key: cord-0708481-qe4kccv6
authors: Wu, Xianyong; Chen, Qiming; Li, Junhai; Liu, Zhanmin
title: Diagnostic techniques for COVID-19: A mini-review
date: 2021-12-18
journal: J Virol Methods
DOI: 10.1016/j.jviromet.2021.114437
sha: fc2f604a75052163c40136d925717ac09d15fa28
doc_id: 708481
cord_uid: qe4kccv6

COVID-19, a new respiratory infectious disease, was first reported at the end of 2019, in Wuhan, China. Now, COVID-19 is still causing major loss of human life and economic productivity in almost all countries around the world. Early detection, early isolation, and early diagnosis of COVID-19 patients and asymptomatic carriers are essential to blocking the spread of the pandemic. This paper briefly reviewed COVID-19 diagnostic assays for clinical application, including nucleic acid tests, immunological methods, and Computed Tomography (CT) imaging. Nucleic acid tests (NAT) target the virus genome and indicates the existence of the SARS-CoV-2 virus. Currently, real-time quantitative PCR (qPCR) is the most widely used NAT and, basically, is the most used diagnostic assay for COVID-19. Besides qPCR, many novel rapid and sensitive NAT assays were also developed. Serological testing (detection of serum antibodies specific to SARS-CoV-2), which belongs to the immunological methods, is also used in the diagnosis of COVID-19. The positive results of serological testing indicate the presence of antibodies specific to SARS-CoV-2 resulting from being infected with the virus. Viral antigen detection assays are also important immunological methods used mainly for rapid virus detection. However, only a few of these assays had been reported. CT imaging is still an important auxiliary diagnosis tool for COVID-19 patients, especially for symptomatic patients in the early stage, whose viral load is low and different to be identified by NAT. These diagnostic techniques are all good in some way and applying a combination of them will greatly improve the accuracy of COVID-19 diagnostics.

Compared to previous infectious diseases, more advanced contact tracing technologies are being applied in the pandemic, such as big data and contact tracing smartphone apps (Maccari and Cagno, 2021) . These technologies greatly improve the speed by which the relevant government departments respond to the outbreaks, but they also bring a lot of controversies such as privacy and ethics (Scassa, 2021) .

Additional measures, such as isolation and lockdown, to limit the movement of people were also applied which caused a lot of economic and social hardship as well (World Trade Organization, 2020; Zhang et al., 2021b) . Nevertheless, the availability of assays for the widespread, rapid, and early detection of COVID-19 infections will reduce the social demands of contact tracing and prevent extensive and extended lockdowns, as well as reducing the risk of being infected by close contacts.

Early detection, early isolation, and early diagnostic of COVID-19 patients are vital for winning the fight against the pandemic. Like all virological diagnostics, nucleic acid tests (NAT) and immunological assays are the most widely used methods for SARS-CoV-2 detection and the diagnosis of COVID-19 patients and asymptomatic carriers Eftekhari et al., 2021) . CT imaging is still important for COVID-19 diagnosis, especially for symptomatic patients in the early stage, whose viral load is low and different to be identified by NAT (De et al., 2021; Brogna et al., 2021) . The 8 th guideline for diagnosis and treatment of COVID-19 released by the National Health Commission (NHC) of China still added CT imaging in the diagnostic criteria to avoid false-negative results (National Health Commission of the People's Republic of China, 2020). Over the past 18 months, after the initial panic along with shortage of diagnosis and treatment resources, effective detection systems (reagents and equipment production, testing capacity expand, and skilled personnel training.) have been developed and applied in the spread control. Besides, research and development of new assays are emerging with understanding viral pathogenesis. Therefore, this mini-review focused on the developed diagnostic assays of COVID-19. We hoped it would provide more thoughts for developing novel diagnostic assays.

J o u r n a l P r e -p r o o f

With the development of sequencing technology, the whole genome sequence of SARS-CoV-2 was rapidly obtained and published on NCBI website on January 5, 2020 (GenBank: MN908947.3, . The SARS-CoV-2 genome consists of ORF1a and ORF1b (ORF1a and ORF1b coding 16 nonstructural proteins such as RNA-dependent RNA polymerase (Udugama et al., 2020) , S (spike protein), E (envelop protein), M (membrane protein), and N (nucleocapsid protein) (Touma, 2020) ( Figure 1 ). Based on the genome sequence of SARS-CoV-2, the specific target sequences are selected and used in NAT assays development. 

Real-time quantitative PCR (qPCR) is regarded as a gold standard for the detection of SARS-CoV-2 and is recommended by WHO and global CDCs. It is widely applied in departure and entry of people and goods, community screening for SARS-CoV-2 detection because of its rapidity and low cost. Chu et al. (2020) developed two one-step real-time reverse transcription PCR (rRT-PCR) methods to detect specific genes ORF1b and N, with the limit of detection (LOD) lower than 10 copies/reaction. Corman et al. (2020) reported the qPCR assay targeting E (envelope protein) gene and RdRp (RNA-dependent RNA polymerase) gene, and the LOD was 5.2 and 3.8 copies/reaction, respectively, while the sensitivity of N gene detection was slightly lower. Suo et al. (2020) reported a droplet digital PCR (ddPCR) assay has a limit significantly lower than RT-PCR ( Figure 2 ). Generally, it is recommended that COVID-19 patients can be identified only when two or more SARS-CoV-2 target gene sequences are detected as positive results. If only one target is positive, a retest J o u r n a l P r e -p r o o f is required. NAT with multiple target genes can effectively avoid false-positive results. Wuhan has tested 9,899,828 samples with this strategy in 16 days and the results were satisfactory. RNA extraction kits are the bottleneck of detection (Fomsgaard and Rosenstierne, 2020) , and the lack of RNA extraction kits affect the response to the pandemic. Fukumoto et al (2020) , Eckel et al (2020) , Hasan et al (2020) , and other researchers tried different methods to avoid the RNA extraction step. Unfortunately, the specificity and sensitivity of assays without the RNA extraction step were still inferior to those with the RNA extraction step. The false-negative rate of clinical samples was up to 83.0% compared with standard PCR assays (Eckel et al., 2020) .

This might be contributed to the lower sensitivity of detection without the RNA extraction step (Pearson et al., 2021 ). An additional heat step might help improve the sensitivity (Hasan et al, 2020) . Nevertheless, the virus RNA extraction and purification should be paid more attention to. Besides, there were also some studies tried other ways to increase detection efficiency such as comparing different samples treatment methods and thermocyclers (Ransom et al., 2020) , designing double-quencher probes (Hirotsu et al., 2020) , developing RT-PCR automated analyzer tool for SARS-CoV-2 detection (Dharavath et al., 2020) .

qPCR assay plays an important role in the clinical diagnosis of COVID-19 and there are numerous commercial products now (Iglói et al., 2020; Mostafa et al., 2020) .

In addition, various isothermal amplification assays such as loop-mediated isothermal amplification (LAMP) (Figure 3 (Table 1) . These isothermal amplification assays are more sensitive and independent of a thermal cycler, which makes them more suitable in rapid, high-throughput, and low-cost assays development. Among them, LAMP is the most mature isothermal amplification method and the LAMP assays for SARS-CoV-2 detection are the most used isothermal amplification method. 

Cas proteins including Cas 9, Cas 12, Cas 13, and Cas 14 can identify specific DNA/RNA sequences under a given condition and activate the activity of cleaving DNA or RNA fragments . This makes Cas proteins particularly suitable in the detection of nucleic acid sequences. The detection assays based on Cas proteins have been developed. However, Cas protein could not detect target DNA when its concentration is lower than 1 to 10 nM ). An isothermal amplification step was usually added before the detection of CRISPR-CasN-based assays. There have been several Cas-protein-based assays. Other novel assays such as DNA nano-scaffold based on SARS-CoV-2 RNA triggered isothermal amplification (The reaction time was about 10 min and the reaction temperature is between 15-35 °C) (Jiao et al., 2020) and visual "naked-eye" detection assay based on thiol-modified ASO-capped AuNPs (this assay has a detection limit of 0.18 ng/μL of RNA) (Moitra et al., 2020) has also been developed.

All these provide an alternative for SARS-CoV-2 detection.

It is noteworthy that the false-negative results of RT-PCR and other NAT assays appeared frequently (Woloshin et al., 2020) , which brings challenges to epidemic control. The reasons for false-negative results may be poor specificity of target genes or inadequate sensitivity of detection methods (Tahamtan and Ardebili, 2020) . The results showed that the detection methods currently applied in clinical practice need to strengthen the sensitivity to reduce false-negative results.

The sample collection methods also have an important impact on the accuracy of NAT results. Among them, nasopharyngeal swab sampling is the recommended method in most countries for detection of the nucleic acid of SARS-CoV-2 according to the characteristic of respiratory infectious disease. However, the nasopharyngeal J o u r n a l P r e -p r o o f swab sampling needs technical skills and puts the health care workers at risk of exposure. Saliva seems to be a good alternative. Saliva can be self-collected at a lower cost and few health care workers are needed. The virus RNA in saliva specimens is stable in 48 h (Matic et al., 2020) and SARS-CoV-2 in saliva can be detected even over one week (Williams et al., 2020) . Saliva shows good concordance with a nasopharyngeal swab (or even better than) for detection of SARS-CoV-2 in most recent reports Medeiros da Silva et al., 2020; Sakanashi et al., 2021; Sui et al., 2020) . Notably, the collection way of saliva will affect the detection result.

For example, hock-a-loogie saliva is better than saliva without cough Yee et al., 2020) . The U.S. Food and Drug Administration (FDA) had authorized the first in-home saliva collection for the detection of SARS-CoV-2 on May 08, 2020

(FDA, 2020). Besides, sputum is also another potential tool for detection .

Anyway, correct sampling operation and clinical application of new methods with high specificity and high sensitivity can reduce the risk of infection while sampling (Fabbris et al., 2021) , false-negative results, and improve the accuracy of NAT methods in COVID-19 diagnosis.

Immunological methods for COVID-19 diagnostics could be divided into two types: antibodies detection methods and antigens detection. For the former, we usually used serological tests to detect serum antibodies specific to SARS-CoV-2, which indicated if people were ever exposed to the virus or not. For the latter, we usually used prepared specific antibodies to develop detection methods, that was direct detection of the presence of SARS-CoV-2 antigens. They were valuable techniques for detecting COVID-19 patients with high viral load (that was super spreaders) at low cost (Pujadas et al., 2020) .

NAT assay usually indicates the current infection situation. Serological tests usually detect the antibody level in the serum, which indicates the situation of ever Some researchers believed that 30% to 60% of infection is asymptomatic (Qiu, 2020) . However, the asymptomatic carriers are also contagious, which may lead to a new outbreak. Nowadays, some countries and regions are in the late stage of the pandemic. Extensive serological tests can help to detect the previous infection, assess the progress of a regional epidemic situation, and predict the likely outcome of the epidemic.

The detection of serum antibodies is not suitable for rapid SARS-CoV-2 diagnostic. The developed rapid detection assays based on antibody tends to use a specific antibody to detect SARS-CoV-2 in samples directly or capture SARS-CoV-2 for further detection. Now, there have been some studies and commercial antigen detection kits for SARS-CoV-2 (Verma, Patel, and Pandya, 2020; Yuce, Filiztekin, and Ozkaya, 2021; Azzi et al., 2021) . Seo et al. (2020) immobilized antibody targeting SARS-CoV-2 spike protein on the graphene surface and prepared a field-effect transistor-based biosensor. This biosensor could detect SARS-CoV-2 with a concentration of 2.42 × 10 2 copies/mL in clinical samples. Karakuş et al. (2021) J o u r n a l P r e -p r o o f developed a colorimetric and electrochemical biosensor for SARS-CoV-2. The detection limit of it was 48 ng/mL SARS-CoV-2 spike antigen. Wang et al. (2021) developed a fluorescent immunochromatographic assay for SARS-CoV-2 based on multilayer quantum dot nanobead with a detection limit of 5 pg/mL SARS-CoV-2 NP antigen.

To avoid the long preparation period, Kim et al. (2020) used phage display technology to obtain single-chain variable fragment-crystallizable fragment (scFv-Fc) fusion antibodies specific to SARS-CoV-2 and developed a lateral flow immunoassay (LFIA)-based biosensor ( Figure 5 ). The reports of antigen detection kits were less than other detection methods although they were low cost and easy to use. This may be contributed to the long preparation period of specific antibodies and their sensitivity was generally lower than NAT methods (Liu and Rusling, 2021; Mak et al., 2020; Porte et al., 2020; Scohy et al., 2020) . immunoassay. It was interesting that the SARS-CoV S1 and MERS-CoV S1 proteins could not cause false-positive results although ACE2 was also the receptor of SARS-CoV and MERS-CoV.

These antigen detection assays based on specific antibodies or other macromolecules that can bind with SARS-CoV-2 are rapid and low-cost detection assays although the detection sensitivity is lower than NAT (Table 2 ). They may be suitable tools for rapid detection of COVID-19 to stop the spread. More attention should be paid to antigen detection. (Wang et al., 2021) Gold nanoparticle-based biosensor Spike antigen 48 ng/mL (Karakuş et al., 2021) Field-effect transistor-based biosensor Spike protein 2.42 copies/mL (Seo et al., 2020) ScFv-Fc biosensor NP antigen 2.5 × 10 4 pfu/reaction Aptamer NP antigen 10 ng/mL 

For the serological tests, all the detection assays are based on the detection of the antibodies specific to SARS-CoV-2 that are produced by the human immune system. The increase of the titer of the antibodies specific to SARS-CoV-2 is later than the infection (window period), so serological tests are not suitable for early diagnosis of COVID-19 (Wang, 2020f; Ma et al., 2020) . Serological tests are more suitable in the epidemiological survey and help to improve the accuracy of COVID-19 J o u r n a l P r e -p r o o f diagnosis. For example, the combination of serological and RT-PCR test has better sensitivity and specificity (Wang, 2020f) . Another important limitation of serological tests is the cross-reaction. The IgM and IgG specific to other viruses might also have the ability of binding SARS-CoV-2. For example, Zhu et al. (2020b) found the serum antibodies from SARS patients and immunized animals had a cross-reaction with SARS-CoV-2. This might bring a false positive result during traceability research.

Researchers had noticed this and try to avoid it (La Rosa et al., 2021) . For the same reason, the cross-reaction and long-period preparation of antibodies are also the limitations of antigen detection. This should be an important reason why there are only a few antigen detection assays.

Computed tomography imaging (CT imaging) is a kind of non-invasive medical imaging technique for diagnostics based on radiology. COVID-19 patients often have pulmonary inflammation. Chest CT examination can observe the imaging features of COVID-19 patients with multiple ground-glass opacity (GGO) in both lungs, which have the advantages of short time-consuming and high resolution (Wang et al., 2020e) .

Thus, CT imaging also became an important tool for the diagnosis of COVID-19.

The guideline for diagnosis and treatment of COVID-19 released by China NHC has included CT imaging in the diagnostic criteria to improve the accuracy of COVID-19 diagnosis. CT imaging can assist in the diagnosis of COVID-19. It was an important technique for the early detection of COVID-19 patients . (Mahmoud et al., 2020) .

Researchers also developed tools based on deep learning to provides automated detection and quantification of pneumonia by automated CT imaging analysis (Nayak et al., 2021; Zhang et al., 2020b) . This tool greatly reduces the workload although it cannot replace the role of the doctor now.

Although CT imaging is an important tool for the diagnosis of COVID-19, there are some limitations of its application. Hope et al. proposed that the imaging features of pneumonia in COVID-19 patients were not specific to the disease. It might appear in a series of infectious and non-communicable diseases. Positive chest CT results were only credible when COVID-19 was highly suspected (Hope, Raptis, and Henry, 2020) . The results of a chest CT examination for a definite diagnosis of COVID-19

should combine with NAT and immunological methods. In addition, the environmental safety of CT examinations should be considered. Given that COVID-19 is a highly contagious disease that can be spread through the air, the staff must take strict protective measures and the CT room should be thoroughly disinfected (Escudero et al., 2020; Kenarkoohi et al., 2020) .

With the acceleration of globalization, emerging infectious diseases are likely to Serological testing (namely detection of serum antibody specific to SARS-CoV-2), belongs to immunological methods, and also used in the diagnosis of COVID-19. However, the positive results of serological testing indicate the situation of infection at an undetermined time in the past, rather than the present situation.

Compared with serological testing, there are fewer reports about the SARS-CoV-2 antigen detection based on the specific antibody. To improve the accuracy, a combination of NAT and serological testing is recommended. Besides, CT imaging is also another important auxiliary diagnosis tool for improving the diagnostic accuracy of COVID-19.

In total, Researchers are still working on better detection assay development to further improve the sensitivity and detection speed, increase throughput and reduce cost. They will make a great contribution to terminate the epidemic.

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Correlation of chest CT and RT-PCR testing in coronavirus disease 2019 (COVID-19) in China: A report of 1014 cases

SARS-CoV2 testing: The limit of detection matters. bioRxiv: the preprint server for biology

Diagnostic Salivary Tests for SARS-CoV-2

Large-scale implementation of pooled RNA extraction and RT-PCR for SARS-CoV-2 detection

Sars-cov-2 detection in fecal sample from a patient with typical findings of covid-19 pneumonia on CT but negative to multiple sars-cov-2 rt-pcr tests on oropharyngeal and nasopharyngeal swab samples

Lifting of COVID-19 restrictions in the UK and the Delta variant

Multiplexed detection and quantification of human antibody response to COVID-19 infection using a plasmon enhanced biosensor platform

Improved molecular diagnosis of COVID-19 by the novel, highly sensitive and specific COVID-19-RdRp/Hel real-time reverse transcription-pcr assay validated in vitro and with clinical specimens

Pathogenicity and transmissibility of 2019-nCoV-A quick overview and comparison with other emerging viruses

A DNA aptamer-based method for detection of SARS-CoV-2 nucleocapsid protein

Molecular diagnosis of a novel coronavirus (2019-nCoV) causing an outbreak of pneumonia

Detection of 2019 novel coronavirus (2019-nCoV) by real-time RT-PCR

Diagnostic Performance of Chest CT for SARS-CoV-2 infection in individuals with or without COVID-19 Symptoms

An ultra-portable, self-contained point-of-care nucleic acid amplification test for diagnosis of active COVID-19 infection

Origin and evolution of pathogenic coronaviruses

A one-step, one-tube real-time RT-PCR based assay with an automated analysis for detection of SARS-CoV-2. Heliyon. 6, e04405

All-in-One Dual CRISPR-Cas12a (AIOD-CRISPR) Assay: A Case for Rapid, Ultrasensitive and visual detection of novel coronavirus SARS-CoV-2 and HIV virus. bioRxiv: the preprint server for biology

Rapid and sensitive detection of SARS-CoV-2 antibodies by biolayer interferometry

Variplex (TM) test system fails to reliably detect SARS-CoV-2 directly from respiratory samples without RNA extraction

A comprehensive review of detection methods for SARS-CoV-2. Microorganisms

SARS-CoV-2 analysis on environmental surfaces collected in an intensive care unit: keeping Ernest Shackleton's spirit

Is oro/nasopharyngeal swab for SARS-CoV-2 detection a safe procedure? Complications observed among a case series of 4876 consecutive swabs

Hock-a-loogie saliva as a diagnostic specimen for SARS-CoV-2 by a PCR-based assay: A diagnostic validity study

Sensitivity of chest CT for COVID-19: comparison to RT-PCR

An alternative workflow for molecular detection of SARS-CoV-2-escape from the NA extraction kit-shortage

Amplification-free detection of SARS-CoV-2 with CRISPR-Cas13a and mobile phone microscopy

Efficacy of a novel SARS-CoV-2 detection kit without RNA extraction and purification

Recent advances in detection technologies for COVID-19

The unsynchronized changes of CT image and nucleic acid detection in COVID-19: reports the two cases from Gansu, China

The species Severe acute respiratory syndrome-related coronavirus: classifying 2019-nCoV and naming it SARS-CoV-2

High-Throughput Transcription-mediated amplification on the Hologic Panther is a highly sensitive method of detection for SARS-CoV-2

SARS-CoV-2 detection with CRISPR diagnostics

Detection of SARS-CoV-2 RNA by direct RT-qPCR on nasopharyngeal specimens without extraction of viral RNA

Double-quencher probes improve detection sensitivity toward Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in a reverse-transcription polymerase chain reaction (RT-PCR) assay

Chest computed tomography for detection of coronavirus disease 2019 (COVID-19): don't rush the science

Clinical features of patients infected with 2019 novel coronavirus in Wuhan

Comparison of commercial realtime reverse transcription PCR assays for the detection of SARS-CoV-2

Covert coronavirus infections could be seeding new outbreaks

DNA nanoscaffold-based SARS-CoV-2 detection for COVID-19 diagnosis

Detection of the SARS-CoV-2 humanized antibody with paper-based ELISA

Colorimetric and electrochemical detection of SARS-CoV-2 spike antigen with a gold nanoparticle-based biosensor

Hospital indoor air quality monitoring for the detection of SARS-CoV-2 (COVID-19) virus

Isothermal SARS-CoV-2 Diagnostics: Tools for enabling distributed pandemic testing as a means of supporting safe reopenings

Development of a SARS-CoV-2-specific biosensor for antigen detection using scFv-Fc fusion proteins

SARS-CoV-2 has been circulating in northern Italy since December 2019: Evidence from environmental monitoring

A novel rapid detection for SARS-CoV-2 spike 1 antigens using human angiotensin converting enzyme 2 (ACE2)

Development and clinical application of a rapid IgM-IgG combined antibody test for SARS-CoV-2 infection diagnosis

Comparison of throat swabs and sputum specimens for viral nucleic acid detection in 52 cases of novel coronavirus (SARS-Cov-2)-infected pneumonia (COVID-19)

COVID-19 antibody tests and their limitations

Positive rate of RT-PCR detection of SARS-CoV-2 infection in 4880 cases from one hospital in

CT imaging analysis of 33 cases with the 2019 novel coronavirus infection

Coronaviruses and SARS-CoV-2: A Brief Overview

Development and comparison of novel multiple cross displacement amplification (MCDA) assays with other nucleic acid amplification methods for SARS-CoV-2 detection

Serum IgA, IgM, and IgG responses in COVID-19

Do we need a contact tracing app?

Can chest CT improve sensitivity of COVID-19 diagnosis in comparison to PCR? A meta-analysis study

Evaluation of rapid antigen test for detection of SARS-CoV-2 virus

Practical challenges to the clinical implementation of saliva for SARS-CoV-2 detection

Saliva as a possible tool for the SARS-CoV-2 detection: A review

Selective naked-eye Detection of SARS-CoV-2 mediated by n gene targeted antisense oligonucleotide capped plasmonic nanoparticles

Comparison of the analytical sensitivity of seven commonly used commercial SARS-CoV-2 automated molecular assays

Application of deep learning techniques for detection of COVID-19 cases using chest X-ray images: A comprehensive study

Development of diagnostic tests for detection of SARS-CoV-2

Comparing SARS-CoV-2 with SARS-CoV and influenza pandemics

Comparison of SARS-CoV-2 indirect and direct RT-qPCR detection methods

SARS-CoV-2 viral load predicts COVID-19 mortality

Covert coronavirus infections could be seeding new outbreaks

Comparison of extraction methods and thermocyclers for SARS-CoV-2 molecular detection using clinical specimens

Rapid detection of SARS-CoV-2 antibodies using electrochemical impedance-based detector

Dual lateral flow optical/chemiluminescence immunosensors for the rapid detection of salivary and serum IgA in patients with COVID-19 disease

Comparative evaluation of nasopharyngeal swab and saliva specimens for the molecular detection of SARS-CoV-2 RNA in Japanese patients with COVID-19

COVID-19 Contact tracing: From local to global and back again

Low performance of rapid antigen detection test as frontline testing for COVID-19 diagnosis

Rapid detection of COVID-19 causative virus (SARS-CoV-2) in Human nasopharyngeal swab specimens using field-effect transistor-based biosensor

Evaluation of saliva as an alternative diagnostic specimen source for SARS-CoV-2 detection by RT-dPCR

ddPCR: a more accurate tool for SARS-CoV-2 detection in low viral load specimens

Real-time RT-PCR in COVID-19 detection: issues affecting the results

COVID-19: molecular diagnostics overview

Immunological detection of serum antibodies in pediatric medical workers exposed to varying levels of SARS-CoV-2

Diagnosing COVID-19: the disease and tools for detection

Emerging diagnostic tools for detection of COVID-19 and perspective

Development of an ultrasensitive fluorescent immunochromatographic assay based on multilayer quantum dot nanobead for simultaneous detection of SARS-CoV-2 antigen and influenza A virus

A novel coronavirus outbreak of global health concern

The establishment of reference sequence for SARS-CoV-2 and variation analysis

Clinical characteristics of 138 hospitalized patients with 2019 novel coronavirus-infected pneumonia in Wuhan

Multiple-centre clinical evaluation of an ultrafast single-tube assay for SARS-CoV-2 RNA

Imaging manifestations and diagnostic value of chest CT of coronavirus disease 2019 (COVID-19) in the Xiaogan area

Combination of serological total antibody and RT-PCR test for detection of SARS-COV-2 infections

CRISPR/cas systems redefine nucleic acid detection: Principles and methods

Coronavirus pathogenesis and the emerging pathogen severe acute respiratory syndrome coronavirus. Microbiol

WHO, 2020. Novel Coronavirus(2019-nCoV) Situation Report -22

Detection of SARS-CoV-2 in saliva: implications for specimen transport and storage

False negative tests for SARS-CoV-2 infection -challenges and implications

Characteristics of and important lessons from the coronavirus disease 2019 (COVID-19) outbreak in China: summary of a report of 72314 cases from the Chinese Center for Disease Control and Prevention

A new coronavirus associated with human respiratory disease in China

Single-copy sensitive, field-deployable, and simultaneous dual-gene detection of SARS-CoV-2 RNA via modified RT-RPA

Antibody detection and dynamic characteristics in patients with COVID-19

Clinical course and outcomes of critically ill patients with SARS-CoV-2 pneumonia in Wuhan, China: a single-centered, retrospective, observational study

Saliva is a promising alternative specimen for the detection of SARS-CoV-2 in children and adults

Nucleic acid testing of sars-cov-2

Nucleic acid-based diagnostic tests for the detection SARS-CoV-2: An update

COVID-19 diagnosis -A review of current methods

Guangdong Provincial Institute of Public Health

The impact of relaxing interventions on human contact patterns and SARS-CoV-2 transmission in China

Automated detection and quantification of COVID-19 pneumonia: CT imaging analysis by a deep learning-based software

A protocol for detection of COVID-19 using CRISPR diagnostics

Analysis of the application value of serum antibody detection for staging of COVID-19 infection

A Novel Coronavirus from Patients with Pneumonia in China

Cross-reactive neutralization of SARS-CoV-2 by serum antibodies from recovered SARS patients and immunized animals

Rapid point-of-care testing for SARS-CoV-2 virus nucleic acid detection by an isothermal and nonenzymatic Signal amplification system coupled with a lateral flow immunoassay strip

Web references Tedros. WHO Director-General's opening remarks at the 8th meeting of the IHR Emergency Committee on COVID-19 -14

World merchandise trade fell 14% in volume, 21% in value in Q2

COVID-19) Update: FDA Authorizes First Diagnostic Test Using At-Home Collection of Saliva Specimens