Simpler and faster Covid-19 testing: Strategies to streamline SARS-CoV-2 molecular assays

Soft interface confined DNA walker for sensitive and specific detection of SARS-CoV-2 variants

Nucleic acid detection is conducive to preventing the spread of COVID-19 pandemic. In this work, we successfully designed a soft interface confined DNA walker by anchoring hairpin reporter probes on cell membranes for the detection of SARS-CoV-2 variants. In the presence of target RNA, the cyclic self-assembly reaction occurred between hairpin probes H1 and H2, and the continuous walking of target RNA on cell membranes led to the gradual amplification of fluorescence signal. The enrichment of H1 on membranes and the unique fluidity of membranes promoted the collision efficiency between DNA strands in the reaction process, endowing this method with high sensitivity. In addition, the double-blind test of synthetic RNA in 5% normal human serum demonstrated the good stability and anti-interference in complex environment of this method, which exhibited great potential in clinical diagnostics.

Economic Evaluation of COVID-19 Screening Tests and Surveillance Strategies in Low-Income, Middle-Income, and High-Income Countries: A Systematic Review

BACKGROUND Economic evaluation of the testing strategies to control transmission and monitor the severity of COVID-19 after the pandemic is essential. This study aimed to review the economic evaluation of COVID-19 tests and to construct a model with outcomes in terms of cost and test acceptability for surveillance in the post-pandemic period in low-income, middle-income, and high-income countries. MATERIAL AND METHODS We performed the systematic review following PRISMA guidelines through MEDLINE and EMBASE databases. We included the relevant studies that reported the economic evaluation of COVID-19 tests for surveillance. Also, we input current probability, sensitivity, and specificity for COVID-19 surveillance in the post-pandemic period. RESULTS A total of 104 articles met the eligibility criteria, and 8 articles were reviewed and assessed for quality. The specificity and sensitivity of COVID-19 screening tests were reported as 80% to 90% and 40% to 90%, respectively. The target population presented a mortality rate between 0.2% and 19.2% in the post-pandemic period. The implementation model of COVID-19 screening tests for surveillance with a cost mean for molecular and antigen tests was US$ 46.64 (min-max US $0.25-$105.39) and US $6.15 (min-max US $2-$10), respectively. CONCLUSIONS For the allocation budget for the COVID-19 surveillance test, it is essential to consider the incidence and mortality of the post-pandemic period in low-income, middle-income, and high-income countries. A robust method to evaluate outcomes is needed to prevent increasing COVID-19 incidents earlier.

Sensitive Pathogen Detection and Drug Resistance Characterization Using Pathogen-Derived Enzyme Activity Amplified by LAMP or CRISPR-Cas

Pathogens encapsulate or encode their own suite of enzymes to facilitate replication in the host. The pathogen-derived enzymes possess specialized activities that are essential for pathogen replication and have naturally been candidates for drug targets. Phenotypic assays detecting the activities of pathogen-derived enzymes and characterizing their inhibition under drugs offer an opportunity for pathogen detection, drug resistance testing for individual patients, and as a research tool for new drug development. Here, we used HIV as an example to develop assays targeting the reverse transcriptase (RT) enzyme encapsulated in HIV for sensitive detection and phenotypic characterization, with the potential for point-of-care (POC) applications. Specifically, we targeted the complementary (cDNA) generation activity of the HIV RT enzyme by adding engineered RNA as substrates for HIV RT enzyme to generate cDNA products, followed by cDNA amplification and detection facilitated by loop-mediated isothermal amplification (LAMP) or CRISPR-Cas systems. To guide the assay design, we first used qPCR to characterize the cDNA generation activity of HIV RT enzyme. In the LAMP-mediated Product-Amplified RT activity assay (LamPART), the cDNA generation and LAMP amplification were combined into one pot with novel assay designs. When coupled with direct immunocapture of HIV RT enzyme for sample preparation and endpoint lateral flow assays for detection, LamPART detected as few as 20 copies of HIV RT enzyme spiked into 25μL plasma (fingerstick volume), equivalent to a single virion. In the Cas-mediated Product-Amplified RT activity assay (CasPART), we tailored the substrate design to achieve a LoD of 2e4 copies (1.67fM) of HIV RT enzyme. Furthermore, with its phenotypic characterization capability, CasPART was used to characterize the inhibition of HIV RT enzyme under antiretroviral drugs and differentiate between wild-type and mutant HIV RT enzyme for potential phenotypic drug resistance testing. Moreover, the CasPART assay can be readily adapted to target the activity of other pathogen-derived enzymes. As a proof-of-concept, we successfully adapted CasPART to detect HIV integrase with a sensitivity of 83nM. We anticipate the developed approach of detecting enzyme activity with product amplification has the potential for a wide range of pathogen detection and phenotypic characterization.

Optimization of extraction-free protocols for SARS-CoV-2 detection using a commercial rRT-PCR assay

In the ongoing global fight against coronavirus disease 2019 (COVID-19), the sample preparation process for real-time reverse transcription polymerase chain reaction (rRT-PCR) faces challenges due to time-consuming steps, labor-intensive procedures, contamination risks, resource demands, and environmental implications. However, optimized strategies for sample preparation have been poorly investigated, and the combination of RNase inhibitors and Proteinase K has been rarely considered. Hence, we investigated combinations of several extraction-free protocols incorporating heat treatment, sample dilution, and Proteinase K and RNase inhibitors, and validated the effectiveness using 120 SARS-CoV-2 positive and 62 negative clinical samples. Combining sample dilution and heat treatment with Proteinase K and RNase inhibitors addition exhibited the highest sensitivity (84.26%) with a mean increase in cycle threshold (Ct) value of + 3.8. Meanwhile, combined sample dilution and heat treatment exhibited a sensitivity of 79.63%, accounting for a 38% increase compared to heat treatment alone. Our findings highlight that the incorporation of Proteinase K and RNase inhibitors with sample dilution and heat treatment contributed only marginally to the improvement without yielding statistically significant differences. Sample dilution significantly impacts SARS-CoV-2 detection, and sample conditions play a crucial role in the efficiency of extraction-free methods. Our findings may provide insights for streamlining diagnostic testing, enhancing its accessibility, cost-effectiveness, and sustainability.

Rapid, high-sensitivity detection of biomolecules using dual-comb biosensing

Rapid, sensitive detection of biomolecules is important for biosensing of infectious pathogens as well as biomarkers and pollutants. For example, biosensing of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is still strongly required for the fight against coronavirus disease 2019 (COVID-19) pandemic. Here, we aim to achieve the rapid and sensitive detection of SARS-CoV-2 nucleocapsid protein antigen by enhancing the performance of optical biosensing based on optical frequency combs (OFC). The virus-concentration-dependent optical spectrum shift produced by antigen-antibody interactions is transformed into a photonic radio-frequency (RF) shift by a frequency conversion between the optical and RF regions in the OFC, facilitating rapid and sensitive detection with well-established electrical frequency measurements. Furthermore, active-dummy temperature-drift compensation with a dual-comb configuration enables the very small change in the virus-concentration-dependent signal to be extracted from the large, variable background signal caused by temperature disturbance. The achieved performance of dual-comb biosensing will greatly enhance the applicability of biosensors to viruses, biomarkers, environmental hormones, and so on.

A novel paper-based lysis strip for SARS-CoV-2 RNA detection at low resource settings

Infectious respiratory diseases such as COVID-19 are serious and global concerns from the past to the present. To isolate the spread of infectious diseases even in the absence of a health system, a simple, inexpensive, reliable, sensitive, and selective molecular diagnosis platform for Point of Care Test (POCT) is required. Especially, the nucleic acid extraction step is difficult to perform out of laboratory. Here, we propose a paper-based lysis (PBL) strip for nucleic acid extraction, especially in low-resource settings (LRS). PBL strips are suitable for isolating RNA from viruses with biological interference and inhibitors. We optimized the buffer compositions and membranes of the strip. A simple preparation method using a PBL strip could obtain an eluent for downstream inspection within 20 min. Overall, 10⁴ copies/swaps were detected for 20 min for amplification in combination with Reverse Transcription Loop-Mediated Amplification (RT-LAMP).

SMART: A Swing-Assisted Multiplexed Analyzer for Point-of-Care Respiratory Tract Infection Testing

Respiratory tract infections such as the ongoing coronavirus disease 2019 (COVID-19) has seriously threatened public health in the last decades. The experience of fighting against the epidemic highlights the importance of user-friendly and accessible point-of-care systems for nucleic acid (NA) detection. To realize low-cost and multiplexed point-of-care NA detection, a swing-assisted multiplexed analyzer for point-of-care respiratory tract infection testing (SMART) was proposed to detect multiple respiratory tract pathogens using visible loop-mediated isothermal amplification. By performing hand-swing movements to generate acceleration force to distribute samples into reaction chambers, the design of the SMART system was greatly simplified. By using different format of chips and integrating into a suitcase, this system can be applied to on-site multitarget and multi-sample testing. Three targets including the N and Orf genes of SARS-CoV-2 and the internal control were simultaneously analyzed (limit of detection: 2000 copies/mL for raw sample; 200 copies/mL for extracted sample). Twenty-three clinical samples with eight types of respiratory bacteria and twelve COVID-19 clinical samples were successfully detected. These results indicate that the SMART system has the potential to be further developed as a versatile tool in the diagnosis of respiratory tract infection.

Electrochemical immunosensor nanoarchitectonics with the Ag-rGO nanocomposites for the detection of receptor-binding domain of SARS-CoV-2 spike protein

As the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) poses a grave threat to human life and health, it is essential to develop an efficient and sensitive detection method to identify infected individuals. This study described an electrode platform immunosensor to detect SARS-CoV-2-specific spike receptor-binding domain (RBD) protein based on a bare gold electrode modified with Ag-rGO nanocomposites and the biotin-streptavidin interaction system. The Ag-rGO nanocomposites was obtained by chemical synthesis and characterized by electrochemistry and scanning electron microscope (SEM). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to record the electrochemical signals in the electrode modification. The differential pulse voltammetry (DPV) results showed that the limit of detection (LOD) of the immunosensor was 7.2 fg mL^-1 and the linear dynamic detection range was 0.015 ~ 158.5 pg mL^-1. Furthermore, this sensitive immunosensor accurately detected RBD in artificial saliva with favorable stability, specificity, and reproducibility, indicating that it has the potential to be used as a practical method for the detection of SARS-CoV-2.

Multiplex Target-Redundant RT-LAMP for Robust Detection of SARS-CoV-2 Using Fluorescent Universal Displacement Probes

The increasing prevalence of variant lineages during the COVID-19 pandemic has the potential to disrupt molecular diagnostics due to mismatches between primers and variant templates. Point-of-care molecular diagnostics, which often lack the complete functionality of their high-throughput laboratory counterparts, are particularly susceptible to this type of disruption, which can result in false-negative results. To address this challenge, we have developed a robust Loop Mediated Isothermal Amplification assay with single tube multiplexed multitarget redundancy and an internal amplification control. A convenient and cost-effective target-specific fluorescence detection system allows amplifications to be grouped by signal using adaptable probes for pooled reporting of SARS-CoV-2 target amplifications or differentiation of the Internal Amplification Control. Over the course of the pandemic, primer coverage of viral lineages by the three redundant sub-assays has varied from assay to assay as they have diverged from the Wuhan-Hu-1 isolate sequence, but aggregate coverage has remained high for all variant sequences analyzed, with a minimum of 97.4% (Variant of Interest: Eta). In three instances (Delta, Gamma, Eta), a high-frequency mismatch with one of the three sub-assays was observed, but overall coverage remained high due to multitarget redundancy. When challenged with extracted human samples the multiplex assay showed 87% or better sensitivity (of 30 positive samples), with 100% sensitivity for samples containing greater than 30 copies of viral RNA per reaction (of 21 positive samples), and 100% specificity (of 60 negative samples). These results are further evidence that conventional laboratory methodologies can be leveraged at the point of care for robust performance and diagnostic stability over time. IMPORTANCE The COVID-19 pandemic has had tremendous impact, and the ability to perform molecular diagnostics in resource limited settings has emerged as a key resource for mitigating spread of the disease. One challenge in COVID-19 diagnosis, as well as other viruses, is ongoing mutation that can allow viruses to evade detection by diagnostic tests. We developed a test that detects multiple parts of the virus genome in a single test to reduce the chance of missing a virus due to mutation, and it is designed to be simpler and faster than typical laboratory tests while maintaining high sensitivity. This capability is enabled by a novel fluorescent probe technology that works with a simple constant temperature reaction condition.

Evaluation and Clinical Validation of Guanidine-Based Inactivation Transport Medium for Preservation of SARS-CoV-2

WHO declared the outbreak of COVID-19, caused by SARS-CoV-2, a pandemic in March 2020. More than 223 million cases and approximately 4.6 million deaths have been confirmed. Early diagnosis and immediate treatment became a priority during this pandemic. However, COVID-19 diagnostic testing resources are limited, especially early in the pandemic. Apart from being limited, the COVID-19 diagnostic tests using reverse transcription polymerase chain reaction (RT-PCR) have encountered storage, transportation, and safety issues. These problems are mainly experienced by developing poor countries, countries in the equatorial region, and archipelagic countries. VITPAD® is a guanidine-based inactivation transport medium (ITM) formulated to maintain the RNA quality of SARS-CoV-2 during transportation without cold chains. This study, conducted from September 2020 to March 2021, performed clinical validation of VITPAD® by comparing its performance with a globally commercially available ITM from the NEST brand. Its stability at room temperature, safety, and resistance at high temperatures was also tested using RT-PCR analysis. VITPAD® can reduce the infectious nature of the specimen, preserve the SARS-CoV-2 for 18 days at an ambient temperature, and resist high temperatures (40°C for 3 hours). A guanidine-based transport medium, such as VITPAD®, is compatible and recommended for RT-PCR-based molecular diagnosis of COVID-19.

Passively sensing SARS-CoV-2 RNA in public transit buses

Affordably tracking the transmission of respiratory infectious diseases in urban transport infrastructures can inform individuals about potential exposure to diseases and guide public policymakers to prepare timely responses based on geographical transmission in different areas in the city. Towards that end, we designed and tested a method to detect SARS-CoV-2 RNA in the air filters of public buses, revealing that air filters could be used as passive fabric sensors for the detection of viral presence. We placed and retrieved filters in the existing HVAC systems of public buses to test for the presence of trapped SARS-CoV-2 RNA using phenol-chloroform extraction and RT-qPCR. SARS-CoV-2 RNA was detected in 14% (5/37) of public bus filters tested in Seattle, Washington, from August 2020 to March 2021. These results indicate that this sensing system is feasible and that, if scaled, this method could provide a unique lens into the geographically relevant transmission of SARS-CoV-2 through public transit rider vectors, pooling samples of riders over time in a passive manner without installing any additional systems on transit vehicles.

SARS-CoV-2 Diagnostics Based on Nucleic Acids Amplification: From Fundamental Concepts to Applications and Beyond

COVID-19 pandemic ignited the development of countless molecular methods for the diagnosis of SARS-CoV-2 based either on nucleic acid, or protein analysis, with the first establishing as the most used for routine diagnosis. The methods trusted for day to day analysis of nucleic acids rely on amplification, in order to enable specific SARS-CoV-2 RNA detection. This review aims to compile the state-of-the-art in the field of nucleic acid amplification tests (NAATs) used for SARS-CoV-2 detection, either at the clinic level, or at the Point-Of-Care (POC), thus focusing on isothermal and non-isothermal amplification-based diagnostics, while looking carefully at the concerning virology aspects, steps and instruments a test can involve. Following a theme contextualization in introduction, topics about fundamental knowledge on underlying virology aspects, collection and processing of clinical samples pave the way for a detailed assessment of the amplification and detection technologies. In order to address such themes, nucleic acid amplification methods, the different types of molecular reactions used for DNA detection, as well as the instruments requested for executing such routes of analysis are discussed in the subsequent sections. The benchmark of paradigmatic commercial tests further contributes toward discussion, building on technical aspects addressed in the previous sections and other additional information supplied in that part. The last lines are reserved for looking ahead to the future of NAATs and its importance in tackling this pandemic and other identical upcoming challenges.

Implementation of an interactive mobile application to pilot a rapid assay to detect HIV drug resistance mutations in Kenya

Usability is an overlooked aspect of implementing lab-based assays, particularly novel assays in low-resource-settings. Esoteric instructions can lead to irreproducible test results and patient harm. To address these issues, we developed a software application based on "Aquarium", a laboratory-operating system run on a computer tablet that provides step-by-step digital interactive instructions, protocol management, and sample tracking. Aquarium was paired with a near point-of-care HIV drug resistance test, "OLA-Simple", that detects mutations associated with virologic failure. In this observational study we evaluated the performance of Aquarium in guiding untrained users through the multi-step laboratory protocol with little supervision. To evaluate the training by Aquarium software we conducted a feasibility study in a laboratory at Coptic Hope Center in Nairobi, Kenya. Twelve volunteers who were unfamiliar with the kit performed the test on blinded samples (2 blood specimens; 5 codons/sample). Steps guided by Aquarium included: CD4+ T-Cell separation, PCR, ligation, detection, and interpretation of test results. Participants filled out a short survey regarding their demographics and experience with the software and kit. None of the laboratory technicians had prior experience performing CD4+ separation and 7/12 had no experience performing laboratory-based molecular assays. 12/12 isolated CD4+ T cells from whole blood with yields comparable to isolations performed by trained personnel. The OLA-Simple workflow was completed by all, with genotyping results interpreted correctly by unaided-eye in 108/120 (90%) and by software in 116/120 (97%) of codons analyzed. In the surveys, participants favorably assessed the use of software guidance. The Aquarium digital instructions enabled first-time users in Kenya to complete the OLA-simple kit workflow with minimal training. Aquarium could increase the accessibility of laboratory assays in low-resource-settings and potentially standardize implementation of clinical laboratory tests.

Implementation of an interactive mobile application to pilot a rapid assay to detect HIV drug resistance mutations in Kenya

Usability is an overlooked aspect of implementing lab-based assays, particularly novel assays in low-resource-settings. Esoteric instructions can lead to irreproducible test results and patient harm. To address these issues, we developed a software application based on "Aquarium", a laboratory-operating system run on a computer tablet that provides step-by-step digital interactive instructions, protocol management, and sample tracking. Aquarium was paired with a near point-of-care HIV drug resistance test, "OLA-Simple", that detects mutations associated with virologic failure. In this observational study we evaluated the performance of Aquarium in guiding untrained users through the multi-step laboratory protocol with little supervision. To evaluate the training by Aquarium software we conducted a feasibility study in a laboratory at Coptic Hope Center in Nairobi, Kenya. Twelve volunteers who were unfamiliar with the kit performed the test on blinded samples (2 blood specimens; 5 codons/sample). Steps guided by Aquarium included: CD4+ T-Cell separation, PCR, ligation, detection, and interpretation of test results. Participants filled out a short survey regarding their demographics and experience with the software and kit. None of the laboratory technicians had prior experience performing CD4+ separation and 7/12 had no experience performing laboratory-based molecular assays. 12/12 isolated CD4+ T cells from whole blood with yields comparable to isolations performed by trained personnel. The OLA-Simple workflow was completed by all, with genotyping results interpreted correctly by unaided-eye in 108/120 (90%) and by software in 116/120 (97%) of codons analyzed. In the surveys, participants favorably assessed the use of software guidance. The Aquarium digital instructions enabled first-time users in Kenya to complete the OLA-simple kit workflow with minimal training. Aquarium could increase the accessibility of laboratory assays in low-resource-settings and potentially standardize implementation of clinical laboratory tests.

Simultaneous monitoring of HIV viral load and screening of SARS-CoV-2 employing a low-cost RT-qPCR test workflow

This new workflow enables co-extraction of HIV and SARS-CoV2 RNAs from clinical pooled plasma/nasal secretion samples that allows sensitive detection of SARS-CoV-2 and HIV infections in the patients-living with HIV.

Isothermal Amplification with a Target-Mimicking Internal Control and Quantitative Lateral Flow Readout for Rapid HIV Viral Load Testing in Low-Resource Settings

Point-of-care diagnostics often use isothermal nucleic acid amplification for qualitative detection of pathogens in low-resource healthcare settings but lack sufficient precision for quantitative applications such as HIV viral load monitoring. Although viral load (VL) monitoring is an essential component of HIV treatment, commercially available tests rely on relatively high-resource chemistries like real-time polymerase chain reaction and are thus used on an infrequent basis for millions of people living with HIV in low-income countries. To address the constraints of low-resource settings on nucleic acid quantification, we describe a recombinase polymerase amplification and lateral flow detection approach that quantifies HIV-1 DNA or RNA by comparison to a competitive internal amplification control (IAC) of a known copy number, which may be set to any useful threshold (in our case, a clinically relevant threshold for HIV treatment failure). The IAC is designed to amplify alongside the HIV target with a similar efficiency, allowing for normalization of the assay to variation or inhibition and enabling an endpoint readout that is compatible with commercially available kits for nucleic acid lateral flow detection and interpretable with minimal instrumentation or by the naked eye. We find that this approach can reliably differentiate ≤600 or ≥1400 copies of HIV DNA from a 1000-copy threshold when lateral flow strips are imaged with a conventional office scanner and analyzed with free densitometry software. We further demonstrate a user-friendly adaptation of this analysis to process cell phone photographs with an automated script. Alternatively, we show via a survey that 21 minimally trained volunteers could reliably resolve ≥10-fold (log₁₀) differences of HIV DNA or RNA by naked eye interpretation of lateral flow results. This amplification and detection workflow requires minimal instrumentation, takes just 30 min to complete, and when combined with a suitable sample preparation method, may enable HIV VL testing while the patient waits or a self-test, which has the potential to improve care. This approach may be adapted for other applications that require quantitative analysis of a nucleic acid target in low-resource settings.

Harmony COVID-19: A ready-to-use kit, low-cost detector, and smartphone app for point-of-care SARS-CoV-2 RNA detection

RNA amplification tests sensitively detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, but their complexity and cost are prohibitive for expanding coronavirus disease 2019 (COVID-19) testing. We developed “Harmony COVID-19,” a point-of-care test using inexpensive consumables, ready-to-use reagents, and a simple device. Our ready-to-use, multiplexed reverse transcription, loop-mediated isothermal amplification (RT-LAMP) can detect down to 0.38 SARS-CoV-2 RNA copies/μl and can report in 17 min for high–viral load samples (5000 copies/μl). Harmony detected 97 or 83% of contrived samples with ≥0.5 viral particles/μl in nasal matrix or saliva, respectively. Evaluation in clinical nasal specimens (n = 101) showed 100% detection of RNA extracted from specimens with ≥0.5 SARS-CoV-2 RNA copies/μl, with 100% specificity in specimens positive for other respiratory pathogens. Extraction-free analysis (n = 29) had 95% success in specimens with ≥1 RNA copies/μl. Usability testing performed first time by health care workers showed 95% accuracy.

Rapid Near Point-of-Care Assay for HLA-B*57:01 Genotype Associated with Severe Hypersensitivity Reaction to Abacavir

The nucleoside reverse transcriptase inhibitor abacavir (ABC) is used commonly to treat young children with HIV infection and is a component of the fixed-dose-combination Triumeq^®. ABC can trigger a severe hypersensitivity reaction in people who are homozygous or heterozygous for HLA-B*57:01. Testing for HLA-B*57:01 before ABC initiation is standard-of-care in high-resource settings, but current tests are costly or difficult to access in resource-limited settings. To address these gaps, we developed an inexpensive simple-to-use rapid assay to detect HLA-B*57:01. We designed and optimized a multiplexed polymerase chain reaction (PCR) to amplify HLA-B*57 subtypes and the human beta-globin gene; employed probes and ligation to specifically tag the HLA-B*57:01 allele with biotin. Tagged-ligated products were detected by immunocapture in an enzyme-linked immunosorbent assay plate or lateral flow strip. Cell lines with known HLA genotypes were used to optimize the assay. The optimized assay was then compared with genotypes of clinical specimens (n = 60) determined by sequencing, with specimens enriched for individuals with HLA-B*57:01. The optimized assay utilizes 40-min 35-cycle multiplex PCR for B*57 and beta-globin; 20-min ligation reaction; and 15-min detection. Evaluation of the HLA-B*57:01 oligonucleotide ligation assay using clinical specimens had a sensitivity of 100% (n = 27/27 typed as B*57:01) and specificity of 100% (n = 33/33 typed as non-B*57:01) by visual interpretation of lateral flow strips. The cost is US$5.96/specimen. This rapid and economical assay accurately detects HLA-B*57:01 in clinical specimens. Use of this assay could expand access to HLA-B*57:01 genotyping and facilitate safe same-day initiation of ABC-based treatment.

Rapid and highly sensitive one-tube colorimetric RT-LAMP assay for visual detection of SARS-CoV-2 RNA

Coronavirus disease 2019 (COVID-19), caused by SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) is a highly contagious disease. To tame the continuously raging outbreak of COVID-19, developing a cheap, rapid and sensitive testing assay is absolutely imperative. Herein, we developed a one-tube colorimetric RT-LAMP assay for the visual detection of SARS-CoV-2 RNA. The assay integrates Si-OH magnetic beads (MBs)-based fast RNA extraction and rapid isothermal amplification in a single tube, thus bypassing the RNA elution step and directly amplifying on-beads RNA molecules with the visualized results. This one-tube assay has a limit of detection (LOD) as low as 200 copies/mL for sample input volumes of up to 600 μL, and can be performed in less than 1 h from sample collection to result readout. This assay demonstrated a 100% concordance with the gold standard test RT-qPCR test by using 29 clinical specimens and showed high specificity. This one-tube colorimetric RT-LAMP assay can serve as an alternative platform for a rapid and sensitive diagnostic test for COVID-19 and is particularly suitable for use at community clinics or township hospitals.

Inexpensive workflow for simultaneous monitoring of HIV viral load and detection of SARS-CoV-2 infection

BACKGROUND

COVID-19 pandemic interrupted routine care for individuals living with HIV, putting them at risk of becoming virologically unsuppressed and ill. Often they are at high risk for exposure to SARS-CoV-2 infection and severe disease once infected. For this population, it is urgent to closely monitor HIV plasma viral load ( VL ) and screen for SARS-COV-2 infection.

METHOD

We have developed a non-proprietary method to isolate RNA from plasma, nasal secretions ( NS ), or both. HIV, SARS-CoV-2, and human RP targets in extracted RNA are then RT-qPCR to estimate the VL and classify HIV/SARS-CoV-2 status ( i . e ., HIV as VL failure or suppressed; SARS-CoV-2 as positive, presumptive positive, negative, or indeterminate). We evaluated this workflow on 133 clinical specimens: 40 plasma specimens (30 HIV-seropositive), 67 NS specimens (31 SARS-CoV-2-positive), and 26 pooled plasma/NS specimens (26 HIV-positive with 10 SARS-CoV-2-positive), and compared the results obtained using the in-house extraction to those using a commercial extraction kit.

RESULTS

In-house extraction had a detection limit of 200-copies/mL for HIV and 100-copies/mL for SARS-CoV-2. In-house and commercial methods yielded positively correlated HIV VL (R ² : 0.98 for contrived samples; 0.81 for seropositive plasma). SARS-CoV-2 detection had 100% concordant classifications in contrived samples, and in clinical NS extracted by in-house method, excluding indeterminate results, was 95% concordant (25 positives, 6 presumptive positives, and 31 negatives) to those using the commercial method. Analysis of pooled plasma/NS showed R ² of 0.91 (contrived samples) and 0.71 (clinical specimens) for HIV VL correlations obtained by both extraction methods, while SARS-CoV-2 detection showed 100% concordance in contrived and clinical specimens.

INTERPRETATION

Our low-cost workflow for molecular testing of HIV and SARS-CoV-2 could serve as an alternative to current standard assays for laboratories in low-resource settings.

Multiplex Target-Redundant RT-LAMP for Robust Detection of SARS-CoV-2 Using Fluorescent Universal Displacement Probes

The increasing prevalence of variant lineages during the COVID-19 pandemic has the potential to disrupt molecular diagnostics due to mismatches between primers and variant templates. Point-of-care molecular diagnostics, which often lack the complete functionality of their high throughput laboratory counterparts, are particularly susceptible to this type of disruption, which can result in false negative results. To address this challenge, we have developed a robust Loop Mediated Isothermal Amplification assay with single tube multiplexed multi-target redundancy and an internal amplification control. A convenient and cost-effective target specific fluorescence detection system allows amplifications to be grouped by signal using adaptable probes for pooled reporting of SARS-COV-2 target amplifications or differentiation of the Internal Amplification Control. Over the course of the pandemic, primer coverage of viral lineages by the three redundant sub-assays has varied from assay to assay as they have diverged from the Wuhan-Hu-1 isolate sequence, but aggregate coverage has remained high for all variant sequences analyzed, with a minimum of 97.4% (Variant of Interest: Eta). In three instances (Delta, Gamma, Eta), a high frequency mismatch with one of the three sub-assays was observed, but overall coverage remained high due to multi-target redundancy. When challenged with extracted human samples the multiplexed assay showed 100% sensitivity for samples containing greater than 30 copies of viral RNA per reaction, and 100% specificity. These results are further evidence that conventional laboratory methodologies can be leveraged at the point-of-care for robust performance and diagnostic stability over time.

Rethinking COVID-19 test sensitivity-a strategy for improving the detection limit

Numerous genetic tests for the detection of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus, including those based on the ever-popular real-time polymerase chain reaction (RT-qPCR) technique, have been reported. These diagnostic tests give false negatives particularly during the early and late stages of COVID-19 clearly indicating inadequate test sensitivity. The entire COVID-19 diagnostic workflow is often overlooked and given very little attention. Herein, we propose that volumetric modifications to COVID-19 workflows would significantly improve detection limits. We would therefore encourage researchers to adopt a holistic approach, in which all the steps of a COVID-19 diagnostic workflow, are carefully scrutinised, particularly those upstream factors at the viral sampling and pre-analytical stages.