Evaluation of a commercial ELISA for detecting Norwalk-like virus antigen in faeces

Advances and Future Perspective on Detection Technology of Human Norovirus

Human norovirus (HuNoV) is a food-borne pathogen that causes acute gastroenteritis in people of all ages worldwide. However, no approved vaccines and antiviral drugs are available at present. Therefore, the development of accurate and rapid detection technologies is important in controlling the outbreak of HuNoVs. This paper reviewed the research progress on HuNoV detection, including immunological methods, molecular detection and biosensor technology. Immunological methods and molecular detection technologies are still widely used for HuNoV detection. Furthermore, biosensors will become an emerging developmental direction for the rapid detection of HuNoVs because of their high sensitivity, low cost, easy operation and suitability for onsite detection.

Norovirus detection in water samples at the level of single virus copies per microliter using a smartphone-based fluorescence microscope

Norovirus is a widespread public health threat and has a very low infectious dose. This protocol presents the extremely sensitive mobile detection of norovirus from water samples using a custom-built smartphone-based fluorescence microscope and a paper microfluidic chip. Antibody-conjugated fluorescent particles are immunoagglutinated and spread over the paper microfluidic chip by capillary action for individual counting using a smartphone-based fluorescence microscope. Smartphone images are analyzed using intensity- and size-based thresholding for the elimination of background noise and autofluorescence as well as for the isolation of immunoagglutinated particles. The resulting pixel counts of particles are correlated with the norovirus concentration of the tested sample. This protocol provides detailed guidelines for the construction and optimization of the smartphone- and paper-based assay. In addition, a 3D-printed enclosure is presented to incorporate all components in a dark environment. On-chip concentration and the assay of higher concentrations are presented to further broaden the assay range. This method is the first to be presented as a highly sensitive mobile platform for norovirus detection using low-cost materials. With all materials and reagents prepared, a single standard assay takes under 20 min. Although the method described is used for detection of norovirus, the same protocol could be adapted for detection of other pathogens by using different antibodies.

Human and Animal Viruses in Food (Including Taxonomy of Enteric Viruses)

In recent years, there has been an increase in the incidence of foodborne diseases worldwide, with viruses now being recognized as a major cause of these illnesses. The most common viruses implicated in foodborne disease are enteric viruses, which are found in the human gastrointestinal tract, excreted in human feces and transmitted by the fecal-oral route. Many different viruses are found in the gastrointestinal tract but not all are recognized as foodborne pathogens. The diseases caused by enteric viruses fall into three main types: gastroenteritis, enterically transmitted hepatitis, and illnesses that can affect other parts of the body such as the eye, the respiratory system and the central nervous system leading to conjunctivitis, poliomyelitis, meningitis and encephalitis. Viral pathogens excreted in human feces include noroviruses, sapoviruses, enteroviruses, adenoviruses, hepatitis A virus (HAV), hepatitis E virus (HEV), rotaviruses, and astroviruses. Most of these viruses have been associated with foodborne disease outbreaks. Noroviruses and HAV are commonly identified as foodborne causes of gastroenteritis and acute hepatitis, respectively.

Gastrointestinal Infections

Establishing a specific etiology for gastrointestinal infections can be challenging because of the common clinical features and wide variety of causative microorganisms. In many cases, the etiologic agent cannot be determined using traditional diagnostic methods and may result in unnecessary antibiotic use or prolonged periods of illness. Molecular tests provide many advantages over traditional laboratory methods but, with the exception of a few analytes, are still largely in the developmental phase for gastrointestinal pathogens and are not widely used. The main advantages of molecular tests include increased sensitivity and the ability to detect agents which will not grow in culture. To test for all possible gastrointestinal pathogens at one time would require a large panel that would include a variety of bacterial, viral and parasitic agents. Challenges inherent in developing diagnostic molecular panels include ensuring that all variants of a particular microorganism can be detected as well as the rapid evolution of pathogens. In this chapter, the diagnostic merit of molecular tests as well as available tests will be presented for the major groups of gastrointestinal pathogens.

Laboratory diagnosis of noroviruses: present and future

Norovirus is an important cause of gastroenteritis outbreaks globally and the most prevalent cause of sporadic gastroenteritis in many regions. Rapid and accurate identification of causative viral agents is critical for outbreak investigation, disease surveillance, and management. Because norovirus is not cultivable and has a highly diversified and variable genome, it is difficult to develop diagnostic assays. Detection methods have evolved from electron microscopy to conventional end-point reverse transcription polymerase chain reaction (RT-PCR), immunoassay, real-time RT-PCR, other molecular technologies, and nanotechnology array-based assays. The status and features of various testing methods are summarized in this review.

Norovirus

Norovirus, an RNA virus of the family Caliciviridae, is a human enteric pathogen that causes substantial morbidity across both health care and community settings. Several factors enhance the transmissibility of norovirus, including the small inoculum required to produce infection (<100 viral particles), prolonged viral shedding, and its ability to survive in the environment. In this review, we describe the basic virology and immunology of noroviruses, the clinical disease resulting from infection and its diagnosis and management, as well as host and pathogen factors that complicate vaccine development. Additionally, we discuss overall epidemiology, infection control strategies, and global reporting efforts aimed at controlling this worldwide cause of acute gastroenteritis. Prompt implementation of infection control measures remains the mainstay of norovirus outbreak management.

Identification of human single-chain antibodies with broad reactivity for noroviruses

Norovirus infections are a common cause of gastroenteritis and new methods to rapidly diagnose norovirus infections are needed. The goal of this study was to identify antibodies that have broad reactivity of binding to various genogroups of norovirus. A human scFv phage display library was used to identify two antibodies, HJT-R3-A9 and HJT-R3-F7, which bind to both genogroups I and II norovirus virus-like particles (VLPs). Mapping experiments indicated that the HJT-R3-A9 clone binds to the S-domain while the HJT-R3-F7 clone binds the P-domain of the VP1 capsid protein. In addition, a family of scFv antibodies was identified by elution of phage libraries from the GII.4 VLP target using a carbohydrate that serves as an attachment factor for norovirus on human cells. These antibodies were also found to recognize both GI and GII VLPs in enzyme-linked immunosorbent assay (ELISA) experiments. The HJT-R3-A9, HJT-R3-F7 and scFv antibodies identified with carbohydrate elution were shown to detect antigen from a clinical sample known to contain GII.4 norovirus but not a negative control sample. Finally, phages displaying the HJT-R3-A9 scFv can be used directly to detect both GI.1 and GII.4 norovirus from stool samples, which has the potential to simplify and reduce the cost of diagnostics based on antibody-based ELISA methods.

A comparison of the efficiency of ELISA and selected primer sets to detect Norovirus isolates in southern Ireland over a four-year period (2002-2006): variation in detection rates and evidence for continuing predominance of NoV GII.4 genotype

Norovirus (NoV) gastroenteritis occurs in all age groups and is the most common cause of gastroenteritis in the community. However, detection methods and rates vary widely, and few data are available to compare these, particularly in Ireland. Detection of noroviruses through antigen and molecular-based strategies was carried out on 135 suspected NoV-positive samples, collected over the course of three NoV outbreaks, from 2002 to 2006, in the southern region of Ireland. A commercially available ELISA and a panel of six primer sets were evaluated to determine their suitability for NoV detection in Irish clinical samples. The key findings of this study were the detection of both GGI and GGII noroviruses by ELISA, but the detection of only GGII noroviruses by RT-PCR. In addition to this, a variation in the levels of detection from 9.4 % to 17.3 % was observed for conventional PCR assays, while a detection rate of 46.3 % was observed for the real-time PCR assay. A proportion (17.8 %) of samples were found to be negative by all detection strategies, suggesting the possibility of reporting false positives for these samples or low-copy positives that do not often repeat. Sequencing information from selected samples also revealed nucleotide polymorphisms, compromising efficient primer binding in the case of one primer pairing. Phylogenetic analysis of the partial polymerase gene identified NoV GII.4 as the dominant genotype, in accordance with previous NoV studies in Ireland. Investigating the NoV diversity of the circulating strains and the dynamics of strain replacement is important to better assess the efficacy of future NoV vaccines and to facilitate the early detection of changes in circulating NoV strains.

Investigating norovirus removal by microfiltration, ultrafiltration, and precoagulation-microfiltration processes using recombinant norovirus virus-like particles and real-time immuno-PCR

The removal of microorganisms by drinking water treatment processes has been widely investigated in laboratory-scale experiments using artificially propagated microorganisms. However, this approach cannot be applied to norovirus removal, because this virus does not grow in cell or organ culture, and this fact has hampered our ability to investigate its behavior during drinking water treatment. To overcome this difficulty, our research group previously used recombinant norovirus virus-like particles (rNV-VLPs), which consist of an artificially expressed norovirus capsid protein, in laboratory-scale drinking water treatment experiments. However, the enzyme-linked immunosorbent assay (ELISA) method generally used to detect rNV-VLPs is not sensitive enough to evaluate high removal ratios such as those obtained by ultrafiltration (UF). We therefore developed and applied a real-time immuno-polymerase chain reaction (iPCR) assay for rNV-VLP quantification to investigate norovirus removal by microfiltration (MF), UF, and hybrid precoagulation-MF processes. The rNV-VLP detection limit with the developed iPCR assay was improved at least 1000-fold compared with ELISA. Whereas MF with a nominal pore size of 0.1 μm could not eliminate NV-VLPs, a 4-log reduction was achieved by UF with a molecular weight cutoff of 1 kDa. When MF was combined with precoagulation (≥10 μmol-Fe/L for ferric chloride; ≥20 μmol-Al/L for polyaluminum chloride; ≥40 μmol-Al/L for alum), the performance of the hybrid process in eliminating rNV-VLPs was greater than that achieved by the 1 kDa UF. For all processes, the removal ratios of the bacteriophages MS2 and Qβ were greater than the rNV-VLP removal ratios by 1-2 logs, so neither bacteriophage can be recommended as a possible conservative surrogate for predicting the behavior of native NV during these processes.

Virus-like Particle Vaccines for Norovirus Gastroenteritis

Gastroenteritis (GE) and its associated diarrheal diseases remain as one of the top causes of death in the world. Noroviruses (NoVs) are a group of genetically diverse RNA viruses that cause the great majority of nonbacterial gastroenteritis in humans. However, there is still no vaccine licensed for human use to prevent NoV GE. The lack of a tissue culture system and a small animal model further hinders the development of NoV vaccines.

Virus-like particles (VLPs) that mimic the antigenic architecture of authentic virions, however, can be produced in insect, mammalian, and plant cells by the expression of the capsid protein. The particulate nature and high-density presentation of viral structure proteins on their surface render VLPs as a premier vaccine platform with superior safety, immunogenicity, and manufacturability. Therefore, this chapter focuses on the development of effective NoV vaccines based on VLPs of capsid proteins. The expression and structure of NoV VLPs, especially VLPs of Norwalk virus, the prototype NoV, are extensively discussed. The ability of NoV VLPs in stimulating a potent systemic and mucosal anti-NoV immunity through oral and intranasal delivery in mice is presented.

The advantages of plant expression systems as a novel production platform for VLP-based NoV vaccines are discussed in light of their cost-effectiveness, production speed, and scalability. Recent achievements from the first successful demonstration of NoV VLP production in plant expression system under the current Good Manufacture Practice (cGMP) regulation by the US Food and Drug Administration (FDA) are detailed.

Moreover, results of human clinical trials demonstrating the safety and efficacy of insect and plant-derived NoV VLPs are also presented. Due to the diversity of capsid protein among different NoV strains and its rapid antigenic drift, we speculate that vaccine development should focus on multivalent VLP vaccines derived from capsid proteins of the most prevalent strains. With the very recent approval of the first plant-made biologics by the FDA, we also speculate that plant-based production systems will play an important role in manufacturing such multivalent VLP-based NoV vaccines.

New approaches in microbial pathogen detection

Viruses are common causes of foodborne outbreaks. Viral diseases have low fatality rates but transmission to humans via food is important due to the high probability of consuming fecally contaminated food or water because of poor food handling. Because of the low infectious doses of some foodborne viruses, there is a need for standardization and the development of new sensitive methods for detecting viruses. The focus is on molecular and non-molecular approaches, and emerging methods for the detection of foodborne viruses. The detection of noroviruses, hepatitis A and E viruses, rotaviruses and adenoviruses will be discussed. The chapter will conclude with insights into future research directions.

Evaluation of 4 immunochromatographic tests for rapid detection of norovirus in faecal samples

BACKGROUND

The rapid detection of noroviruses is essential to implement measures to reduce the rapid spread of gastroenteritis infections they cause, notably in institutions.

OBJECTIVES

To evaluate 4 rapid immunochromatographic tests: RIDA(®)QUICK Norovirus, ImmunoCardSTAT!(®) Norovirus, NOROTOP(®) and SD BIOLINE NOROVIRUS by determining their sensitivity and specificity on a large panel of samples representing 11 genotypes of norovirus genogroup I and 14 of genogroup II, and their cross-reactivity with other enteric viruses.

STUDY DESIGN

Thawed stool samples containing norovirus genogroup I or II or other enteric viruses, and negative samples, were tested by the 4 assays and compared to the reference standard RT-PCR. Fresh stool samples were also tested by RIDA(®)QUICK.

RESULTS

The sensitivity of RIDA(®)QUICK, ImmunoCardSTAT!(®), NOROTOP(®) and SD BIOLINE for the detection of norovirus genogroup I on thawed samples was 17%, 26%, 52% and 23%, respectively. For genogroup II, the sensitivity was 64%, 39%, 50% and 54%, respectively. For GII.4, the main circulating genotype, the sensitivity was 78%, 59%, 61% and 67%, respectively. For all tests, the specificity was 100% and no cross-reactivity with other enteric viruses was observed. The sensitivity of RIDA(®)QUICK on fresh stool samples positive for GII.4 was 71%.

CONCLUSIONS

Knowing that most gastroenteritis cases are due to GII.4, the immunochromatographic tests may be useful for preliminary screening, notably in outbreaks. However, negative samples need to be tested using RT-PCR methods.

Norovirus diagnostics: options, applications and interpretations

Noroviruses are a frequent cause of both acute gastroenteritis and outbreaks of gastroenteritis. Infection is usually self-limiting although it has been associated with mortality in children in the developing world and in vulnerable groups such as immunodeficient or immunosuppressed and elderly patients elsewhere. Diagnostic tests may be useful in preventing or limiting the spread and duration of outbreaks, and are needed to define norovirus-associated morbidity and mortality. However, the interpretation of test results should take account of the limitations of the different tests currently available. Therefore, the clinical, immunological and molecular tests available for norovirus detection have been reviewed. Early recognition of cases (clinical diagnoses) together with confirmation by sensitive and specific laboratory tests may contribute to reducing the spread of norovirus within hospitals. Syndromic testing that includes multiple or multiplex assays for the detection of viral, bacterial and parasitic pathogens with the inclusion of control groups are likely to better define norovirus-associated morbidity and mortality in low- and middle-income countries.

Structural basis for broad detection of genogroup II noroviruses by a monoclonal antibody that binds to a site occluded in the viral particle

Human noroviruses are genetically and antigenically highly divergent. Monoclonal antibodies raised in mice against one kind of norovirus virus-like particle (VLP), however, were found to have broad recognition. In this study, we present the crystal structure of the antigen-binding fragment (Fab) for one of these broadly reactive monoclonal antibodies, 5B18, in complex with the capsid-protruding domain from a genogroup II genotype 10 (GII.10) norovirus at 3.3-Å resolution and, also, the cryo-electron microscopy structure of the GII.10 VLP at ∼10-Å resolution. The GII.10 VLP structure was more similar in overall architecture to the GV.1 murine norovirus virion than to the prototype GI.1 human norovirus VLP, with the GII.10 protruding domain raised ∼15 Å off the shell domain and rotated ∼40° relative to the GI.1 protruding domain. In the crystal structure, the 5B18 Fab bound to a highly conserved region of the protruding domain. Based on the VLP structure, this region is involved in interactions with other regions of the capsid and is buried in the virus particle. Despite the occluded nature of the recognized epitope in the VLP structure, enzyme-linked immunosorbent assay (ELISA) binding suggested that the 5B18 antibody was able to capture intact VLPs. Together, the results provide evidence that the norovirus particle is capable of extreme conformational flexibility, which may allow for antibody recognition of conserved surfaces that would otherwise be buried on intact particles.

Frequency and phylogeny of norovirus in diarrheic children in Istanbul, Turkey

BACKGROUND

Norovirus (NoV) is recognised as one of the most common causes of foodborne infections. Contaminated shellfish, food, water and hospitals are well documented sources of the virus.

OBJECTIVE

NoV in diarrheic children has not previously been investigated in Istanbul, Turkey, hence the aim of this study was to detect and investigate the frequency and phylogeny of human NoV genogroups I and II in children with acute gastroenteritis.

STUDY DESIGN

238 stool samples were collected from diarrheic children from 2 hospitals (Cerrahpasa Medical School and Haseki) in Istanbul and analysed by ELISA, RT-PCR and real-time RT-PCR using both SYBR Green and probe-based assays for human NoV. Primers targeting the RNA-polymerase gene were used for RT-PCR to allow DNA sequencing of Turkish NoV strains and phylogenetic analysis to be performed.

RESULTS

NoV GII was detected in 36 (15.1%) of 238 samples by SYBR Green real-time RT-PCR, 10.9% by a probe-based real-time RT-PCR and 10.5% by ELISA (Ridascreen). Genogroup II (GII) the Turkish NoVs clustered with including GII4 (72.2%), GII16 (5.5%), GIIb (16.7%) and GIIe (5.5%). Two variants of GII4 (GII4-2006b and GII4-2008), GII16 and recombinant noroviruses (GIIb and GIIe) were identified.

CONCLUSION

This study shows a high frequency and genetic diversity of NoV GII infections in children with acute gastroenteritis in Istanbul, Turkey.

Recognition and prevention of hospital-associated enteric infections in the intensive care unit

The objectives of this article were to review the causes and extent of hospital-associated infectious diarrhea and associated risks in the general hospital ward and intensive care unit (ICU), to compare microorganisms with similar symptoms to aid in recognition that will lead to timely and appropriate treatment and control measures, and to propose infection prevention protocols that could decrease human process errors in the ICU. This literature review describes epidemiology, comparison of microbial characteristics for potential hospital-associated enteric pathogens, diagnosis, and prevention, especially if important in the ICU, and particularly in regard to Clostridium difficile. Enteric organisms that most commonly cause hospital-associated infectious diarrhea in acute care settings and the ICU are C. difficile, rotavirus, and norovirus, although others may also be important, particularly in developing countries. To recognize and control infectious diarrhea successfully in the ICU, intensivists should be aware that epidemiology, risks, and prevention measures may differ between these microorganisms. In addition, intensivists should be ready to implement systems changes related to notification, isolation precautions and prevention, and environmental cleaning in the ICU.

Diagnostic accuracy and analytical sensitivity of IDEIA Norovirus assay for routine screening of human norovirus

Noroviruses (NoVs) are recognized as the leading cause of epidemic and sporadic acute gastroenteritis. Early detection of NoV is crucial to control the spread of the disease. In this study, we evaluated the diagnostic accuracy, analytical sensitivity, and analytical reactivity of the IDEIA Norovirus assay (an enzyme immunoassay [EIA]) in a prospective and retrospective study design. A total of 557 prospectively collected fecal samples and a panel of 97 archived fecal samples, including 21 different GI and GII genotypes, were tested by conventional reverse transcription-PCR (RT-PCR)/bidirectional sequencing, real-time RT-PCR, and electron microscopy. The sensitivity and specificity of the EIA were 57.6% and 91.9%, respectively. The sensitivity for detecting NoV in fecal samples from outbreaks improved from 44.1% when three samples were tested to 76.9% when five samples per outbreak were tested. The EIA was able to detect strains from 7 GI and 11 GII genotypes. The analytical sensitivity of the EIA was 3.1 x 10(6) and 1.6 x 10(7) virus particles g(-1) of fecal sample for NoV GI and GII strains, respectively. Most GII samples positive by EIA had a threshold cycle (C(T)) of <26.5, and 50% of the GII samples negative by EIA had a C(T) of >25.6, suggesting that, although strains from genotypes GI.8, GII.10, and GII.16 were not detected, the low sensitivity of the EIA is primarily caused by low virus concentration. In conclusion, the current EIA may be of use as a rapid screening test during a norovirus outbreak investigation when multiple fecal samples are available; however, sporadic samples should be tested by molecular methods.

Real-time molecular beacon NASBA for rapid and sensitive detection of norovirus GII in clinical samples

To improve the sensitivity and efficiency of the real-time nucleic acid sequence based amplification (NASBA) assay targeting the open reading frame 1–2 (ORF1–ORF2) junction of the norovirus (NoV) genome, a selection of clinical samples were analyzed. The assay results were compared with those of TaqMan and conventional reverse transcription PCR (RT-PCR) and a commercial enzyme-linked immunoassay (ELISA) for the specific detection of GII NoV in 96 fecal samples. Based on end-point dilution, the two real-time assays had similar sensitivities (0.01 particle detectable units), two log10cycles greater than that of conventional RT-PCR. GII NoV was detected in 88.54% of the samples by real-time NASBA, in 86.46% by TaqMan RT-PCR, in 81.25% by conventional RT-PCR, and in 65.7% by ELISA. The two real-time assays were in agreement for 88.5% of the samples. These results demonstrate that real-time NASBA with a molecular beacon probe is highly sensitive, accurate, and specific for NoV detection in clinical samples. Applying this technique to samples with complex matrix and low viral loads, such as food and environmental samples, could be useful for the detection of NoVs and will improve the prevention of NoV outbreaks.

Of gastro and the gold standard: evaluation and policy implications of norovirus test performance for outbreak detection

Background

The norovirus group (NVG) of caliciviruses are the etiological agents of most institutional outbreaks of gastroenteritis in North America and Europe. Identification of NVG is complicated by the non-culturable nature of this virus, and the absence of a diagnostic gold standard makes traditional evaluation of test characteristics problematic.

Methods

We evaluated 189 specimens derived from 440 acute gastroenteritis outbreaks investigated in Ontario in 2006–07. Parallel testing for NVG was performed with real-time reverse-transcriptase polymerase chain reaction (RT²-PCR), enzyme immunoassay (EIA) and electron microscopy (EM). Test characteristics (sensitivity and specificity) were estimated using latent class models and composite reference standard methods. The practical implications of test characteristics were evaluated using binomial probability models.

Results

Latent class modelling estimated sensitivities of RT²-PCR, EIA, and EM as 100%, 86%, and 17% respectively; specificities were 84%, 92%, and 100%; estimates obtained using a composite reference standard were similar. If all specimens contained norovirus, RT²-PCR or EIA would be associated with > 99.9% likelihood of at least one test being positive after three specimens tested. Testing of more than 5 true negative specimens with RT²-PCR would be associated with a greater than 50% likelihood of a false positive test.

Conclusion

Our findings support the characterization of EM as lacking sensitivity for NVG outbreaks. The high sensitivity of RT²-PCR and EIA permit identification of NVG outbreaks with testing of limited numbers of clinical specimens. Given risks of false positive test results, it is reasonable to limit the number of specimens tested when RT²-PCR or EIA are available.

Broadly reactive TaqMan assay for real-time RT-PCR detection of rotavirus in clinical and environmental samples. JIN2@cdc.gov

Rotaviruses are enteric pathogens responsible for a significant burden of disease, especially in children, through person-to-person transmission and exposure to contaminated food and water. In the present study, a TaqMan probe-based real-time reverse transcriptase (RT) polymerase chain reaction (PCR) assay was developed and validated for sensitive and specific detection and quantification of rotavirus for the routine screening of clinical and environmental samples. The assay primers and probes were designed to target the non-structural protein region 3 (NSP3) of rotavirus. The rotavirus real-time RT-PCR assay was found to be specific to rotavirus, but broadly reactive to rotavirus genogroups 1-4, 9, 10 and 12. Specificity testing did not identify any cross-reactivity of the assay with a panel of 36 non-rotavirus enteric virus specimens. The sensitivity of the assay was determined using quantified rotavirus stocks and a plasmid DNA stock. Estimated detection limits in reagent-grade water were five genome equivalent copies (GEC) per reaction and two to four rotavirus particles per reaction. The sensitivity of the assay for detecting rotaviruses in environmental water samples was found to be six virus particles per reaction. The rotavirus real-time RT-PCR assay was effective in detecting rotavirus in all 79 stool specimens obtained from a hospital in India. The results of this study demonstrate that the real-time RT-PCR assay for rotavirus is broadly reactive, specific, and sensitive for detection of rotaviruses in clinical specimens and water samples.

Acute gastroenteritis outbreaks in Catalonia, Spain: norovirus versus Salmonella

OBJECTIVE

To describe the epidemiology of norovirus (NV) and Salmonella gastroenteritis outbreaks in Catalonia between 15 October 2004 and 30 October 2005.

MATERIAL AND METHODS

Epidemiological data were obtained from outbreak reports. The aetiologic agent was investigated by culture for enteric bacteria, enzyme immunoanalyses, reverse transcription polymerase chain reaction (RT-PCR) and molecular epidemiology genotyping for NV. The chi(2) test was used to compare proportions. Incidence rates and their confidence intervals (CI) were calculated assuming a Poisson distribution.

RESULTS

A total of 225 acute gastroenteritis (AG) outbreaks were reported, with 3436 persons affected and 115 hospitalized. Sixty outbreaks (27%) accounting for 1791 cases (52%) were caused by NV, with an attack rate (AR) of 34.7% and a hospitalization rate (HR) of 0.2%. Seventy- four outbreaks (33%) were caused by Salmonella spp., affecting 646 persons (18.8% (AR 45.6% and HR 13.7%)). The difference in AR between Salmonella spp. and NV was statistically significant (odds ratio (OR) 1.57; 95% CI: 1.39-1.78; p < 0.001). The median number of affected persons per outbreak was 3-fold higher for NV (15 (2-174)) than for Salmonella (5 (2-44)). The incidence rate of AG cases associated with NV outbreaks was significantly higher (24.9 per 100,000 persons/year (95% CI: 23.7-26.1)) than for those associated with Salmonella (5(2-44)) outbreaks (9.2 per 100,000 persons/year (95% CI: 8.5-9.9)).

CONCLUSIONS

The disease burden and impact of NV highlight the importance of timely notification and investigation of outbreaks and the development and implementation of preventive measures, such as health and safety education for caregivers and food handlers in order to reduce the incidence of infections.

Apparently non-specific results found using a norovirus antigen immunoassay for fecal specimens from neonates

Norovirus is increasingly recognized as a frequent cause of non-bacterial gastroenteritis. Despite a 10-fold increase in the number of cases reported following the availability of enzyme immunoassays, there are no reports yet from preterm neonates. We report on a sudden clustering of antigen-positive enzyme immuno assays results in a level III neonatal intensive care unit, involving 22 of 43 infants screened. Although antigen-positive samples were significantly associated with bloody stools (P<0.001) and gastric residues (P<0.02), norovirus infection could not be confirmed by reverse-transcriptase polymerase chain reaction or electron microscopy. We question the validity of the so called norovirus-specific antigen assays and warn against overreacting to positive enzyme immunoassays results without reverse-transcriptase polymerase chain reaction confirmation especially in the neonatal setting.

Detection of viral agents of gastroenteritis: Norovirus, Sapovirus and Astrovirus

Norovirus, Sapovirus and Astrovirus are causative agents of viral gastroenteritis affecting all age groups, but most frequently the young, the elderly and persons in semi-closed communities such as hospitals, nursing homes, military bases and cruise ships. The sensitive and rapid detection of causative agents of viral gastroenteritis is key to the effective implementation of infection control systems. Traditional detection methods such as electron microscopy and antigen detection assays lack sensitivity. The detection of gastrointestinal viruses by molecular methods has resulted in increased levels of detection, and enables the epidemiological investigation of viral strains. The significant diversity of gastrointestinal viruses, in particular Norovirus and Sapovirus, are compounded by increasing reports of virus recombination, and pose an ongoing challenge to the development of sensitive and specific molecular detection assays.

Probabilities in norovirus outbreak diagnosis

BACKGROUND

Noroviruses are recognized as the most common cause of outbreaks of acute gastroenteritis. Yet, diagnostic testing for norovirus is based mostly on RNA detection by RT-PCR, which is not widely available. While antigen detection tests (ELISAs) are easier to perform, they are in general less sensitive.

OBJECTIVES

Our aim was to provide a scientific basis for declaring norovirus as the causative agent of an outbreak of acute gastroenteritis.

STUDY DESIGN

Statistical analysis used binomial distribution to determine the minimal number of positive samples, and the probability of detecting the required number of positive samples, for different tests, required to assign norovirus as the causative agent of an outbreak of acute gastroenteritis.

RESULTS

For either a standard RT-PCR or a commercially available ELISA, finding only 1 sample positive out of 2, 3 or 4 samples is sufficient to assign norovirus as the causative agent of an outbreak of acute gastroenteritis. However, when ELISA is used, the probability of detecting this required minimum number of positive samples is low when small numbers of samples are tested (57% when 2 samples are tested; 72% when 3 samples are tested). In order to reach a 90% probability of detecting a norovirus outbreak (false negativity at outbreak level <10%), at least 3 samples should be tested using RT-PCR, and 6 samples when using an ELISA.

CONCLUSIONS

The sensitivity for NoV outbreak diagnosis will increase from 57% to 92%, or from 84% to 96%, for ELISA or RT-PCR respectively, when sample size increases from 2 to 6. Thus, using ELISA instead of RT-PCR for the detection of norovirus in stool samples will result in considerable numbers of false negative outbreaks unless a minimum of 6 samples are tested per outbreak.

European multicenter evaluation of commercial enzyme immunoassays for detecting norovirus antigen in fecal samples

A total of 2,254 fecal samples were tested in a European multicenter evaluation of commercially available norovirus antigen detection assays. Two commercial enzyme immunoassays, IDEIA Norovirus (Oxoid; Thermo Fisher Scientific, Ely, United Kingdom) and RIDASCREEN Norovirus (R-Biopharm, Darmstadt, Germany), were included in the evaluation, and their performance was compared with the results of reverse transcription-PCR (RT-PCR). Included in the evaluation were samples collected in sporadic cases of gastroenteritis, samples from outbreaks in which two or more samples were collected, well-characterized samples representing genotypes currently cocirculating within Europe, and samples collected from patients with gastroenteritis caused by a pathogen other than norovirus. The sensitivities and specificities of the IDEIA Norovirus and RIDASCREEN Norovirus assays were 58.93 and 43.81% and 93.91 and 96.37%, respectively, compared with RT-PCR. The sensitivities of both assays for outbreak investigations improved when six or more samples from an outbreak were examined. The IDEIA Norovirus assay exhibited reactivity to a broader range of norovirus genotypes than the RIDASCREEN Norovirus assay, which showed genotype-dependent sensitivities. The results indicate that, if used, these assays should serve as screening assays and the results should be confirmed by RT-PCR.

Evaluation of two commercial enzyme immunoassays for the detection of norovirus in faecal samples from hospitalised children with sporadic acute gastroenteritis

Two commercially available enzyme immunoassays (EIAs), IDEIA and Ridascreen, for norovirus antigen detection were evaluated with 117 faecal samples from hospitalised children with acute gastroenteritis. Eighteen of 39 samples positive by RT-PCR were characterised by sequence analysis, and 17 of these were related to norovirus genogroup II. When compared with RT-PCR, the sensitivity and specificity values were 76.9% and 85.9%, respectively, for the IDEIA assay, and 59.0% and 73.1%, respectively, for the Ridascreen assay. The sensitivity and specificity of both EIA tests require improvement, but they could both eventually be of use in the diagnosis of norovirus diarrhoea in clinical laboratories.

High efficiency cross-reactive monoclonal antibody production by oral immunization with recombinant norwalk virus-like particles

Monoclonal antibodies (MAbs) are important for in-depth antigenic characterization and diagnosis of infections with human caliciviruses that cause almost all outbreaks of nonbacterial gastroenteritis. We compared different routes of immunization with nonreplicating virus-like particles (VLPs) from recombinant Norwalk virus (rNV) and recombinant Mexico virus (rMX) administered to BALB/c mice to determine the efficiency of hybridoma production. Oral immunization with VLPs without adjuvant resulted in high yields of MAb-secreting hybridomas (90%) to these VLPs of IgG (61%), IgM (29%) and IgA (10%) isotypes. Fusions with mesenteric lymph node lymphocytes yielded MAbs of various subclasses including IgG2a, IgG3, IgM and IgA. These results suggest that an immunization route that mimics the natural route of viral infection pathway may facilitate MAb technology by increasing the yields of antibody secreting hybridoma cells.

Comparison of the RIDASCREEN norovirus enzyme immunoassay to IDEIA NLV GI/GII by testing stools also assayed by RT-PCR and electron microscopy

RIDASCREEN norovirus enzyme immunoassay (EIA) detected 80.3% of norovirus-infected feces samples compared to 60.6% by IDEIA NLV GI/GII from 228 patients with no false positives by either assay. RT-PCR and electron microscopy percent sensitivity and specificity were 98.5, 100 and 36.4 and 96.9, respectively.

Gastroenteric Viruses

In recent years, viruses have been recognized increasingly as an important cause of foodborne infections. More than 160 enteric viruses are excreted in the feces of infected individuals, and some may also be present in the vomitus. Food and water are directly contaminated with fecal material, through the use of sewage sludge in agriculture, sewage pollution of shellfish culture beds, or may be contaminated by infected food-handlers.

Viral gastroenteritis in children hospitalised in Sicily, Italy

The aim of the present study was to describe the epidemiologic and clinical characteristics of acute viral gastroenteritis in hospitalised Italian children. A total of 215 stool specimens were collected from January to December 2003 from patients hospitalised in Palermo for acute diarrhoea. Samples were tested for group A rotavirus, astrovirus, adenovirus, norovirus, enteropathogenic bacteria, and parasites. Rotaviruses, mostly belonging to types G1-G4, were detected in 25.1% of samples, astrovirus in 7%, adenovirus in 6%, norovirus in 18.6%, and bacterial agents in 17.2%. No parasitic infections were diagnosed. Mixed infections represented 9.8% of all cases. The mean and median ages of children with rotavirus gastroenteritis were lower than those of children with other viruses (p = 0.029), with the highest median ages being found in astrovirus-infected patients. Vomiting and dehydration were more frequent among patients with viral infection (p < 0.01), and the severity score was significantly higher for children infected with astrovirus or group A rotavirus (p = 0.008). Rotavirus was the leading cause of prolonged hospitalisation (p = 0.005). In conclusion, viruses were confirmed in Italy as the most common cause of severe enteric illness in childhood, with rotavirus types G1-G4, which correspond to those included in the rotavirus vaccines being developed, playing the main role. Routine testing should be introduced for noroviruses, since they seem to represent an important cause of sporadic paediatric gastroenteritis.

Enhanced reverse transcription-PCR assay for detection of norovirus genogroup I

We have developed a one-tube reverse transcription (RT)-PCR method using the real-time TaqMan PCR system for the detection of norovirus genogroup I (NV GGI). By introduction of a novel probe based on locked nucleic acid technology, we enhanced the sensitivity of the assay compared to those of conventional TaqMan probes. The sensitivity of the NV GGI RT-PCR was determined by probit analysis with defined RNA standards and quantified norovirus isolates to 711 copies/ml (95% detection limit). In order to detect PCR inhibition, we included a heterologous internal control (IC) system based on phage MS2. This internally controlled RT-PCR was tested on different real-time PCR platforms, LightCycler, Rotorgene, Mastercycler EP realplex, and ABI Prism. Compared to the assay without an IC, the duplex RT-PCR exhibited no reduction in sensitivity in clinical samples. In combination with an established NV GGII real-time RT-PCR, we used the novel assay in a routine assay for diagnosis of clinical and food-borne norovirus infection. We applied this novel assay to analyze outbreaks of nonbacterial acute gastroenteritis. Norovirus of GGI was detected in these outbreaks. Sequence and similarity plot analysis of open reading frame 1 (ORF1) and ORF2 showed two genotypes, GGI/2 and GGI/4, in semiclosed communities.

Diagnosis of Norovirus outbreaks by commercial ELISA or RT-PCR

The IDEIA Norwalk-like virus (Dakocytomation Ltd., Ely, United Kingdom) and the Ridascreen Norwalk-like virus enzyme immunoassay (R-Biopharm AG, Darmstadt, Germany), were evaluated for the diagnosis of outbreaks of acute gastroenteritis. A panel of 158 fecal samples from 23 outbreaks, including confirmed rotavirus and astrovirus outbreaks, was used to determine the sensitivity and specificity of both ELISA kits relative to an RT-PCR protocol that was followed by Southern blot hybridization. Another panel consisted of 6 different genogroup I strains, 12 genogroup II strains and 1 genogroup IV strain and was used to determine the scope of the tests. Compared to the RT-PCR, sensitivities of 38% and 36% and specificities of 96% and 88% were found for the Dako kit and the Ridascreen kit, respectively. Two genogroup I strains, and one genogroup II strain were not detected by the Dako kit, while five genogroup I and five genogroup II strains were not detected by the Ridascreen kit. The sensitivity of both ELISA kits, and the scope of the Ridascreen are considered disappointing. However, the ELISA kits can be useful for a preliminary screening, provided that ELISA negative outbreaks will be re-tested by RT-PCR methods.

Evaluación de dos métodos de detección antigénica por ELISA para el diagnóstico de brotes causados por norovirus

INTRODUCTION

The aim of this study was to assess two ELISA techniques for the detection of outbreaks of norovirus.

METHOD

One-hundred and sixty-five fecal samples from patients affected in 30 outbreaks were studied.

RESULTS

On the basis of a specific consensus criterion between techniques for confirming outbreaks, the sensitivity and specificity was respectively 80% and 90% for RIDASCREEN, and 80% and 100% for IDEIA.

CONCLUSION

These techniques could be useful for rapid detection of norovirus outbreaks in laboratories that lack molecular confirmation techniques.

Real-time reverse transcription-PCR for detection of rotavirus and adenovirus as causative agents of acute viral gastroenteritis in children

Viral pathogens are the most common cause of gastroenteritis in developed countries. Human rotavirus and adenovirus infections are major causes of acute outbreaks and sporadic cases of gastroenteritis, occurring primarily among children less than 2 years of age. Patient hospitalization is often required, with enormous infection control implications. This work describes the development of real-time PCR assays for the detection of group F adenovirus, rotavirus A, and rotavirus C from stool specimens. Two hundred twenty stool samples from pediatric patients exhibiting symptoms of diarrhea and/or vomiting were examined. PCR results were compared with those of virus detection by electron microscopy and latex agglutination antigen detection. The incorporation of an internal-control RNA that was spiked into individual stool extracts functioned as an internal validation for the reporting of PCR-negative results. Rotavirus C was not detected by real-time PCR in the patient stool samples examined. Real-time reverse transcription-PCR resulted in 175% and 111% increases in the rates of detection of adenovirus F and rotavirus A, respectively, compared with latex agglutination testing. Molecular detection increased the number of stool specimens in which causative agents of gastroenteritis were identified by 155% compared to electron microscopy. Genotyping of a proportion of the rotavirus and adenovirus strains identified only genotype G1 rotavirus and both adenovirus genotypes 40 and 41 in circulation within the patient cohort examined. The results highlight the significance of rapid molecular methods for the routine screening of stool samples in hospital laboratories to provide rapid definitive diagnoses.

Detection of norovirus antigens from recombinant virus-like particles and stool samples by a commercial norovirus enzyme-linked immunosorbent assay kit

The commercial norovirus enzyme-linked immunosorbent assay kit was evaluated for its reactivity to recombinant virus-like particles and the detection of natural viruses from stool samples of Japanese infants and children with sporadic acute gastroenteritis compared to reverse transcription-PCR. The kit had a sensitivity of 76.3% and a specificity of 94.9%. Our results clearly indicated that the kit allows the detection of the most prevalent genotype, GII/4. In order to increase the sensitivity of the kit, the reactivity with norovirus of GII/3 and GII/6 genotypes needs to be improved.

Evaluation of a commercial enzyme immunoassay for the detection of norovirus antigen in fecal samples from children with sporadic acute gastroenteritis

The Ridascreen Norwalk-like virus enzyme immunoassay was compared with (RT)-PCR on 92 stool samples collected from children with sporadic acute gastroenteritis. Homogenization and pre-dilution of the whole stool sample resulted in high specificity (97.5%) and moderate sensitivity (60%). This assay may be useful to screen outbreaks for norovirus, but limited to detect the virus in sporadic cases of diarrhea.

Evaluation of the Dako IDEIA norovirus EIA assay for detection of norovirus using faecal specimens from Australian gastroenteritis outbreaks

AIMS

New techniques for detection of norovirus, a major cause of gastroenteritis, require ongoing evaluation. The aim of this study was to use material from gastroenteritis outbreaks in Victoria, Australia, to evaluate the sensitivity and specificity of the Dako IDEIA norovirus EIA assay, using both photometric and visual analysis.

METHODS

A total of 130 faecal specimens from 41 gastroenteritis outbreaks were tested for norovirus by electron microscopy (EM), a two-round multiplex reverse transcription-polymerase chain reaction (RT-PCR) method and the IDEIA norovirus assay. All specimens with sufficient amplified product were sequenced to determine their norovirus genotype. In addition, six well-established RT-PCR protocols were used to test four EIA-positive, multiplex RT-PCR/EM-negative specimens. Also, a range of RT-PCR protocols was used to test a specimen positive for GII only by the multiplex RT-PCR but positive for GI and GII by the EIA. The effect of multiple freezing-thawing cycles on EIA positivity was tested on seven additional specimens. A further seven specimens, known to contain the gastroenteritis viruses sapovirus, adenovirus, astrovirus and rotavirus were also tested by the IDEIA norovirus assay.

RESULTS

The IDEIA norovirus assay gave a single-specimen sensitivity and specificity of 66% and 85%, respectively (visual analysis compared with the multiplex RT-PCR), 63% and 88% (photometric analysis compared with the multiplex RT-PCR), 65% and 87% (visual analysis compared with the multiplex RT-PCR and/or EM) and 62% and 90% (photometric analysis compared with the multiplex RT-PCR and/or EM). None of the four EIA-positive specimens negative by the multiplex RT-PCR and/or EM was positive by any of the six alternative RT-PCR protocols. The specimen positive for GI and GII by EIA but for GII only by the multiplex RT-PCR was not positive for GI by any of the alternative RT-PCR protocols. A minimum of three specimens per outbreak had to be tested by the EIA to ensure that norovirus-positive outbreaks (multiplex RT-PCR and/or EM) were classified as positive for norovirus by the IDEIA norovirus assay (visual or photometric analysis). However, one specimen from a norovirus-negative outbreak (multiplex RT-PCR and/or EM) for which four specimens were provided was positive for norovirus by the IDEIA norovirus assay. Seven norovirus genotypes were identified by open reading frame 1 sequencing analysis and specimens from all seven norovirus genotypes (as well as an EM-positive/multiplex RT-PCR-negative specimen) were detected by the IDEIA norovirus assay by both visual and photometric analysis. Repeated freezing-thawing cycles (up to six) for faecal specimens did not reduce the sensitivity of the EIA assay but could render an EIA-negative specimen EIA-positive. The specimens positive for sapovirus, adenovirus, astrovirus and rotavirus were EIA-negative.

CONCLUSIONS

The IDEIA norovirus assay lacks the sensitivity and specificity to ascribe a particular result to a particular specimen, but could be useful for detecting norovirus in a gastroenteritis outbreak where specimens are plentiful, although it is difficult to avoid a risk of false positives. Since visual analysis can be used for result assessment almost as reliably as photometric analysis, the test kit would be useful for laboratories lacking specialist equipment such as a photometric microplate reader.

The epidemiologic and clinical importance of norovirus infection

Noroviruses are a major cause of sporadic cases and epidemic outbreaks of gastroenteritis. The development of molecular diagnostic assays has led to an increased recognition of the significance of these viruses as causes of gastroenteritis in all age groups. This article reviews the epidemiology, clinical manifestations and pathogenesis of norovirus infection, and it describes the diagnostic and therapeutic approaches to this disease.

[Norovirus infections in Germany]

Noroviruses are responsible for the majority of acute viral gastroenteritis infections worldwide. Transmission may be faecal-oral or through contaminated food and water or airborne by virus-containing aerosols. Characteristics of noroviruses that facilitate their spread are their high concentration in stool and vomitus, their extreme environmental stability, their low infectious dose as well as the lack of long-lasting immunity. The majority of norovirus infections occur in large outbreaks among persons living in institutional settings, such as hospitals and nursing homes, although sporadic cases also occur. Children and elderly persons are most often affected. Illness is characterized by acute onset of projectile vomiting. For prevention and control of norovirus outbreaks strict control management is necessary. Based on the high genomic variability new variant noroviruses with different pathogenic factors can arise. Depending on the circulating variant the extent of the usual winter peak can vary enormously. Available diagnostic methods include RT-PCR assays for detection of viral RNA, electron microscopy and enzyme immunoassays (EIA) for detection of viral antigens. The implicated virus can be subtyped through nucleotide sequencing and linked to a specific outbreak. With the enactment of the Protection against Infection Act in January 2001 a mandatory reporting system of norovirus infections was established. Analysis of surveillance data from this system permits a detailed overview of the nationwide epidemiology of this disease in Germany.

Emergence of a new norovirus genotype II.4 variant associated with global outbreaks of gastroenteritis

Norovirus (NoV) is highly infectious and is the major cause of outbreak gastroenteritis in adults, with pandemic spread of the virus being reported in 1995 and 2002. The NoV genome is genetically diverse, which has hampered development of sensitive molecular biology-based methods. In this study we report on a nested reverse transcriptase PCR (nRT-PCR) that was designed to amplify the highly conserved 3' end of the polymerase region and the 5' end of the capsid gene of NoV genogroup II (GII). The nRT-PCR was validated with strains isolated from sporadic and outbreak cases between 1997 and 2004 in New South Wales, Australia. Phylogenetic analysis identified six genotypes circulating in New South Wales, GII.1, GII.3, GII.4, GII.6, GII.7, and GII.10, with GII.4 being the predominant genotype. In 2004, there was a marked increase in NoV GII activity in Australia, with a novel GII.4 variant being identified as the etiological agent in 18 outbreaks investigated. This novel GII.4 variant, termed Hunter virus, differed by more than 5% at the amino acid level across the capsid from any other NoV strain in the GenBank and EMBL databases. The Hunter virus was subsequently identified as the etiological agent in large epidemics of gastroenteritis in The Netherlands, Japan, and Taiwan in 2004 and 2005.