immunology , COVID-19 Serological Testing/economics , Enzyme-Linked Immunosorbent Assay/economics , Enzyme-Linked Immunosorbent Assay/methods , Humans , Immunoglobulin G/immunology , Magnets/chemistry , Nickel/chemistry , SARS-CoV-2/immunology , Sensitivity and Specificity , Seroconversion , Time Factors
5.
Anal Bioanal Chem ; 413(29): 7251-7263, 2021 Dec.
Article in English | MEDLINE | ID: covidwho-1460298

ABSTRACT

Supply shortage for the development and production of preventive, therapeutic, and diagnosis tools during the COVID-19 pandemic is an important issue affecting the wealthy and poor nations alike. Antibodies and antigens are especially needed for the production of immunological-based testing tools such as point-of-care tests. Here, we propose a simple and quick magnetic nanoparticle (MNP)-based separation/isolation approach for the repurposing of infected human samples to produce specific antibodies and antigen cocktails. Initially, an antibody cocktail was purified from serums via precipitation and immunoaffinity chromatography. Purified antibodies were conjugated onto MNPs and used as an affinity matrix to separate antigens. The characterization process was performed by ELISA, SDS-PAGE, electrochemistry, isothermal titration calorimetry, and LC-Q-TOF-MS/MS analyses. The MNP-separated peptides can be used for mass spectrometry-based as well as paper-based lateral flow assay diagnostic. The exploitation of the current workflow for the development of efficient diagnostic tools, specific treatments, and fundamental research can significantly impact the present or eventual pandemic. This workflow can be considered as a two birds, one stone-like strategy.


Subject(s)
Antibodies, Viral/isolation & purification , Antigens, Viral/isolation & purification , COVID-19/diagnosis , Cost-Benefit Analysis , Immunoassay/economics , SARS-CoV-2/isolation & purification , Viremia/virology , Antibodies, Viral/blood , Antigens, Viral/blood , COVID-19/virology , Calorimetry , Electrophoresis, Polyacrylamide Gel , Enzyme-Linked Immunosorbent Assay , Humans , SARS-CoV-2/immunology , Specimen Handling , Tandem Mass Spectrometry , Viremia/blood , Workflow
6.
Front Immunol ; 12: 739037, 2021.
Article in English | MEDLINE | ID: covidwho-1448729

ABSTRACT

Background: Transfusion of COVID-19 convalescent plasma (CCP) containing high titers of anti-SARS-CoV-2 antibodies serves as therapy for COVID-19 patients. Transfusions early during disease course was found to be beneficial. Lessons from the SARS-CoV-2 pandemic could inform early responses to future pandemics and may continue to be relevant in lower resource settings. We sought to identify factors correlating to high antibody titers in convalescent plasma donors and understand the magnitude and pharmacokinetic time course of both transfused antibody titers and the endogenous antibody titers in transfused recipients. Methods: Plasma samples were collected up to 174 days after convalescence from 93 CCP donors with mild disease, and from 16 COVID-19 patients before and after transfusion. Using ELISA, anti-SARS-CoV-2 Spike RBD, S1, and N-protein antibodies, as well as capacity of antibodies to block ACE2 from binding to RBD was measured in an in vitro assay. As an estimate for viral load, viral RNA and N-protein plasma levels were assessed in COVID-19 patients. Results: Anti-SARS-CoV-2 antibody levels and RBD-ACE2 blocking capacity were highest within the first 60 days after symptom resolution and markedly decreased after 120 days. Highest antibody titers were found in CCP donors that experienced fever. Effect of transfused CCP was detectable in COVID-19 patients who received high-titer CCP and had not seroconverted at the time of transfusion. Decrease in viral RNA was seen in two of these patients. Conclusion: Our results suggest that high titer CCP should be collected within 60 days after recovery from donors with past fever. The much lower titers conferred by transfused antibodies compared to endogenous production in the patient underscore the importance of providing CCP prior to endogenous seroconversion.


Subject(s)
COVID-19/therapy , Convalescence , SARS-CoV-2/immunology , Seroconversion , Adult , Antibodies, Neutralizing/blood , Antibodies, Neutralizing/immunology , Antibodies, Viral/blood , Antibodies, Viral/immunology , Antigens, Viral/blood , Blood Donors , COVID-19/blood , COVID-19/immunology , Female , Humans , Immunization, Passive , Kinetics , Male , Middle Aged , Outpatients , RNA, Viral/blood
8.
J Med Virol ; 94(1): 222-228, 2022 01.
Article in English | MEDLINE | ID: covidwho-1372751

ABSTRACT

The current study aimed at characterizing the dynamics of SARS-CoV-2 nucleocapsid (N) antigenemia in a cohort of critically ill adult COVID-19 patients and assessing its potential association with plasma levels of biomarkers of clinical severity and mortality. Seventy-three consecutive critically ill COVID-19 patients (median age, 65 years) were recruited. Serial plasma (n = 340) specimens were collected. A lateral flow immunochromatography assay and reverse-transcription polymerase chain reaction (RT-PCR) were used for SARS-CoV-2 N protein detection and RNA quantitation and in plasma, respectively. Serum levels of inflammatory and tissue-damage biomarkers in paired specimens were measured. SARS-CoV-RNA N-antigenemia and viral RNAemia were documented in 40.1% and 35.6% of patients, respectively at a median of 9 days since symptoms onset. The level of agreement between the qualitative results returned by the N-antigenemia assay and plasma RT-PCR was moderate (k = 0.57; p < 0.0001). A trend towards higher SARS-CoV-2 RNA loads was seen in plasma specimens testing positive for N-antigenemia assay than in those yielding negative results (p = 0.083). SARS-CoV-2 RNA load in tracheal aspirates was significantly higher (p < 0.001) in the presence of concomitant N-antigenemia than in its absence. Significantly higher serum levels of ferritin, lactose dehydrogenase, C-reactive protein, and D-dimer were quantified in paired plasma SARS-CoV-2 N-positive specimens than in those testing negative. Occurrence of SARS-CoV-2 N-antigenemia was not associated with increased mortality in univariate logistic regression analysis (odds ratio, 1.29; 95% confidence interval, 0.49-3.34; p = 0.59). In conclusion, SARS-CoV-2 N-antigenemia detection is relatively common in ICU patients and appears to associate with increased serum levels of inflammation and tissue-damage markers. Whether this virological parameter may behave as a biomarker of poor clinical outcome awaits further investigations.


Subject(s)
COVID-19/virology , Coronavirus Nucleocapsid Proteins/blood , Critical Illness , SARS-CoV-2 , Adult , Aged , Aged, 80 and over , Antigens, Viral/blood , Biomarkers/analysis , Biomarkers/blood , COVID-19/mortality , Coronavirus Nucleocapsid Proteins/immunology , Female , Humans , Inflammation , Male , Middle Aged , Phosphoproteins/blood , Phosphoproteins/immunology , Prospective Studies , RNA, Viral/analysis , RNA, Viral/blood , SARS-CoV-2/genetics , SARS-CoV-2/immunology , SARS-CoV-2/isolation & purification , Trachea/virology , Young Adult
9.
JCI Insight ; 6(15)2021 08 09.
Article in English | MEDLINE | ID: covidwho-1350084

ABSTRACT

A subset of COVID-19 patients exhibit post-acute sequelae of COVID-19 (PASC), but little is known about the immune signatures associated with these syndromes. We investigated longitudinal peripheral blood samples in 50 individuals with previously confirmed SARS-CoV-2 infection, including 20 who experienced prolonged duration of COVID-19 symptoms (lasting more than 30 days; median = 74 days) compared with 30 who had symptom resolution within 20 days. Individuals with prolonged symptom duration maintained antigen-specific T cell response magnitudes to SARS-CoV-2 spike protein in CD4+ and circulating T follicular helper cell populations during late convalescence, while those without persistent symptoms demonstrated an expected decline. The prolonged group also displayed increased IgG avidity to SARS-CoV-2 spike protein. Significant correlations between symptom duration and both SARS-CoV-2-specific T cells and antibodies were observed. Activation and exhaustion markers were evaluated in multiple immune cell types, revealing few phenotypic differences between prolonged and recovered groups, suggesting that prolonged symptom duration is not due to persistent systemic inflammation. These findings demonstrate that SARS-CoV-2-specific immune responses are maintained in patients suffering from prolonged post-COVID-19 symptom duration in contrast to those with resolved symptoms and may suggest the persistence of viral antigens as an underlying etiology.


Subject(s)
COVID-19/immunology , SARS-CoV-2/immunology , Adult , Aged , Aged, 80 and over , Antibodies, Viral/blood , Antibodies, Viral/immunology , Antigens, Viral/blood , Antigens, Viral/immunology , COVID-19/blood , Female , Humans , Immunity , Immunity, Cellular , Male , Middle Aged , Spike Glycoprotein, Coronavirus/blood , Spike Glycoprotein, Coronavirus/immunology , T-Lymphocytes/immunology , Young Adult
11.
Mikrochim Acta ; 188(8): 262, 2021 07 20.
Article in English | MEDLINE | ID: covidwho-1317559

ABSTRACT

COVID-19 is now a severe threat to global health. Facing this pandemic, we developed a space-encoding microfluidic biochip for high-throughput, rapid, sensitive, simultaneous quantitative detection of SARS-CoV-2 antigen proteins and IgG/IgM antibodies in serum. The proposed immunoassay biochip integrates the advantages of graphene oxide quantum dots (GOQDs) and microfluidic chip and is capable of conducting multiple SARS-CoV-2 antigens or IgG/IgM antibodies of 60 serum samples simultaneously with only 2 µL sample volume of each patient. Fluorescence intensity of antigens and IgG antibody detection at emission wavelength of ~680 nm was used to quantify the target concentration at excitation wavelength of 632 nm, and emission wavelength of ~519 nm was used during the detection of IgM antibodies at excitation wavelength of 488 nm. The method developed has a large linear quantification detection regime of 5 orders of magnitude, an ultralow detection limit of ~0.3 pg/mL under optimized conditions, and less than 10-min qualitative detection time. The proposed biosensing platform will not only greatly facilitate the rapid diagnosis of COVID-19 patients, but also provide a valuable screening approach for infected patients, medical therapy, and vaccine recipients.


Subject(s)
Antigens, Viral/blood , Immunoassay , Immunoglobulin G/blood , Immunoglobulin M/blood , SARS-CoV-2/isolation & purification , Antigen-Antibody Reactions , Antigens, Viral/immunology , Humans , Immunoglobulin G/immunology , Immunoglobulin M/immunology , Nanoparticles/chemistry , Particle Size , SARS-CoV-2/immunology , Sensitivity and Specificity
12.
J Clin Invest ; 131(14)2021 07 15.
Article in English | MEDLINE | ID: covidwho-1311202

ABSTRACT

BACKGROUNDWeeks after SARS-CoV-2 infection or exposure, some children develop a severe, life-threatening illness called multisystem inflammatory syndrome in children (MIS-C). Gastrointestinal (GI) symptoms are common in patients with MIS-C, and a severe hyperinflammatory response ensues with potential for cardiac complications. The cause of MIS-C has not been identified to date.METHODSHere, we analyzed biospecimens from 100 children: 19 with MIS-C, 26 with acute COVID-19, and 55 controls. Stools were assessed for SARS-CoV-2 by reverse transcription PCR (RT-PCR), and plasma was examined for markers of breakdown of mucosal barrier integrity, including zonulin. Ultrasensitive antigen detection was used to probe for SARS-CoV-2 antigenemia in plasma, and immune responses were characterized. As a proof of concept, we treated a patient with MIS-C with larazotide, a zonulin antagonist, and monitored the effect on antigenemia and the patient's clinical response.RESULTSWe showed that in children with MIS-C, a prolonged presence of SARS-CoV-2 in the GI tract led to the release of zonulin, a biomarker of intestinal permeability, with subsequent trafficking of SARS-CoV-2 antigens into the bloodstream, leading to hyperinflammation. The patient with MIS-C treated with larazotide had a coinciding decrease in plasma SARS-CoV-2 spike antigen levels and inflammatory markers and a resultant clinical improvement above that achieved with currently available treatments.CONCLUSIONThese mechanistic data on MIS-C pathogenesis provide insight into targets for diagnosing, treating, and preventing MIS-C, which are urgently needed for this increasingly common severe COVID-19-related disease in children.


Subject(s)
COVID-19/etiology , COVID-19/physiopathology , Haptoglobins/physiology , Intestinal Mucosa/physiopathology , Protein Precursors/physiology , SARS-CoV-2 , Systemic Inflammatory Response Syndrome/etiology , Systemic Inflammatory Response Syndrome/physiopathology , Adolescent , Antigens, Viral/blood , Biomarkers/blood , COVID-19/virology , Case-Control Studies , Child , Child, Preschool , Female , Haptoglobins/antagonists & inhibitors , Humans , Infant , Infant, Newborn , Intestinal Mucosa/drug effects , Intestinal Mucosa/virology , Male , Oligopeptides/pharmacology , Permeability/drug effects , Proof of Concept Study , Protein Precursors/antagonists & inhibitors , Protein Precursors/blood , SARS-CoV-2/immunology , SARS-CoV-2/pathogenicity , Spike Glycoprotein, Coronavirus/blood , Spike Glycoprotein, Coronavirus/immunology , Systemic Inflammatory Response Syndrome/virology , Young Adult
13.
Ann Ig ; 33(5): 518-520, 2021.
Article in English | MEDLINE | ID: covidwho-1296186

ABSTRACT

Abstract: Out of 38,282 passengers entering Italy at a major seaport, submitted to SARS-CoV-2 rapid antigenic test, 272 (0.6%) resulted positive and 212 (93.4%) were confirmed positive by qRT-PCR, leaving a 0.6% of false positive. Those resident in the area under control of the same Local Health Authority of the seaport were immediately submitted to isolation and investigated for contact tracing, the others notified to their Local Health Authority which did the same in the following day. This procedure was made possible by a full-time dedication of the local healthcare workers who managed all the passengers disembarking around the clock along the months of the emergency.


Subject(s)
Antigens, Viral/blood , COVID-19 Testing , COVID-19/prevention & control , Mass Screening/organization & administration , SARS-CoV-2/isolation & purification , Travel , Adult , COVID-19/diagnosis , COVID-19 Nucleic Acid Testing , Contact Tracing , Female , Health Personnel , Humans , Italy , Male , Middle Aged , Nasopharynx/virology , Retrospective Studies , SARS-CoV-2/immunology , Ships , Socioeconomic Factors , Travel-Related Illness
14.
J Virol Methods ; 296: 114222, 2021 10.
Article in English | MEDLINE | ID: covidwho-1290729

ABSTRACT

BACKGROUND: Spike protein domains are being used in various serology-based assays to detect prior exposure to SARS-CoV-2 virus. However, there has been limited comparison of antibody titers against various spike protein antigens among COVID-19 infected patients. METHODS: We compared four spike proteins (RBD, S1, S2 and a stabilized spike trimer (ST)) representing commonly used antigens for their reactivity to human IgG antibodies using indirect ELISA in serum from COVID-19 patients and pre-2020 samples. ST ELISA was also compared against the EUROIMMUN IgG ELISA test. Further, we estimated time appropriate IgG and IgA seropositivity rates in COVID-19 patients using a panel of sera samples collected longitudinally from the day of onset of symptoms (DOS). RESULTS: Among the four spike antigens tested, the ST demonstrated the highest sensitivity (86.2 %; 95 % CI: 77.8-91.7 %), while all four antigens showed high specificity to COVID-19 sera (94.7-96.8 %). 13.8 % (13/94) of the samples did not show seroconversion in any of the four antigen-based assays. In a double-blinded head-to-head comparison, ST based IgG ELISA displayed a better sensitivity (87.5 %, 95 % CI: 76.4-93.8 %) than the EUROIMMUN IgG ELISA (67.9 %, 95 % CI: 54.8-78.6 %). Further, in ST-based assays, we found 48 % and 50 % seroconversion in the first six days (from DOS) for IgG and IgA antibodies, respectively, which increased to 84 % (IgG) and 85 % (IgA) for samples collected ≥22 days from DOS. CONCLUSIONS: Comparison of spike antigens demonstrates that spike trimer protein is a superior option as an ELISA antigen for COVID-19 serology.


Subject(s)
Antigens, Viral/immunology , COVID-19 Serological Testing/methods , COVID-19/diagnosis , SARS-CoV-2/immunology , Spike Glycoprotein, Coronavirus/immunology , Antibodies, Viral/blood , Antibodies, Viral/immunology , Antigens, Viral/blood , COVID-19/blood , COVID-19/immunology , Enzyme-Linked Immunosorbent Assay/methods , Humans , Immunoglobulin A/blood , Immunoglobulin A/immunology , Immunoglobulin G/blood , Immunoglobulin G/immunology , Sensitivity and Specificity , Seroconversion
15.
Viruses ; 13(6)2021 06 14.
Article in English | MEDLINE | ID: covidwho-1270128

ABSTRACT

Humoral immunity has emerged as a vital immune component against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Nevertheless, a subset of recovered Coronavirus Disease-2019 (COVID-19) paucisymptomatic/asymptomatic individuals do not generate an antibody response, constituting a paradox. We assumed that immunodiagnostic assays may operate under a competitive format within the context of antigenemia, potentially explaining this phenomenon. We present a case where persistent antigenemia/viremia was documented for at least 73 days post-symptom onset using 'in-house' methodology, and as it progressively declined, seroconversion took place late, around day 55, supporting our hypothesis. Thus, prolonged SARS-CoV-2 antigenemia/viremia could mask humoral responses, rendering, in certain cases, the phenomenon of 'non-responders' a misnomer.


Subject(s)
Antibodies, Viral/blood , Antigens, Viral/blood , Antigens, Viral/immunology , COVID-19 Serological Testing/standards , COVID-19/diagnosis , SARS-CoV-2/immunology , Antibodies, Viral/metabolism , Antigens, Viral/metabolism , Binding Sites, Antibody , COVID-19/blood , COVID-19/immunology , COVID-19/virology , COVID-19 Serological Testing/statistics & numerical data , Humans , Immunity, Humoral/immunology , Immunoglobulin G/blood , Male , Sensitivity and Specificity , Seroconversion , Young Adult
19.
J Med Virol ; 93(5): 3069-3076, 2021 05.
Article in English | MEDLINE | ID: covidwho-1196539

ABSTRACT

The implementation of rapid diagnostic tests (RDTs) may enhance the efficiency of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) testing, as RDTs are widely accessible and easy to use. The aim of this study was to evaluate the performance of a diagnosis strategy based on a combination of antigen and immunoglobulin M (IgM) or immunoglobulin G (IgG) serological RDTs. Plasma and nasopharyngeal samples were collected between 14 March and 11 April 2020 at hospital admission from 45 patients with reverse transcription polymerase chain reaction (RT-PCR) confirmed COVID-19 and 20 negative controls. SARS-CoV-2 antigen (Ag) was assessed in nasopharyngeal swabs using the Coris Respi-Strip. For IgM/IgG detection, SureScreen Diagnostics and Szybio Biotech RDTs were used in addition to laboratory assays (Abbott Alinity i SARS-CoV-2 IgG and Theradiag COVID-19 IgM enzyme-linked immunosorbent assay). Using the Ag RDT, 13 out of 45 (29.0%) specimens tested positive, the sensitivity was 87.0% for cycle threshold (Ct ) values ≤25% and 0% for Ct values greater than 25. IgG detection was associated with high Ct values and the amount of time after the onset of symptoms. The profile of isolated IgM on RDTs was more frequently observed during the first and second week after the onset of symptoms. The combination of Ag and IgM/IgG RDTs enabled the detection of up to 84.0% of COVID-19 confirmed cases at hospital admission. Antigen and antibody-based RDTs showed suboptimal performances when used alone. However when used in combination, they are able to identify most COVID-19 patients admitted in an emergency department.


Subject(s)
Antibodies, Viral/blood , Antigens, Viral/blood , COVID-19 Serological Testing/methods , COVID-19/diagnosis , SARS-CoV-2/isolation & purification , Adult , Aged , Aged, 80 and over , COVID-19/virology , Enzyme-Linked Immunosorbent Assay , Female , Hospitalization , Humans , Immunoglobulin G/blood , Immunoglobulin M/blood , Male , Middle Aged , Nasopharynx/virology , Reverse Transcriptase Polymerase Chain Reaction/methods , Serologic Tests/methods
20.
Biosci Trends ; 15(2): 93-99, 2021 May 11.
Article in English | MEDLINE | ID: covidwho-1154737

ABSTRACT

As the COVID-19 epidemic is still ongoing, a more rapid detection of SARS-CoV-2 infection such as viral antigen-detection needs to be evaluated for early diagnosis of COVID-19 disease. Here, we report the dynamic changes of SARS-CoV-2 viral antigens in nasopharyngeal swabs of COVID-19 patients and its association with the viral nucleic acid clearance and clinical outcomes. Eighty-five COVID-19 patients were enrolled for detection of SARS-CoV-2 viral antigens, including 57 anti-SARS-CoV-2 antibody negative cases and 28 antibody positive cases. The viral antigen could be detected in 52.63% (30/57) patients with SARS-CoV-2 antibody negative at the early stage of SARS-CoV-2 infection, especially in the first 5 days after disease onset (p = 0.0018) and disappeared in about 8 days after disease onset. Viral antigens were highly detectable in patients with low Ct value (less than 30) of SARS-CoV-2 nucleic acid RT-PCT assay, suggesting the expression of viral antigen was associated with high viral load. Furthermore, positive antigen detection indicated disease progression, nine cases with positive antigen (9/30, 30.0%), in contrast to two cases (2/27, 7.40%) (p = 0.0444) with negative antigen, which progressed into severe disease. Thus, the viral antigens were persistent in early stages of infection when virus was in highly replicating status, and viral antigen detection promises to rapidly screen positive patients in the early stage of SARS-CoV-2 infection.


Subject(s)
Antigens, Viral/analysis , COVID-19 Testing/methods , COVID-19/diagnosis , SARS-CoV-2/immunology , Adolescent , Adult , Aged , Antigens, Viral/blood , COVID-19/immunology , COVID-19/virology , COVID-19 Nucleic Acid Testing , COVID-19 Serological Testing , COVID-19 Testing/trends , China/epidemiology , Disease Progression , Early Diagnosis , False Negative Reactions , Female , Humans , Male , Middle Aged , Nasopharynx/immunology , Nasopharynx/virology , Pandemics , SARS-CoV-2/genetics , SARS-CoV-2/isolation & purification , Time Factors , Viral Load , Young Adult
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