Analytical sensitivity of seven point-of-care influenza virus detection tests and two molecular tests for detection of avian origin H7N9 and swine origin H3N2 variant influenza A viruses

Nanoisland SERS-Substrates for Specific Detection and Quantification of Influenza A Virus

Surface-enhanced Raman spectroscopy (SERS)-based aptasensors for virus determination have attracted a lot of interest recently. This approach provides both specificity due to an aptamer component and a low limit of detection due to signal enhancement by a SERS substrate. The most successful SERS-based aptasensors have a limit of detection (LoD) of 10-100 viral particles per mL (VP/mL) that is advantageous compared to polymerase chain reactions. These characteristics of the sensors require the use of complex substrates. Previously, we described silver nanoisland SERS-substrate with a reproducible and uniform surface, demonstrating high potency for industrial production and a suboptimal LoD of 4 × 105 VP/mL of influenza A virus. Here we describe a study of the sensor morphology, revealing an unexpected mechanism of signal enhancement through the distortion of the nanoisland layer. A novel modification of the aptasensor was proposed with chromium-enhanced adhesion of silver nanoparticles to the surface as well as elimination of the buffer-dependent distortion-triggering steps. As a result, the LoD of the Influenza A virus was decreased to 190 VP/mL, placing the nanoisland SERS-based aptasensors in the rank of the most powerful sensors for viral detection.

Trends of respiratory virus detection in point-of-care testing: A review

In resource-limited conditions such as the COVID-19 pandemic, on-site detection of diseases using the Point-of-care testing (POCT) technique is becoming a key factor in overcoming crises and saving lives. For practical POCT in the field, affordable, sensitive, and rapid medical testing should be performed on simple and portable platforms, instead of laboratory facilities. In this review, we introduce recent approaches to the detection of respiratory virus targets, analysis trends, and prospects. Respiratory viruses occur everywhere and are one of the most common and widely spreading infectious diseases in the human global society. Seasonal influenza, avian influenza, coronavirus, and COVID-19 are examples of such diseases. On-site detection and POCT for respiratory viruses are state-of-the-art technologies in this field and are commercially valuable global healthcare topics. Cutting-edge POCT techniques have focused on the detection of respiratory viruses for early diagnosis, prevention, and monitoring to protect against the spread of COVID-19. In particular, we highlight the application of sensing techniques to each platform to reveal the challenges of the development stage. Recent POCT approaches have been summarized in terms of principle, sensitivity, analysis time, and convenience for field applications. Based on the analysis of current states, we also suggest the remaining challenges and prospects for the use of the POCT technique for respiratory virus detection to improve our protection ability and prevent the next pandemic.

Multiplex Lithographic SERS Aptasensor for Detection of Several Respiratory Viruses in One Pot

Rapid and reliable techniques for virus identification are required in light of recurring epidemics and pandemics throughout the world. Several techniques have been distributed for testing the flow of patients. Polymerase chain reaction with reverse transcription is a reliable and sensitive, though not rapid, tool. The antibody-based strip is a rapid, though not reliable, and sensitive tool. A set of alternative tools is being developed to meet all the needs of the customer. Surface-enhanced Raman spectroscopy (SERS) provides the possibility of single molecule detection taking several minutes. Here, a multiplex lithographic SERS aptasensor was developed aiming at the detection of several respiratory viruses in one pot within 17 min. The four labeled aptamers were anchored onto the metal surface of four SERS zones; the caught viruses affect the SERS signals of the labels, providing changes in the analytical signals. The sensor was able to decode mixes of SARS-CoV-2 (severe acute respiratory syndrome coronavirus two), influenza A virus, respiratory syncytial virus, and adenovirus within a single experiment through a one-stage recognition process.

Aptamer-coated track-etched membranes with a nanostructured silver layer for single virus detection in biological fluids

Aptasensors based on surface-enhanced Raman spectroscopy (SERS) are of high interest due to the superior specificity and low limit of detection. It is possible to produce stable and cheap SERS-active substrates and portable equipment meeting the requirements of point-of-care devices. Here we combine the membrane filtration and SERS-active substrate in the one pot. This approach allows efficient adsorption of the viruses from the solution onto aptamer-covered silver nanoparticles. Specific determination of the viruses was provided by the aptamer to influenza A virus labeled with the Raman-active label. The SERS-signal from the label was decreased with a descending concentration of the target virus. Even several virus particles in the sample provided an increase in SERS-spectra intensity, requiring only a few minutes for the interaction between the aptamer and the virus. The limit of detection of the aptasensor was as low as 10 viral particles per mL (VP/mL) of influenza A virus or 2 VP/mL per probe. This value overcomes the limit of detection of PCR techniques (∼10³ VP/mL). The proposed biosensor is very convenient for point-of-care applications.

Recent advances in immunoassay technologies for the detection of human coronavirus infections

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is the seventh coronavirus (CoV) that has spread in humans and has become a global pandemic since late 2019. Efficient and accurate laboratory diagnostic methods are one of the crucial means to control the development of the current pandemic and to prevent potential future outbreaks. Although real-time reverse transcription-polymerase chain reaction (rRT-PCR) is the preferred laboratory method recommended by the World Health Organization (WHO) for diagnosing and screening SARS-CoV-2 infection, the versatile immunoassays still play an important role for pandemic control. They can be used not only as supplemental tools to identify cases missed by rRT-PCR, but also for first-line screening tests in areas with limited medical resources. Moreover, they are also indispensable tools for retrospective epidemiological surveys and the evaluation of the effectiveness of vaccination. In this review, we summarize the mainstream immunoassay methods for human coronaviruses (HCoVs) and address their benefits, limitations, and applications. Then, technical strategies based on bioinformatics and advanced biosensors were proposed to improve the performance of these methods. Finally, future suggestions and possibilities that can lead to higher sensitivity and specificity are provided for further research.

Model of the SARS-CoV-2 Virus for Development of a DNA-Modified, Surface-Enhanced Raman Spectroscopy Sensor with a Novel Hybrid Plasmonic Platform in Sandwich Mode

The recent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has posed a great challenge for the development of ultra-fast methods for virus identification based on sensor principles. We created a structure modeling surface and size of the SARS-CoV-2 virus and used it in comparison with the standard antigen SARS-CoV-2—the receptor-binding domain (RBD) of the S-protein of the envelope of the SARS-CoV-2 virus from the Wuhan strain—for the development of detection of coronaviruses using a DNA-modified, surface-enhanced Raman scattering (SERS)-based aptasensor in sandwich mode: a primary aptamer attached to the plasmonic surface—RBD-covered Ag nanoparticle—the Cy3-labeled secondary aptamer. Fabricated novel hybrid plasmonic structures based on “Ag mirror-SiO2-nanostructured Ag” demonstrate sensitivity for the detection of investigated analytes due to the combination of localized surface plasmons in nanostructured silver surface and the gap surface plasmons in a thin dielectric layer of SiO2 between silver layers. A specific SERS signal has been obtained from SERS-active compounds with RBD-specific DNA aptamers that selectively bind to the S protein of synthetic virion (dissociation constants of DNA-aptamer complexes with protein in the range of 10 nM). The purpose of the study is to systematically analyze the combination of components in an aptamer-based sandwich system. A developed virus size simulating silver particles adsorbed on an aptamer-coated sensor provided a signal different from free RBD. The data obtained are consistent with the theory of signal amplification depending on the distance of the active compound from the amplifying surface and the nature of such a compound. The ability to detect the target virus due to specific interaction with such DNA is quantitatively controlled by the degree of the quenching SERS signal from the labeled compound. Developed indicator sandwich-type systems demonstrate high stability. Such a platform does not require special permissions to work with viruses. Therefore, our approach creates the promising basis for fostering the practical application of ultra-fast, amplification-free methods for detecting coronaviruses based on SARS-CoV-2.

A Combination of Membrane Filtration and Raman-Active DNA Ligand Greatly Enhances Sensitivity of SERS-Based Aptasensors for Influenza A Virus

Biosensors combining the ultrahigh sensitivity of surface-enhanced Raman scattering (SERS) and the specificity of nucleic acid aptamers have recently drawn attention in the detection of respiratory viruses. The most sensitive SERS-based aptasensors allow determining as low as 104 virus particles per mL that is 100-fold lower than any antibody-based lateral flow tests but 10-100-times higher than a routine polymerase chain reaction with reversed transcription (RT-PCR). Sensitivity of RT-PCR has not been achieved in SERS-based aptasensors despite the usage of sophisticated SERS-active substrates. Here, we proposed a novel design of a SERS-based aptasensor with the limit of detection of just 103 particles per ml of the influenza A virus that approaches closely to RT-PCR sensitivity. The sensor utilizes silver nanoparticles with the simplest preparation instead of sophisticated SERS-active surfaces. The analytical signal is provided by a unique Raman-active dye that competes with the virus for the binding to the G-quadruplex core of the aptamer. The aptasensor functions even with aliquots of the biological fluids due to separation of the off-target molecules by pre-filtration through a polymeric membrane. The aptasensor detects influenza viruses in the range of 1·103-5·1010 virus particles per ml.

Greatly Enhanced Single Particle Fluorescence Detection Using High Refractive Index Liquid-Core Waveguides

High sensitivity and easy integration with microfabrication techniques has made silicon photonics one of the leading technologies used to build biosensors for diagnostic applications. Here we introduce a new silicon dioxide based optofluidic platform having a planar solid-core (SC) waveguide orthogonally intersecting a liquid-core (LC) waveguide with high refractive index ZnI2 salt solution as core. This enables both more uniform collection of particle fluorescence by the core mode and its propagation to an off-chip detector. This approach results in ultra-high sensitivity performance, demonstrated by achieving 8X enhancement in signal-to-noise ratio, a 45x increase in detection efficiency, and a 100x lower detection limit of 80 aM of fluorescent nanobeads. This represents a key step towards an ultrasensitive biosensor system for analyzing pathogens at clinical concentrations.

Avidin-biotin complex-based capture coating platform for universal Influenza virus immobilization and characterization

Influenza virus mutates quickly and unpredictably creating emerging pathogenic strains that are difficult to detect, diagnose, and characterize. Conventional tools to study and characterize virus, such as next generation sequencing, genome amplification (RT-PCR), and serological antibody testing, are not adequately suited to rapidly mutating pathogens like Influenza virus where the success of infection heavily depends on the phenotypic expression of surface glycoproteins. Bridging the gap between genome and pathogenic expression remains a challenge. Using sialic acid as a universal Influenza virus binding receptor, a novel virus avidin-biotin complex-based capture coating was developed and characterized that may be used to create future diagnostic and interrogation platforms for viable whole Influenza virus. First, fluorescent FITC probe studies were used to optimize coating component concentrations. Then atomic force microscopy (AFM) was used to profile the surface characteristics of the novel capture coating, acquire topographical imaging of Influenza particles immobilized by the coating, and calculate the capture efficiency of the coating (over 90%) for all four representative human Influenza virus strains tested.

SERS-Based Colloidal Aptasensors for Quantitative Determination of Influenza Virus

Development of sensitive techniques for rapid detection of viruses is on a high demand. Surface-enhanced Raman spectroscopy (SERS) is an appropriate tool for new techniques due to its high sensitivity. DNA aptamers are short structured oligonucleotides that can provide specificity for SERS biosensors. Existing SERS-based aptasensors for rapid virus detection had several disadvantages. Some of them lacked possibility of quantitative determination, while others had sophisticated and expensive implementation. In this paper, we provide a new approach that combines rapid specific detection and the possibility of quantitative determination of viruses using the example of influenza A virus.

A review of aptamer-based SERS biosensors: Design strategies and applications

Surface-enhanced Raman spectroscopy, due to its high sensitivity, unique vibrational fingerprint identification of molecules and easy operation, has been extensively applied in different fields. Aptamers, being the unique single stranded DNA/RNA sequences that can specifically recognize and seize the target analytes, combined with Surface-enhanced Raman spectroscopy (SERS), can offer potent multiplex detection capacity with high specificity and sensitivity. In this review, we summarize and classify the general working strategies of different types of aptamer-based SERS biosensors with diversified protocols which either take aptamer conformational change as intrinsic reporter, or make use of various extrinsic Raman reporters in different sensor designs via on/off approach, sandwich-type and magnetic nanoparticles (NPs)-assisted approach, and catalytic reaction assisted approach with amplification of alternative Raman signals. The advantages, applications and perspectives of these aptamer-based SERS biosensors are also discussed.

Analysis of pressure-driven membrane preconcentration for point-of-care assays

Point-of-care diagnostic devices for both physicians and patients themselves are now ubiquitous, but often not sensitive enough for highly dilute analytes (e.g., pre-symptomatic viral detection). Two primary methods to address this challenge include (1) increasing the sensitivity of molecular recognition elements with greater binding affinity to the analyte or (2) increasing the concentration of the analyte being detected in the sample itself (preconcentration). The latter approach, preconcentration, is arguably more attractive if it can be made universally applicable to a wide range of analytes. In this study, pressure-driven membrane preconcentration devices were developed, and their performance was analyzed for detecting target analytes in biofluids in the form of point-of-care lateral-flow assays (LFAs). The demonstrated prototypes utilize negative or positive pressure gradients to move both water and small interferents (salt, pH) through a membrane filter, thereby concentrating the analyte of interest in the remaining sample fluid. Preconcentration up to 33× is demonstrated for influenza A nucleoprotein with a 5 kDa pore polyethersulfone membrane filter. LFA results are obtained within as short as several minutes and device operation is simple (very few user steps), suggesting that membrane preconcentration can be preferable to more complex and slow conventional preconcentration techniques used in laboratory practice.

Highly sensitive detection of influenza virus with SERS aptasensor

Highly sensitive and rapid technology of surface enhanced Raman scattering (SERS) was applied to create aptasensors for influenza virus detection. SERS achieves 10⁶−10⁹ times signal amplification, yielding excellent sensitivity, whereas aptamers to hemagglutinin provide a specific recognition of the influenza virus. Aptamer RHA0385 was demonstrated to have essentially broad strain-specificity toward both recombinant hemagglutinins and the whole viruses. To achieve high sensitivity, a sandwich of primary aptamers, influenza virus and secondary aptamers was assembled. Primary aptamers were attached to metal particles of a SERS substrate, and influenza viruses were captured and bound with secondary aptamers labelled with Raman-active molecules. The signal was affected by the concentration of both primary and secondary aptamers. The limit of detection was as low as 1 · 10⁻⁴ hemagglutination units per probe as tested for the H3N2 virus (A/England/42/72). Aptamer-based sensors provided recognition of various influenza viral strains, including H1, H3, and H5 hemagglutinin subtypes. Therefore, the aptasensors could be applied for fast and low-cost strain-independent determination of influenza viruses.

Analytical and clinical evaluation of a point-of-care molecular diagnostic system and its influenza A/B assay for rapid molecular detection of the influenza virus

Recently, rapid molecular detection systems have been used for point-of-care testing for the diagnosis of influenza worldwide. Here, we evaluated the performance of the cobas Liat system and the cobas Influenza A/B assay (Liat) using fresh nasopharyngeal samples collected from a Japanese population between December 2017 and February 2018. The performance of the examination was compared with that of antigen testing and a conventional polymerase chain reaction (nested-PCR) method. A total of 159 patients were included in this study, and 77 tested positive using Liat. The concordance rate between Liat and nested PCR was 97.5%. The median time between the ordering of testing and completion of molecular analyses using Liat was 30 min (interquartile range: 28-35 min). The overall sensitivity and specificity of antigen testing were 57.1% and 100%, respectively. The duration from symptom onset to examination did not alter antigen testing sensitivity. The current study demonstrates the high performance of Liat for the rapid molecular identification of the influenza virus.

Coupling multiscale within-host dynamics and between-host transmission with recovery (SIR) dynamics

Multiscale models that link within-host infection to between-host transmission are valuable tools to progress understanding of viral infectious diseases. In this paper, we present two multiscale models that couple within-host infection to a susceptible-infected-recovered (SIR) model. A disease-induced transmission rate bridges the scales from within to between-host. Our stability analysis on the first model (influenza infection) reveals two equilibrium points for the SIR model that describe endemic scenarios where both susceptible and infected cases maintain nonzero population sizes. Consequently, the between-host system has two bifurcations determined by the corresponding basic reproduction number of the within-host and the size of the infected population at the interior equilibrium point. Analysis on the second model (Ebola infection) reveals the limited transient inhibitory effect of antibodies on viral replication, which influences the time window from infection to a potential outbreak. Simulations numerically illustrate our results.

Zoonotic Influenza and Human Health-Part 2: Clinical Features, Diagnosis, Treatment, and Prevention Strategies

Purpose of Review

Zoonotic influenza viruses are those influenza viruses that cross the animal-human barrier and can cause disease in humans, manifesting from minor respiratory illnesses to multiorgan dysfunction. The increasing incidence of infections caused by these viruses worldwide has necessitated focused attention to improve both diagnostic as well as treatment modalities. In this second part of a two-part review, we discuss the clinical features, diagnostic modalities, and treatment of zoonotic influenza, and provide an overview of prevention strategies.

Recent Findings

Illnesses caused by novel reassortant avian influenza viruses continue to be detected and described; most recently, a human case of avian influenza A(H7N4) has been described from China. We continue to witness increasing rates of A(H7N9) infections, with the latest (fifth) wave, from late 2016 to 2017, being the largest to date. The case fatality rate for A(H7N9) and A(H5N1) infections among humans is much higher than that of seasonal influenza infections. Since the emergence of the A(H1N1) 2009 pandemic, and subsequently A(H7N9), testing and surveillance for novel influenzas have become more effective. Various newer treatment options, including peramivir, favipiravir (T-705), and DAS181, and human or murine monoclonal antibodies have been evaluated in vitro and in animal models.

Summary

Armed with robust diagnostic modalities, antiviral medications, vaccines, and advanced surveillance systems, we are today better prepared to face a new influenza pandemic and to limit the burden of zoonotic influenza than ever before. Sustained efforts and robust research are necessary to efficiently deal with the highly mutagenic zoonotic influenza viruses.

Evaluation of NxTAG Respiratory Pathogen Panel and Comparison with xTAG Respiratory Viral Panel Fast v2 and Film Array Respiratory Panel for Detecting Respiratory Pathogens in Nasopharyngeal Aspirates and Swine/Avian-Origin Influenza A Subtypes in Culture Isolates

This study evaluated a new multiplex kit, Luminex NxTAG Respiratory Pathogen Panel, for respiratory pathogens and compared it with xTAG RVP Fast v2 and FilmArray Respiratory Panel using nasopharyngeal aspirate specimens and culture isolates of different swine/avian-origin influenza A subtypes (H2N2, H5N1, H7N9, H5N6, and H9N2). NxTAG RPP gave sensitivity of 95.2%, specificity of 99.6%, PPV of 93.5%, and NPV of 99.7%. NxTAG RPP, xTAG RVP, and FilmArray RP had highly concordant performance among each other for the detection of respiratory pathogens. The mean analytic sensitivity (TCID50/ml) of NxTAG RPP, xTAG RVP, and FilmArray RP for detection of swine/avian-origin influenza A subtype isolates was 0.7, 41.8, and 0.8, respectively. All three multiplex assays correctly typed and genotyped the influenza viruses, except for NxTAG RRP that could not distinguish H3N2 from H3N2v. Further investigation should be performed if H3N2v is suspected to be the cause of disease. Sensitive and specific laboratory diagnosis of all influenza A viruses subtypes is especially essential in certain epidemic regions, such as Southeast Asia. The results of this study should help clinical laboratory professionals to be aware of the different performances of commercially available molecular multiplex RT-PCR assays that are commonly adopted in many clinical diagnostic laboratories.

Windows of opportunity for Ebola virus infection treatment and vaccination

Ebola virus (EBOV) infection causes a high death toll, killing a high proportion of EBOV-infected patients within 7 days. Comprehensive data on EBOV infection are fragmented, hampering efforts in developing therapeutics and vaccines against EBOV. Under this circumstance, mathematical models become valuable resources to explore potential controlling strategies. In this paper, we employed experimental data of EBOV-infected nonhuman primates (NHPs) to construct a mathematical framework for determining windows of opportunity for treatment and vaccination. Considering a prophylactic vaccine based on recombinant vesicular stomatitis virus expressing the EBOV glycoprotein (rVSV-EBOV), vaccination could be protective if a subject is vaccinated during a period from one week to four months before infection. For the case of a therapeutic vaccine based on monoclonal antibodies (mAbs), a single dose might resolve the invasive EBOV replication even if it was administrated as late as four days after infection. Our mathematical models can be used as building blocks for evaluating therapeutic and vaccine modalities as well as for evaluating public health intervention strategies in outbreaks. Future laboratory experiments will help to validate and refine the estimates of the windows of opportunity proposed here.

Development of a realtime RT-PCR assay for the rapid detection of influenza A(H2) viruses

Influenza and other acute respiratory infections are of great concern for public health, causing excessive morbidity and mortality throughout the world. Influenza virus A(H2N2), which caused a pandemic of so called "Asian flu" in 1957 was expelled from the human population by the new pandemic virus subtype H3N2 in 1968, however, influenza A(H2) viruses continue to circulate in wild birds and poultry. The lack of immunity in human population and the continued circulation of influenza A(H2) among animals makes emergence of a new pandemic virus possible. One of the basic techniques of molecular diagnostics of infectious diseases is the realtime polymerase chain reaction (PCR). The aim of this work was to design oligonucleotide primers and probes for the rapid detection of influenza A virus subtype H2 by realtime reverse transcription - polymerase chain reaction (rRT-PCR). Analysis of 539 sequences of influenza A(H2N2) virus hemagglutinin gene from GISAID EpiFlu database revealed conservative regions suitable for use as binding sites for primers and probes. 191 probes were designed and 2 sets of primers and probes (H2-1 and H2-2) were selected for further experimental evaluation. Detection limit of RT-PCR system was 50 copies of DNA per 25 μl reaction when 10-fold dilutions of pCI-neo-H2 plasmid used as template. Analytical specificity of selected sets of primers and probes were tested on wide range of influenza strains and non-influenza respiratory viruses. H2-2 set found to have insufficient specificity detecting seasonal influenza A(H1N1) viruses and was excluded from further analysis. Analytical sensitivity was further tested on vaccine strain A/17/California/66/395 (H2N2) and A/Japan/305/1957 (H2N2), limit of detection for primers-probe set H2-1 was 3.2 (CI95%: 3.07-3.48) lg EID₅₀/ml. Designed primers and probes for the realtime RT-PCR universal detection of influenza A(H2) viruses could be used in clinical trials of vaccines against influenza A(H2) and screening for H2 in cases of unsubtypeable influenza A in humans.

Mycophenolic acid, an immunomodulator, has potent and broad-spectrum in vitro antiviral activity against pandemic, seasonal and avian influenza viruses affecting humans

Immunomodulators have been shown to improve the outcome of severe pneumonia. We have previously shown that mycophenolic acid (MPA), an immunomodulator, has antiviral activity against influenza A/WSN/1933(H1N1) using a high-throughput chemical screening assay. This study further investigated the antiviral activity and mechanism of action of MPA against contemporary clinical isolates of influenza A and B viruses. The 50 % cellular cytotoxicity (CC50) of MPA in Madin Darby canine kidney cell line was over 50 µM. MPA prevented influenza virus-induced cell death in the cell-protection assay, with significantly lower IC50 for influenza B virus B/411 than that of influenza A(H1N1)pdm09 virus H1/415 (0.208 vs 1.510 µM, P=0.0001). For H1/415, MPA interfered with the early stage of viral replication before protein synthesis. For B/411, MPA may also act at a later stage since MPA was active against B/411 even when added 12 h post-infection. Virus-yield reduction assay showed that the replication of B/411 was completely inhibited by MPA at concentrations ≥0.78 µM, while there was a dose-dependent reduction of viral titer for H1/415. The antiviral effect of MPA was completely reverted by guanosine supplementation. Plaque reduction assay showed that MPA had antiviral activity against eight different clinical isolates of A(H1N1), A(H3N2), A(H7N9) and influenza B viruses (IC50 <1 µM). In summary, MPA has broad-spectrum antiviral activity against human and avian-origin influenza viruses, in addition to its immunomodulatory activity. Together with a high chemotherapeutic index, the use of MPA as an antiviral agent should be further investigated in vivo.

Gradient band gap engineered alloyed quaternary/ternary CdZnSeS/ZnSeS quantum dots: an ultrasensitive fluorescence reporter in a conjugated molecular beacon system for the biosensing of influenza virus RNA

Composition-dependent alloyed CdZnSeS/ZnSeS QDs were synthesized and used as a fluorescent reporter in a molecular beacon assay to detect influenza virus RNA.

Infection control preparedness for human infection with influenza A H7N9 in Hong Kong

OBJECTIVE To assess the effectiveness of infection control preparedness for human infection with influenza A H7N9 in Hong Kong. DESIGN A descriptive study of responses to the emergence of influenza A H7N9. SETTING A university-affiliated teaching hospital. PARTICIPANTS Healthcare workers (HCWs) with unprotected exposure (not wearing N95 respirator during aerosol-generating procedure) to a patient with influenza A H7N9. METHODS A bundle approach including active and enhanced surveillance, early airborne infection isolation, rapid molecular diagnostic testing, and extensive contact tracing for HCWs with unprotected exposure was implemented. Seventy HCWs with unprotected exposure to an index case were interviewed especially regarding their patient care activities. RESULTS From April 1, 2013, through May 31, 2014, a total of 126 (0.08%) of 163,456 admitted patients were tested for the H7 gene by reverse transcription-polymerase chain reaction per protocol. Two confirmed cases were identified. Seventy (53.8%) of 130 HCWs had unprotected exposure to an index case, whereas 41 (58.6%) and 58 (82.9%) of 70 HCWs wore surgical masks and practiced hand hygiene after patient care, respectively. Sixteen (22.9%) of 70 HCWs were involved in high-risk patient contacts. More HCWs with high-risk patient contacts received oseltamivir prophylaxis (P=0.088) and significantly more had paired sera collected for H7 antibody testing (P<0.001). Ten (14.3%) of 70 HCWs developed influenza-like illness during medical surveillance, but none had positive results by reverse transcription-polymerase chain reaction. Paired sera was available from 33 of 70 HCWs with unprotected exposure, and none showed seroconversion against H7N9. CONCLUSIONS Despite the delay in airborne precautions implementation, no patient-to-HCW transmission of influenza A H7N9 was demonstrated.

Can newly developed, rapid immunochromatographic antigen detection tests be reliably used for the laboratory diagnosis of influenza virus infections?

Five years ago, the Point-Counterpoint series was launched. The initial article asked about the role of rapid immunochromatographic antigen testing in the diagnosis of influenza A virus 2009 H1N1 infection (D. F. Welch and C. C. Ginocchio, J Clin Microbiol 48:22-25, 2010, http://dx.doi.org/10.1128/JCM.02268-09). Since that article, not only have major changes been made in immunochromatographic antigen detection (IAD) testing for the influenza viruses, but there has also been rapid development of commercially available nucleic acid amplification tests (NAATs) for influenza virus detection. Further, a novel variant of influenza A, H7N9, has emerged in Asia, and H5N1 is also reemergent. In that initial article, the editor of this series, Peter Gilligan, identified two issues that required further consideration. One was how well IAD tests worked in clinical settings, especially in times of antigen drift and shift. The other was the role of future iterations of influenza NAATs and whether this testing would be available in a community hospital setting. James Dunn, who is Director of Medical Microbiology and Virology at Texas Children's Hospital, has extensive experience using IAD tests for diagnosing influenza. He will discuss the application and value of these tests in influenza diagnosis. Christine Ginocchio, who recently retired as the Senior Medical Director, Division of Infectious Disease Diagnostics, North Shore-LIJ Health System, and now is Vice President for Global Microbiology Affairs at bioMérieux, Durham, NC, wrote the initial counterpoint in this series, where she advocated the use of NAATs for influenza diagnosis. She will update us on the commercially available NAAT systems and explain what their role should be in the diagnosis of influenza infection.

Development and Evaluation of Novel Real-Time Reverse Transcription-PCR Assays with Locked Nucleic Acid Probes Targeting Leader Sequences of Human-Pathogenic Coronaviruses

Based on findings in small RNA-sequencing (Seq) data analysis, we developed highly sensitive and specific real-time reverse transcription (RT)-PCR assays with locked nucleic acid probes targeting the abundantly expressed leader sequences of Middle East respiratory syndrome coronavirus (MERS-CoV) and other human coronaviruses. Analytical and clinical evaluations showed their noninferiority to a commercial multiplex PCR test for the detection of these coronaviruses.

An algorithm to diagnose influenza infection: evaluating the clinical importance and impact on hospital costs of screening with rapid antigen detection tests

Rapid antigen detection tests (RADTs) are immunoassays that produce results in 15 min or less, have low sensitivity (50 %), but high specificity (95 %). We studied the clinical impact and laboratory savings of a diagnostic algorithm for influenza infection using RADTs as a first-step technique during the influenza season. From January 15th to March 31st 2014, we performed a diagnostic algorithm for influenza infection consisting of an RADT for all respiratory samples received in the laboratory. We studied all the patients with positive results for influenza infection, dividing them into two groups: Group A with a negative RADT but positive reference tests [reverse transcription polymerase chain reaction (RT-PCR) and/or culture] and Group B with an initial positive RADT. During the study period, we had a total of 1,156 patients with suspicion of influenza infection. Of them, 217 (19 %) had a positive result for influenza: 132 (11 %) had an initial negative RADT (Group A) and 85 (7 %) had a positive RADT (Group B). When comparing patients in Group A and Group B, we found significant differences, as follows: prescribed oseltamivir (67 % vs. 82 %; p = 0.02), initiation of oseltamivir before 24 h (89 % vs. 97 %; p = 0.03), antibiotics prescribed (89 % vs. 67 %; p = <0.01), intensive care unit (ICU) admissions after diagnosis (23 % vs. 14 %; p = 0.05), and need for supplementary oxygen (61 % vs. 47 %; p = 0.01). An influenza algorithm including RADTs as the first step improves the time of administration of proper antiviral therapy, reduces the use of antibiotics and ICU admissions, and decreases hospital costs.

Recombinant influenza A virus hemagglutinin HA2 subunit protects mice against influenza A(H7N9) virus infection

A novel avian influenza A(H7N9) virus has emerged to infect humans in eastern China since 2013. An effective vaccine is needed because of the high mortality despite antiviral treatment and intensive care. We sought to develop an effective vaccine for A(H7N9) virus. The HA2 subunit was chosen as the vaccine antigen because it is highly conserved among the human A(H7N9) virus strains. Moreover, in silico analysis predicted two immunogenic regions within the HA2 subunit that may contain potential human B-cell epitopes. The HA2 fragment was readily expressed in Escherichia coli. In BALB/c mice, intraperitoneal immunization with two doses of HA2 with imiquimod (2-dose-imiquimod) elicited the highest geometric mean titer (GMT) of anti-HA2 IgG (12699), which was greater than that of two doses of HA2 without imiquimod (2-dose-no-adjuvant) (6350), one dose of HA2 with imiquimod (1-dose-imiquimod) (2000) and one dose of HA2 without imiquimod (1-dose-no-adjuvant) (794). The titer of anti-HA2 IgG was significantly higher in the 1-dose-imiquimod group than the 1-dose-no-adjuvant group. Although both hemagglutination inhibition titers and microneutralization titers were below 10, serum from immunized mice showed neutralizing activity in a fluorescent focus microneutralization assay. In a viral challenge experiment, the 2-dose-imiquimod group had the best survival rate (100 %), followed by the 2-dose-no-adjuvant group (90 %), the 1-dose-imiquimod group (70 %) and the 1-dose-no-adjuvant group (40 %). The 2-dose-imiquimod group also had significantly lower mean pulmonary viral loads than the 1-dose-imiquimod, 1-dose-no-adjuvant and non-immunized groups. This recombinant A(H7N9)-HA2 vaccine should be investigated as a complement to egg- or cell-based live attenuated or subunit influenza vaccines.

Viral lung infections: epidemiology, virology, clinical features, and management of avian influenza A(H7N9)

PURPOSE OF REVIEW

The avian influenza A(H7N9) virus has jumped species barrier and caused severe human infections. Here, we present the virological features relevant to clinical practice, and summarize the epidemiology, clinical findings, diagnosis, treatment, and preventive strategies of A(H7N9) infection.

RECENT FINDINGS

As of 18 February 2014, A(H7N9) virus has caused 354 infections in mainland China, Taiwan, and Hong Kong with a case-fatality rate of 32%. Elderly men were most affected. Most patients acquired the infection from direct contact with poultry or from a contaminated environment, although person-to-person transmission has likely occurred. A(H7N9) infection has usually presented with severe pneumonia, often complicated by acute respiratory distress syndrome and multiorgan failure. Mild infections have been reported in children and young adults. Nasopharyngeal aspirate and sputum samples should be collected for diagnosis, preferably using reverse transcriptase-PCR. Early treatment with neuraminidase inhibitors improved survival, but the efficacy of antivirals was hampered by resistant mutants. The closure of live poultry markets in affected areas has significantly contributed to the decline in the incidence of human cases.

SUMMARY

The emergence of A(H7N9) virus represents a significant health threat. High vigilance is necessary so that appropriate treatment can be instituted for the patient and preventive measures can be implemented.

Emergence in China of human disease due to avian influenza A(H10N8)--cause for concern?

In December 2013, China reported the first human case of avian influenza A(H10N8). A 73-year-old female with chronic diseases who had visited a live poultry market succumbed with community-acquired pneumonia. While human infections with avian influenza viruses are usually associated with subtypes prevalent in poultries, A(H10N8) isolates were mostly found in migratory birds and only recently in poultries. Although not possible to predict whether this single intrusion by A(H10N8) is an accident or the start of another epidemic like the preceding A(H7N9) and A(H5N1), several features suggest that A(H10N8) is a potential threat to humans. Recombinant H10 could attach to human respiratory epithelium, and A(H10N4) virus could cause severe infections in minks and chickens. A(H10N8) viruses contain genetic markers for mammalian adaptation and virulence in the haemagglutinin (A135T, S138A[H3 numbering]), M1(N30D, T215A), NS1(P42S) and PB2(E627K) protein. Studies on this human A(H10N8) isolate will reveal its adaptability to humans. Clinicians should alert the laboratory to test for A(H5,6,7,9,10) viruses in patients with epidemiological exposure in endemic geographical areas especially when human influenza A(H1,3) and B are negative. Vigilant virological and serological surveillance for A(H10N8) in human, poultry and wild bird is important for following the trajectory of this emerging influenza virus.

Rapid and sensitive detection of H7N9 avian influenza virus by use of reverse transcription-loop-mediated isothermal amplification

An epidemic of human H7N9 influenza virus infection recently emerged in China whose clinical features include high mortality and which has also resulted in serious economic loss. The novel reassortant avian-origin influenza A (H7N9) virus which was the causative agent of this epidemic raised the possibility of triggering a large-scale influenza pandemic worldwide. It seemed likely that fast molecular detection assays specific for this virus would be in great demand. Here, we report a one-step reverse transcription-loop-mediated isothermal amplification (RT-LAMP) method for rapid detection of the hemagglutinin (HA) and neuraminidase (NA) genes of H7N9 virus, the minimum detection limit of which was evaluated using in vitro RNA transcription templates. In total, 135 samples from clinical specimens (from either patients or poultry) were tested using this method in comparison with the real-time PCR recommended by the World Health Organization (WHO). Our results showed that (i) RT-LAMP-based trials can be completed in approximately 12 to 23 min and (ii) the detection limit for the H7 gene is around 10 copies per reaction, similar to that of the real-time PCR, whereas the detection limit for its counterpart the N9 gene is 5 copies per reaction, a 100-fold-higher sensitivity than the WHO-recommended method. Indeed, this excellent performance of our method was also validated by the results for a series of clinical specimens. Therefore, we believe that the simple, fast, and sensitive method of RT-LAMP might be widely applied for detection of H7N9 infections and may play a role in prevention of an influenza pandemic.

The emergence of influenza A H7N9 in human beings 16 years after influenza A H5N1: a tale of two cities

Infection with either influenza A H5N1 virus in 1997 or avian influenza A H7N9 virus in 2013 caused severe pneumonia that did not respond to typical or atypical antimicrobial treatment, and resulted in high mortality. Both viruses are reassortants with internal genes derived from avian influenza A H9N2 viruses that circulate in Asian poultry. Both viruses have genetic markers of mammalian adaptation in their haemagglutinin and polymerase PB2 subunits, which enhanced binding to human-type receptors and improved replication in mammals, respectively. Hong Kong (affected by H5N1 in 1997) and Shanghai (affected by H7N9 in 2013) are two rapidly flourishing cosmopolitan megacities that were increasing in human population and poultry consumption before the outbreaks. Both cities are located along the avian migratory route at the Pearl River delta and Yangtze River delta. Whether the widespread use of the H5N1 vaccine in east Asia-with suboptimum biosecurity measures in live poultry markets and farms-predisposed to the emergence of H7N9 or other virus subtypes needs further investigation. Why H7N9 seems to be more readily transmitted from poultry to people than H5N1 is still unclear.

Detection of influenza H7N9 virus: all molecular tests are not equal

The recent emergence of influenza A virus (H7N9) emphasizes the need for its rapid detection. While commercial nucleic acid amplification tests (NAATs) are commonly used to detect seasonal influenza virus, this study demonstrated that the analytical sensitivity of commercial assays is highly variable compared to that of CDC-based in-house NAATs for the detection of H7N9.