Foodborne viruses

Quantitative detection of norovirus excretion in pediatric patients with cancer and prolonged gastroenteritis and shedding of norovirus

Although chronic courses of norovirus infection have been described in immunocompromised patients, little is known about noroviral shedding and correlation with clinical symptoms in these patients. In this report, the quantitative courses of norovirus excretion in nine pediatric patients with hematologic and oncologic disorders and prolonged gastroenteritis were investigated. In a retrospective study multiple fecal samples from nine pediatric cancer patients were examined by a one-step real-time PCR. Clinical data of the patients were reviewed and virological data were correlated with clinical symptoms. All nine patients presented with prolonged illness and prolonged noroviral shedding. Vomiting and diarrhea were associated with high norovirus concentrations and norovirus excretion declined slowly in the patients. Retrospectively, initial PCR-testing for norovirus was performed with a median of 7 days after onset of symptoms. This finding hints at the difficulty of obtaining early diagnosis of the infection in these children. The patients were shedding high norovirus concentration over a long period of time. Results of sequential quantitative PCR-testing for norovirus correlated with clinical symptoms. Both clinical symptoms and quantitative PCR-testings help to define the severity of norovirus infection and to estimate the risk for transmission. To prevent the spread of the disease, usage of virocidal disinfectants and isolation procedures should be maintained as long as patients are positive for noroviruses. Since vomiting is frequent in pediatric patients with oncological conditions, a screening program for rapid detection of norovirus infection in this group of patients should be considered.

Detection of a novel intergenogroup recombinant Norovirus from Kolkata, India

Mutation and recombination are recognized as important driving forces of evolution among RNA viruses. An intergenogroup recombinant norovirus strain [Hu/Kol/NLV/L8775/AB290150/2006/India] was detected in the faecal specimen of a 17 year old male, who had suffered from acute watery diarrhea and severe dehydration. Sequence analysis confirmed that this novel recombinant strain had a polymerase gene fragment that closely resembled a Norovirus (NoV) genogroup-I genotype-3 virus (HuCV/NLV/GI.3/VA98115/AY038598/1998/USA) and a capsid gene resembling NoV genogroup-II genotype-4 virus (NoV/Hu/GII.4/Terneuzen70/EF126964/2006/NL). The crossing over and recombination was observed at nucleotide (nt) 790 of NoV GI VA98115 strain and nt808 of NoV GII Terneuzen70 strain. In both parent strains conserved nucleotide sequence and hairpin structure (DNA secondary structure) were reported at the junction point of ORF1 and ORF2, exhibiting the mechanism of recombination in these viruses. Thus this novel recombinant NoV is another step in evolution among NoVs, indicating that constant surveillance is important to successfully monitor emergence of these strains.

Development of a DNA microarray for the simultaneous detection and genotyping of noroviruses

Current methods for detecting and genotyping noroviruses focus on the use of reverse transcriptase (RT)-mediated PCR. A major drawback of this approach is that short target RT-PCR products do not always encompass sequences that can be compared among research laboratories, resulting in difficulties for molecular epidemiology. We describe the use of a microarray-based system for simultaneous detection and molecular characterization of noroviruses. The protocol generates a 917-bp RT-PCR product that encompasses two major regions currently used for detection and analysis of norovirus genomes. The PCR products are then hybridized to an oligonucleotide array (NoroChip) based on 50-mer features, which allows for both confirmation of reaction specificity and molecular characterization of the amplified genome. Parallel sequence analyses of amplicons revealed that our microarray data were robust in separating genogroups I and II, and further subtyping to the cluster level was possible. This approach, combining detection and characterization, overcomes the need for expensive and time-consuming sequence analysis of amplified genome targets for molecular epidemiology.

Detection and quantification of group C rotaviruses in communal sewage

Group C rotaviruses have been recognized as a cause of acute gastroenteritis in humans, cattle, and swine, although the true epidemiologic and clinical importance of this virus in these hosts has not yet been fully established. A real-time PCR assay based on a broadly reactive primer pair was developed and used to quantitatively determine the viral load of group C rotaviruses in environmental samples. A total of 35 raw and 35 treated sewage samples collected at the same sampling time in four Hungarian sewage treatment plants during a survey in 2005 were tested for the presence of group C rotaviruses. The overall detection rates were 91% (32 of 35) for the influent and 57% (20 of 35) for the effluent samples. Molecular characterization of the amplified partial VP6 gene revealed the cocirculation of human and animal (i.e., bovine and porcine) strains that were easily distinguishable by melting curve analysis. Human strains yielded relatively high viral loads (mean, 1.2 x 10(7); median, 6.9 x 10(5) genome equivalents per liter influent sewage) and appeared to display seasonal activity over the study period, whereas animal strains appeared to circulate throughout the year at much lower average titers (bovine strains mean, 9.9 x 10(4); median, 3.0 x 10(4); porcine strains mean, 3.9 x 10(4); median, 3.1 x 10(4) genome equivalents per liter influent sewage). Our findings suggest that monitoring of communal sewage may provide a good surrogate for investigating the epidemiology and ecology of group C rotaviruses in humans and animals.

Genetic relatedness of noroviruses identified in sporadic gastroenteritis in children and gastroenteritis outbreaks in northern Alberta

We compared the proportion and genotype distribution of norovirus (NoV) identified in sporadic acute gastroenteritis in children younger than 7 years old with the NoV strains found in outbreaks from January 2003 through April 2004 in northern Alberta, Canada. Eight genogroup I (GI) and 133 GII NoV cases were detected in 1,166 cases of acute sporadic childhood gastroenteritis with a monthly detection rates varying from 6.0% to 20.4% and no sporadic gastroenteritis case in October 2003. Seventy-eight outbreaks (65%) tested positive for NoV during the study period with an obvious winter predominance and no NoV outbreaks in August, September, and October 2003. Three GI and 51 GII strains from the sporadic childhood gastroenteritis cases and seven GI and 37 GII strains from gastroenteritis outbreaks were sequenced and analyzed. Strains belonging to the GII.4 cluster predominated in outbreaks (68%) while the strains in sporadic childhood gastroenteritis demonstrated significant heterogeneity with the majority belonging to the GII.3 cluster (36%). Further analysis of NoV strains from 34 sporadic childhood gastroenteritis cases and 38 gastroenteritis outbreaks in chronologically and geographically related groups failed to demonstrate clear link between strains circulating in the setting of sporadic childhood gastroenteritis and those found in outbreaks.

Phylogenetic analysis of norovirus isolates involved in some Canadian gastroenteritis outbreaks in 2004 and 2005

Noroviruses are recognized as the most common cause of nonbacterial gastroenteritis worldwide. In this study, we investigated the molecular epidemiology of noroviral isolates in Canada from 2004 to 2005 by sequencing the RNA polymerase gene and capsid N-terminal/shell (N/S) domain. Norovirus genogroups I and II were thus found to have co-circulated in Canada during the studied period, with a higher incidence of genogroup II (95.7%). The GII-4 or Lordsdale subgroup was the predominant genotype, suggesting that norovirus genogroup II is the major cause of viral gastroenteritis in Canada, as it is in many other countries. Phylogenetic analyses of the RNA polymerase gene and the capsid N/S domain indicated different genotypes for 2 strains, suggesting probable genetic recombination. Sequencing of the norovirus polymerase gene may reflect actual classification but should be supported by sequence information obtained from the capsid gene.

Evaluation of an extracting method for the detection of Hepatitis A virus in shellfish by SYBR-Green real-time RT-PCR

Consumption of virus-contaminated shellfish has caused numerous outbreaks of gastroenteritis and hepatitis worldwide. In the present study, we evaluated a rapid and simple extraction method to concentrate and purify enteric viruses from shellfish tissues for their detection by real-time RT-PCR. This procedure consists of an alkaline elution with a glycine buffer, solids removal by slow speed centrifugation, purification by chloroform extraction and virus concentration by ultracentrifugation. The efficiency of this method to recover Hepatitis A virus (HAV) from oysters seeded with this virus, was assessed by real-time RT-PCR and conventional RT-nested PCR after extracting viral RNA by a commercial isolation kit. Real-time RT-PCR yielded higher detection sensitivity than the obtained by conventional RT-nested PCR. Besides the improvements in detection sensitivity, the real-time RT-PCR, by quantifying HAV RNA, allowed to check the overall extraction procedure and the recovery efficiency after each processing step. After the last phase, i.e. virus concentration by ultracentrifugation, the RNA purity was high but the estimated HAV recovery efficiency was however low, probably due to virus losses and the presence of RT-PCR inhibitors in sample concentrates. In contrast, the HAV recovery percentage was higher after the virus elution step while the RNA purity was lower. Real-time RT-PCR detection could allow to eliminate some purification and concentration steps that are required for conventional RT-nested PCR detection. The overall procedure for detecting HAV could be then simplify avoiding virus losses during manipulation.

Cytokine and antibody responses in gnotobiotic pigs after infection with human norovirus genogroup II.4 (HS66 strain)

A human norovirus genogroup II.4 strain HS66 (HuNoV-HS66) infects and causes mild diarrhea in gnotobiotic (Gn) pigs (S. Cheetham, M. Souza, T. Meulia, S. Grimes, M. G. Han, and L. J. Saif, J. Virol. 80:10372-10381, 2006). In this study we evaluated systemic and intestinal humoral and cellular immune responses to HuNoV-HS66 in orally inoculated pigs. Antibodies and type I interferon (IFN-I or IFN-alpha), proinflammatory interleukin-6 (IL-6), Th1 (IL-12 and IFN-gamma), Th2 (IL-4), and Th2/regulatory T ([T(reg)] IL-10) cytokine profiles in serum and intestinal contents (IC) of the HuNoV-HS66-inoculated pigs and controls were assessed by enzyme-linked immunosorbent assay at selected postinoculation days (0 to 28). Using an enzyme-linked immunospot assay, we evaluated immunoglobulin M (IgM), IgA, and IgG antibody-secreting cells (ASC) and cytokine-secreting cells (CSC) in intestine, spleen, and blood. In the HuNoV-inoculated pigs, antibody titers in serum and IC were generally low, and 65% seroconverted. Pigs with higher diarrhea scores were more likely to seroconvert and developed higher intestinal IgA and IgG antibody titers. The numbers of IgA and IgG ASC were higher systemically than in the gut. In serum, HuNoV induced persistently higher Th1 (low transient IFN-gamma and high IL-12) than the other cytokines, but also low Th2 (IL-4) and Th2/T(reg) (IL-10) levels; low, transient proinflammatory (IL-6) cytokines; and, notably, a delayed IFN-alpha response. In contrast, intestinal innate (IFN-alpha early and late) and Th1 (IL-12 late) cytokines were significantly elevated postinfection. HuNoV-HS66 also elicited higher numbers of Th1 (IL-12 and IFN-gamma) CSC than Th2 (IL-4) and proinflammatory (IL-6) CSC, with the latter responses low in blood and intestine, reflecting low intestinal inflammation in the absence of gut lesions. These data provide insights into the kinetics of cytokine secretion in serum and IC of HuNoV-inoculated Gn pigs and new information on intestinal humoral and cellular immune responses to HuNoV that are difficult to assess in human volunteers.

[Hepatitis A outbreak in Transdanubia (Hungary): molecular connections and epidemiological conclusions - 2006]

INTRODUCTION

Hepatitis A virus (HAV) is one of the most important cause of fecally transmitted acute infectious hepatitis worldwide. In Hungary, beside the sporadic HAV infections, outbreaks also occur, particularly in Northeast part of the country where the subgenotype IA is endemic. The reported number of HAV cases was less than 10 per year in Southwest Hungary.

AIMS

A part of the European HAV surveillance, the author's aims were to follow and to analyze the outbreak of hepatitis A in Transdanubia (Southwest Hungary) in 2006 by molecular epidemiological methods.

MATERIALS AND METHODS

Sera samples from symptomatic patients were tested prospectively by enzyme-immunoassay (EIA) and reverse transcription-polymerase chain reaction (RT-PCR) followed by sequence- and phylogenetic analysis.

RESULTS

Between June and December 2006, a total of 115 serum samples were positive for HAV IgM antibody in Southwest Hungary. Thirty (76.9%) of the 39 samples were RT-PCR-positive and contain genetically identical subgenotype IB hepatitis A virus (HAV/Transdanubia/2006/HUN) which has 100% nucleotide identity to strain IT-MAR-02 from Italy in 2002. Until now, approximately 1200-1300 persons have been infected with the probably imported strain. The average age of patients was 18 years (years 1 to 80). In this study, detailed clinical and epidemiological data of the outbreak are presented.

CONCLUSIONS

Only a prospective molecular epidemiological study could verify the connection between the first sporadic HAV cases in June, the outbreak in August and the endemic spread of the virus since September in Southwest Hungary. This epidemic calls attention to how a hepatitis A outbreak can develop anywhere and at any time in Hungary and to the importance of active HAV immunization in the primary prevention.

Evaluation of liquid- and fog-based application of Sterilox hypochlorous acid solution for surface inactivation of human norovirus

Noroviruses (NVs) are the most frequent cause of outbreaks of gastroenteritis in common settings, with surface-mediated transfer via contact with fecally contaminated surfaces implicated in exposure. NVs are environmentally stable and persistent and have a low infectious dose. Several disinfectants have been evaluated for efficacy to control viruses on surfaces, but the toxicity and potential damage to treated materials limits their applicability. Sterilox hypochlorous acid (HOCl) solution (HAS) has shown broad-spectrum antimicrobial activity while being suitable for general use. The objectives of this study were to evaluate the efficacy of HAS to reduce NV both in aqueous suspensions and on inanimate carriers. HOCl was further tested as a fog to decontaminate large spaces. HOCl effectiveness was evaluated using nonculturable human NV measured by reverse transcriptase PCR (RT-PCR) and two surrogate viruses, coliphage MS2 and murine NV, that were detected by both infectivity and RT-PCR. Exposing virus-contaminated carriers of ceramic tile (porous) and stainless steel (nonporous) to 20 to 200 ppm of HOCl solution resulted in > or = 99.9% (> or = 3 log10) reductions of both infectivity and RNA titers of tested viruses within 10 min of exposure time. HOCl fogged in a confined space reduced the infectivity and RNA titers of NV, murine NV, and MS2 on these carriers by at least 99.9% (3 log10), regardless of carrier location and orientation. We conclude that HOCl solution as a liquid or fog is likely to be effective in disinfecting common settings to reduce NV exposures and thereby control virus spread via fomites.

Effectiveness of an RT-booster-PCR method for detection of noroviruses in stools collected after an outbreak of gastroenteritis

Noroviruses exhibit a wide genomic and antigenic diversity, making laboratory diagnosis difficult. The abrupt onset of the illness does often not allow timely sample collection. Three different methods (a commercially available ELISA, a published RT-PCR and an RT-booster-PCR) were compared for detecting noroviruses in stools collected after the end of a gastroenteritis outbreak. Both ELISA and the RT-PCR detected noroviruses in 6 samples out of the 41 samples collected and tested. The RT-booster-PCR, however, was able to detect noroviruses in 23 (56%) of the samples with 20 of the samples confirmed by sequencing. Confirmation of PCR products was also undertaken by Southern hybridisation with controversial results (e.g. lack of confirmation on samples positive by sequencing). The results show that common molecular diagnostic methods may fail sometimes to detect the presence of noroviruses in a relevant proportion of samples. A sensitive detection method, such as the RT-booster-PCR described below may resolve the cases.

Waterborne norovirus outbreaks

Noroviruses (NoVs) are the most common nonbacterial causative agents of waterborne outbreaks. Due to the mild and short-lived disease of gastroenteritis, even large epidemics may go unnoticed, since patients do not necessarily visit a doctor. NoVs have several means by which to survive both in the environment and in a population. The nonenveloped small virus retains its infectivity in the environment, and particularly in cold water, for a long time. Unlike most enteric viruses, it causes disease both in children and adults. A large number of genotypes combined with a small infective dose and short-term immunity guarantee efficient circulation of these viruses. The world of NoVs has been revealed to us predominantly by molecular methods. Having learned to detect these viruses first in patients, the emphasis is now in searching for methods sensitive enough to find them in environmental samples. In this review, the latest methods and their use in monitoring of these viruses are discussed.

Comparative evaluation of new TaqMan real-time assays for the detection of hepatitis A virus

Three novel real-time TaqMan RT-PCR assays targeting the 5'-UTR, the viral protease and the viral polymerase regions of the hepatitis A virus (HAV) were developed, evaluated and compared against a new published 5'-UTR TaqMan assay (JN) and a widely used conventional RT-PCR assay (HAVc). All conventional RT-PCR (HAV, SH-Prot and SH-Poly systems) and TaqMan (SH-Prot, SH-Poly, JN and SH-5U systems) assays evaluated were consistent for the detection of the three different HAV strains (HM-175, HAS-15 and LSH/S) used and reproducible for both RNA duplicates with the exception of two reproducibility discrepancies observed with both 5'-UTR real-time systems (JN and SH-5U). Limits of detection for conventional HAV, SH-Prot and SH-Poly RT-PCR systems were found to be equivalent when tested with serially diluted suspensions of the HM-175 strain. Although the four real-time RT-PCR TaqMan assays evaluated herein produced similar and consistent quantification data down to the level of one genomic equivalent copy with their respectively cloned amplicons, significant and important differences were observed for the detection of HAV genomic RNA. Results showed that the new real-time TaqMan SH-Poly and SH-Prot primer and probe systems were more consistent and sensitive by 5 logs as compared to both 5'-UTR designs (JN and SH-5U) used for the detection of HAV genomic RNA as well as for the detection in cell culture by cytopathic effect. Considering their higher analytical sensitivity, the proposed SH-Poly and SH-Prot amplification systems could therefore represent valuable tools for the detection of HAV in clinical, environmental and food samples.

Molecular epidemiology of norovirus outbreaks in Norway during 2000 to 2005 and comparison of four norovirus real-time reverse transcriptase PCR assays

During the period from January 2000 to August 2005 a total of 204 outbreaks of norovirus gastroenteritis were diagnosed at the Norwegian Institute of Public Health. A clear increase in the norovirus activity was seen in healthcare institutions during the winter seasons. Polymerase sequence analysis of norovirus strains from 122 outbreaks showed that 112 were caused by GII strains (91.8%). Two norovirus variants seen during the study period-GIIb and GII.4-were predominant between January 2000 and September 2002, whereas GII.4 was predominant from September 2002 onward. The highest norovirus activity was seen during the 2002-2003 and 2004-2005 seasons with the emergence of new GII.4 variants. This study describes the molecular epidemiology of norovirus strains circulating in Norway during the five previous seasons and compares four norovirus real-time reverse transcriptase PCR assays. A suitable assay for routine diagnostics is suggested.

Detection of calicivirus from fecal samples from children with acute gastroenteritis in the West Central region of Brazil

The objective of this study was to describe the circulation of caliciviruses in the West Central region of Brazil and its correlation with children's gender and age, as well as with the year and months of the sample collection. Reverse transcriptase-polymerase chain reaction was performed to detect the human calicivirus genome in 1006 fecal samples that were collected in Goiânia (n = 696) and Brasília (n = 310). Viral RNA was detected in 8.6% of the samples. No significant difference in viral prevalence was found regarding gender, age or year of the sample. However, it was observed that in Goiânia, there is a higher incidence of caliciviruses from September to March. The analysis employing three primer pairs demonstrated that the Ni/E3 or JV12/13 primer pairs, which detect norovirus (NoV), detected 41 positive samples while the 289/290 primer pair, which detects NoV or sapovirus, detected the remaining 46 samples. Calicivirus circulates in the West Central region of Brazil and for better detection of this virus it is important to use more than one primer pair. Also, we conclude that the seasonality presented by this virus is related to higher humidity in the period.

Inactivation of poliovirus 1 and F-specific RNA phages and degradation of their genomes by UV irradiation at 254 nanometers

Several models (animal caliciviruses, poliovirus 1 [PV1], and F-specific RNA bacteriophages) are usually used to predict inactivation of nonculturable viruses. For the same UV fluence, viral inactivation observed in the literature varies from 0 to 5 logs according to the models and the methods (infectivity versus molecular biology). The lack of knowledge concerning the mechanisms of inactivation due to UV prevents us from selecting the best model. In this context, determining if viral genome degradation may explain the loss of infectivity under UV radiation becomes essential. Thus, four virus models (PV1 and three F-specific RNA phages: MS2, GA, and Qbeta) were exposed to UV radiation from 0 to 150 mJ.cm-2. PV1 is the least-resistant virus, while MS2 and GA phages are the most resistant, with phage Qbeta having an intermediate sensitivity; respectively, 6-log, 2.3-log, 2.5-log, and 4-log decreases for 50 mJ.cm-2. In parallel, analysis of RNA degradation demonstrated that this phenomenon depends on the fragment size for PV1 as well as for MS2. Long fragments (above 2,000 bases) for PV1 and MS2 fell rapidly to the background level (>1.3-log decrease) for 20 mJ.cm-2 and 60 mJ.cm-2, respectively. Nevertheless, the size of the viral RNA is not the only factor affecting UV-induced RNA degradation, since viral RNA was more rapidly degraded in PV1 than in the MS2 phage with a similar size. Finally, extrapolation of inactivation and UV-induced RNA degradation kinetics highlights that genome degradation could fully explain UV-induced viral inactivation.

Molecular epidemiology of group A rotaviruses in water sources and selected raw vegetables in southern Africa

Group A rotaviruses (RVs) are the most important cause of acute viral gastroenteritis in infants and young children. In this study raw and treated drinking water supplies at plants in two geographic areas, as well as selected irrigation water and corresponding raw vegetables in three regions of southern Africa, were screened for the presence of RVs using molecular techniques. Group A RVs were detected in 11.8% of partially treated and 1.7% of finally treated drinking water samples and in 14% of irrigation water samples and 1.7% of corresponding raw vegetable samples. Type-specific reverse transcriptase-PCR and sequence analysis revealed the presence of multiple types (G1, G2, G8, and G9) in irrigation water and single types (G1 or G3) in raw and treated drinking water. Group A RVs detected in all samples consisted of mixed P types (P[4], P[6], P[8], and P[9]), with P[6] predominating. The detection of types G8, G9, and P[6] reflects the emergence of these types in clinical infections. The similarity of environmental types to those in patients with clinical RV infections confirms the value of wastewater screening as a tool for assessing RVs circulating in communities, with the benefit of detecting types that cause both clinical and subclinical infections. The results provide new information on RV types in water and related environments and identify the potential risk of waterborne transmission. In addition, the presence of RVs in drinking water underlines shortcomings in quality specifications. These data provide valuable information regarding the prevalence of RVs in environmental sources, with important implications for vaccine development.

Comparative evaluation of RT-PCR, nucleic acid sequence-based amplification (NASBA) and real-time RT-PCR for detection of noroviruses in faecal material

Using different primer and probe sets, RT-PCR, NASBA and TaqMan RT-PCR molecular methods were compared to detect NoV GII in 13 clinical stool samples. The RT-PCR results observed by gel electrophoresis (Ando, Kageyama and Anderson amplification and probe systems), dot blot hybridization (Ando and Kageyama) and real-time TaqMan assay (Ando and Kageyama) were shown to be consistent and reproducible for the detection of NoV GII. Whereas, the NASBA assay using Ando primers showed some reproducibility discrepancies. Detection limits of the NoV GII/Kageyama system were found to be equal or significantly higher than the Ando system. Real-time TaqMan RT-PCR assay showed similar detection limits to that of NASBA with the Kageyama amplification and detection system, while it was 1log less sensitive than the Ando system. In a clinical context, RT-PCR, NASBA and real-time TaqMan RT-PCR methods using undiluted samples were all suitable for the detection of NoV GII, however the NASBA assay provided less consistent signals. The NoV GII Kageyama real-time TaqMan RT-PCR assay was reliable with a high analytical sensitivity and has shown the capability of detecting one genomic equivalent copy.

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.

Inactivation of foodborne viruses of significance by high pressure and other processes

The overall safety of a food product is an important component in the mix of considerations for processing, distribution, and sale. With constant commercial demand for superior food products to sustain consumer interest, nonthermal processing technologies have drawn considerable attention for their ability to assist development of new products with improved quality attributes for the marketplace. This review focuses primarily on the nonthermal processing technology high-pressure processing (HPP) and examines current status of its use in the control and elimination of pathogenic human viruses in food products. There is particular emphasis on noroviruses and hepatitis A virus with regard to the consumption of raw oysters, because noroviruses and hepatitis A virus are the two predominant types of viruses that cause foodborne illness. Also, application of HPP to whole-shell oysters carries multiple benefits that increase the popularity of HPP usage for these foods. Viruses have demonstrated a wide range of sensitivities in response to high hydrostatic pressure. Viral inactivation by pressure has not always been predictable based on nomenclature and morphology of the virus. Studies have been complicated in part from the inherent difficulties of working with human infectious viruses. Consequently, continued study of viral inactivation by HPP is warranted.

Diagnosis of hepatitis a virus infection: a molecular approach

Current serologic tests provide the foundation for diagnosis of hepatitis A and hepatitis A virus (HAV) infection. Recent advances in methods to identify and characterize nucleic acid markers of viral infections have provided the foundation for the field of molecular epidemiology and increased our knowledge of the molecular biology and epidemiology of HAV. Although HAV is primarily shed in feces, there is a strong viremic phase during infection which has allowed easy access to virus isolates and the use of molecular markers to determine their genetic relatedness. Molecular epidemiologic studies have provided new information on the types and extent of HAV infection and transmission in the United States. In addition, these new diagnostic methods have provided tools for the rapid detection of food-borne HAV transmission and identification of the potential source of the food contamination.

Risk groups for clinical complications of norovirus infections: an outbreak investigation

Norovirus infections have been described as self-limiting diseases of short duration. An investigation of a norovirus outbreak in a university hospital provided evidence for severe clinical features in patients with several underlying diseases. Clinical outcomes of norovirus infection were defined. Risk-factor analysis targeting underlying diseases and medication was performed using multivariate analyses. In five outbreak wards, 84 patients and 60 nurses were infected (an overall attack rate of 32% in patients, and 76% in nurses). The causative agent was the new variant Grimsby virus. Severe clinical features, including acute renal failure, arrhythmia and signs of acute graft organ rejection in renal transplant patients, were observed in seven (8.3%) patients. In multivariate analyses, cardiovascular disease (OR 17.1, 95% CI 2.17-403) and renal transplant (OR 13.0, 95% CI 1.63-281) were risk-factors for a potassium decrease of >20%. Age >65 years (OR 11.6, 95% CI 1.89-224) was a risk-factor for diarrhoea lasting >2 days. Immunosuppression (OR 5.7, 95% CI 1.78-20.1) was a risk-factor for a creatinine increase of >10%. Norovirus infections in patients with underlying conditions such as cardiovascular disease, renal transplant and immunosuppressive therapy may lead to severe consequences typified by decreased potassium levels, increased levels of C-reactive protein and creatine phosphokinase. In the elderly, norovirus infection may lead to an increased duration of diarrhoea. Therefore patients at risk should be hospitalised early and monitored frequently. Strict preventional measures should be implemented as early as possible to minimise the risk of nosocomial outbreaks.

Detection of hepatitis A virus (HAV) in oysters (Crassostrea gigas)

Because shellfish (oysters, clams, and mussels) are filter-feeders, pathogens become concentrated within them, and human consumption of raw, or under-cooked shellfish can result in disease outbreaks. Identification of hepatitis A virus (HAV) in shellfish has been difficult for several reasons: the concentration of virions in shellfish tissues are very low, detection methods based on in vitro propagation are unreliable, recovery of virions from shellfish tissues is inefficient, and PCR inhibitors in shellfish tissues limit the success of RT-PCR. These facts underlie difficulties in determining cause and effect relationships between hepatitis A outbreaks and detection of HAV contamination in shellfish samples. We have developed a reliable and highly sensitive method for detection of HAV in oyster tissues at low levels (0.001 FFU/ml-fluorescent focus units per milliliter). Our method combines dissection of the gastrointestinal oyster tract, organic extraction before PEG precipitation, and RNA extraction with Trizol LS, followed by RT-PCR and hybridization using a digoxigenin-labeled HAV cDNA probe. Our results will benefit both public health officials concerned about hepatitis A infections caused by consumption of HAV-contaminated oysters and shellfish producers who require reliable methods for quality control of commercial oyster production.

Norovirus outbreaks from drinking water

As part of an intensified monitoring program for foodborne disease outbreaks in Finland, waterborne outbreaks were investigated for viruses. The diagnostic procedure included analysis of patients' stool samples by electron microscopy and reverse transcription-polymerase chain reaction (RT-PCR) for noroviruses and astroviruses. When these test results were positive for a virus, the water sample was analyzed. Virus concentration was based on positively charged filters from 1-L samples. Of the total 41 waterborne outbreaks reported during the observation period (1998-2003), samples from 28 outbreaks were available for analysis. As judged by RT-PCR results from patient samples, noroviruses caused 18 outbreaks. In 10 outbreaks, the water sample also yielded a norovirus. In all but 1 instance, the amplicon sequence was identical to that recovered from the patients. The ubiquity of waterborne norovirus outbreaks calls for measures to monitor water for viruses.

Development of an extraction and concentration procedure and comparison of RT-PCR primer systems for the detection of hepatitis A virus and norovirus GII in green onions

Vegetables can be considered as a vector of transmission for human hepatic and enteric viruses such as hepatitis A virus (HAV) and noroviruses when contaminated by spoiled irrigation water or when prepared by infected food handlers. Recently, outbreaks of HAV have been reported in the USA involving fresh green onions. A viral elution-concentration method was developed for the detection of HAV and norovirus contaminated green onions by RT-PCR. Repeated pipetting/washings of the surface with a pH 9.5 glycine-buffered solution allowed the elution of viruses from the vegetables. Concentration of the viral load was performed by a polyethylene glycol (PEG) precipitation procedure. Viral RNAs were extracted and purified using a combination of Trizol-chloroform and poly(dT) magnetic beads methods. Different sets of primers, including two newly designed primers sets for HAV RT-PCR, were tested in order to achieve the best analytical sensitivity. Using the new primer design, it was possible to detect 10(0) TCID(50%)/25 g of HAV in fresh green onions, while 1 RT-PCRU/25 g was detected for noroviruses GII using previously described primers. This method, based on molecular tools, would be useful for diagnostic laboratories in order to perform viral analyses of such commodities as fresh vegetables in cases of foodborne infections.

Diagnosis of hepatitis a virus infection: a molecular approach

Current serologic tests provide the foundation for diagnosis of hepatitis A and hepatitis A virus (HAV) infection. Recent advances in methods to identify and characterize nucleic acid markers of viral infections have provided the foundation for the field of molecular epidemiology and increased our knowledge of the molecular biology and epidemiology of HAV. Although HAV is primarily shed in feces, there is a strong viremic phase during infection which has allowed easy access to virus isolates and the use of molecular markers to determine their genetic relatedness. Molecular epidemiologic studies have provided new information on the types and extent of HAV infection and transmission in the United States. In addition, these new diagnostic methods have provided tools for the rapid detection of food-borne HAV transmission and identification of the potential source of the food contamination.

Molecular epidemiology of caliciviruses detected in sporadic and outbreak cases of gastroenteritis in France from December 1998 to February 2004

We compiled sequence and epidemiological data from 172 caliciviruses detected in France from December 1998 to February 2004 in sporadic and outbreak cases. The results showed a cocirculation of strains with a majority of genogroup II (GII) noroviruses. Three groups of noroviruses, not detected before in our laboratory, emerged and spread during the period: the recombinant GGIIb and Norwalk-related strains not amplified in the polymerase gene in 2000 and a new Lordsdale variant in 2002. We observed that (i) GII-4 noroviruses were predominant in nursing home and hospital outbreaks but rare in oyster- and water-related outbreaks despite continuous circulation in the population; (ii) at the opposite, genogroup I strains were detected in the majority of environmental outbreaks; (iii) several strains were frequently found in oyster- and water-linked outbreaks (up to seven), whereas one single strain was detected when transmission was from person to person; and (iv) whereas GII noroviruses were predominant in sporadic cases where patients were under 15 years of age, GI strains were more frequent in outbreaks occurring in this age group. Finally, from a methodology point of view, this compilation shows that detection and characterization in the polymerase gene are not adequate in a significant number of cases and should be completed by amplification and sequencing in the capsid gene.

Norovirus recombination in ORF1/ORF2 overlap

Norovirus (NoV) genogroups I and II (GI and GII) are now recognized as the predominant worldwide cause of outbreaks of acute gastroenteritis in humans. Three recombinant NoV GII isolates were identified and characterized, 2 of which are unrelated to any previously published recombinant NoV. Using data from the current study, published sequences, database searches, and molecular techniques, we identified 23 recombinant NoV GII and 1 recombinant NoV GI isolates. Analysis of the genetic relationships among the recombinant NoV GII isolates identified 9 independent recombinant sequences; the other 14 strains were close relatives. Two of the 9 independent recombinant NoV were closely related to other recombinants only in the polymerase region, and in a similar fashion 1 recombinant NoV was closely related to another only in the capsid region. Breakpoint analysis of recombinant NoV showed that recombination occurred in the open reading frame (ORF)1/ORF2 overlap. We provide evidence to support the theory of the role of subgenomic RNA promoters as recombination hotspots and describe a simple mechanism of how recombination might occur in NoV.

Rapid and sensitive detection of noroviruses by using TaqMan-based one-step reverse transcription-PCR assays and application to naturally contaminated shellfish samples

Noroviruses (NoV), which are members of the family Caliciviridae, are the most important cause of outbreaks of acute gastroenteritis worldwide and are commonly found in shellfish grown in polluted waters. In the present study, we developed broadly reactive one-step TaqMan reverse transcription (RT)-PCR assays for the detection of genogroup I (GI) and GII NoV in fecal samples, as well as shellfish samples. The specificity and sensitivity of all steps of the assays were systematically evaluated, and in the final format, the monoplex assays were validated by using RNA extracted from a panel of 84 stool specimens, which included NoV strains representing 19 different genotypes (7 GI, 11 GII, and 1 GIV strains). The assays were further validated with 38 shellfish cDNA extracts previously tested by nested PCR. Comparison with a recently described real-time assay showed that our assay had significantly higher sensitivity and was at least as sensitive as the nested PCR. For stool specimens, a one-step duplex TaqMan RT-PCR assay performed as well as individual genogroup-specific monoplex assays. All other enteric viruses examined were negative, and no cross-reaction between genogroups was observed. These TaqMan RT-PCR assays provide rapid (less than 90 min), sensitive, and reliable detection of NoV and should prove to be useful for routine monitoring of both clinical and shellfish samples.

Adenovirus detection in shellfish and urban sewage in Morocco (Casablanca region) by the polymerase chain reaction

Human enteric viruses are largely excreted in faeces. These resistance of these viruses in the environment makes their faecal-oral transmission easier. Filter feeder organisms such as the mussels are bio-accumulators of viruses contaminating their aquatic environment. Thus, undercooked shellfish consumption involves sanitary risks. Thirty samples of mussels (Mytilus sp.), were tested, half were from an aquaculture origin, the others were from an area more exposed to faecal pollution. Fifteen sewage samples from this last area were also examined. Viruses were extracted from the digestive tissue by direct elution method in a glycine/NaCl pH 9.5 buffer followed by PEG 8000 precipitation. The PEG pellets were used for DNA extraction by proteinase K and phenol/chloroform. The molecular characterization, by PCR using specific adenovirus primers revealed that shellfish growing on Mohammedia (a town in the Casablanca outskirts) littoral are contaminated whereas those chosen from aquaculture and bought in the central market were not contaminated.

Nested multiplex PCR assay for detection of human enteric viruses in shellfish and sewage

Environmental samples and contaminated shellfish present frequently low concentrations of more than one viral species. For this reason, a nested multiplex RT-PCR was developed for the detection of adenoviruses, enteroviruses and hepatitis A viruses in different environmental samples such as urban sewage and shellfish. This assay will save time and cost for detection of these enteric viruses with a smaller sample volume, which otherwise can be a limiting factor in routine analysis. The limit of detection was approximately 1 copy for adenovirus and 10 copies for enterovirus and hepatitis A virus per PCR reaction using titrated cell-cultured viruses as template material. In shellfish and environmental samples, this multiplex PCR was optimized to detect all three viruses simultaneously when the concentration of each virus was equal or lower than 1000 copies per PCR reaction. This is the level found predominantly in the environment and in shellfish when the numbers of fecal bacterial and phage indicators are low. The detection of human adenoviruses by PCR has been suggested as a molecular index of fecal contamination of human origin in the environment and food and the multiplex assay developed may be a tool for evaluating the presence of viral contamination in shellfish and water and to expand microbiological control to include viral markers.

Reverse transcription-booster PCR for detection of noroviruses in shellfish

The methods commonly used for norovirus (NV) detection are based on reverse transcription-PCR (RT-PCR) followed by confirmation of the amplified sequence. To increase sensitivity, an RT-booster PCR was developed. The proposed method showed an increase in sensitivity at least 2 log units for all the NV strains tested compared with the standard RT-PCR method. Higher sensitivity was confirmed in tests on experimentally and naturally contaminated shellfish.

Detection of noroviruses in raspberries associated with a gastroenteritis outbreak

Following an acute foodborne gastroenteritis outbreak in southern Sweden, stool specimens from five of nine ill patients were found positive for norovirus using reverse transcriptase polymerase chain reaction. Epidemiological data pointed to raspberry cakes as the source of the outbreak. Using a combination of generic and patient-specific primers and novel food analysis methodology (with extraction efficiency control and inhibitor removal), norovirus strains from two different genogroups were directly identified in the contaminated raspberries.

Fresh produce: a growing cause of outbreaks of foodborne illness in the United States, 1973 through 1997

Fresh produce is an important part of a healthy diet. During the last three decades, the number of outbreaks caused by foodborne pathogens associated with fresh produce consumption reported to the Centers for Disease Control and Prevention has increased. To identify trends, we analyzed data for 1973 through 1997 from the Foodborne Outbreak Surveillance System. We defined a produce-associated outbreak as the occurrence of two or more cases of the same illness in which epidemiologic investigation implicated the same uncooked fruit, vegetable, salad, or juice. A total of 190 produce-associated outbreaks were reported, associated with 16,058 illnesses, 598 hospitalizations, and eight deaths. Produce-associated outbreaks accounted for an increasing proportion of all reported foodborne outbreaks with a known food item, rising from 0.7% in the 1970s to 6% in the 1990s. Among produce-associated outbreaks, the food items most frequently implicated included salad, lettuce, juice, melon, sprouts, and berries. Among 103 (54%) produce-associated outbreaks with a known pathogen, 62 (60%) were caused by bacterial pathogens, of which 30 (48%) were caused by Salmonella. During the study period, Cyclospora and Escherichia coli O157:H7 were newly recognized as causes of foodborne illness. Foodborne outbreaks associated with fresh produce in the United States have increased in absolute numbers and as a proportion of all reported foodborne outbreaks. Fruit and vegetables are major components of a healthy diet, but eating fresh uncooked produce is not risk free. Further efforts are needed to better understand the complex interactions between microbes and produce and the mechanisms by which contamination occurs from farm to table.

Round-robin comparison of methods for the detection of human enteric viruses in lettuce

Five methods that detect human enteric virus contamination in lettuce were compared. To mimic multiple contaminations as observed after sewage contamination, artificial contamination was with human calicivirus and poliovirus and animal calicivirus strains at different concentrations. Nucleic acid extractions were done at the same time in the same laboratory to reduce assay-to-assay variability. Results showed that the two critical steps are the washing step and removal of inhibitors. The more reliable methods (sensitivity, simplicity, low cost) included an elution/concentration step and a commercial kit. Such development of sensitive methods for viral detection in foods other than shellfish is important to improve food safety.

Modelling effect of physical and chemical parameters on heat inactivation kinetics of hepatitis A virus in a fruit model system

While thermal destruction of pathogenic bacteria has been thoroughly studied in food industry, heat inactivation of viruses in food has been poorly investigated. Experiments were carried out to characterize the effects of controlled physical and chemical characteristics of a food matrix upon heat resistance parameters (D and z values) of hepatitis A virus (HAV), taken as model because of its reported heat resistance. Sucrose content (28-52 degrees Brix), calcium concentration (90-1700 mg kg(-1)) and pH (3.3-4.3) were selected for possible influence on thermal inactivation of HAV in strawberry mashes and thus included in an experimental design according to a Doehlert matrix. Use of this design not only allowed to detect and quantify the direct influence of sucrose concentration upon the D85 degrees C value to be higher than the one of pH, but also to reveal a sucrose concentration/pH specific interaction, while no effect of calcium concentration was evidenced. Although the model cannot be directly used to predict heat resistance in real fruit systems, because of differences observed between predicted and measured D85 degrees C values, it is useful for predicting the trends and relative changes in D values due to sucrose concentration and pH variations. Results suggested possible effects of other constituents of strawberry products on heat resistance of HAV and confirmed the importance of experimental validation of any model-derived process. Nevertheless, such a modelling approach using response surface methodology provides a rapid answer to heat resistance evaluation of a food-borne virus as a function of specific physical and chemical parameters of specific food products.

Comparison of coliforms and coliphages as tools for assessment of viral contamination in river water

The aim of the study was to evaluate the presence of pathogenic viruses in the Moselle River and to compare the usefulness of thermotolerant coliforms and somatic coliphages as tools for river water quality assessment in terms of viral contamination. Thermotolerant coliforms and somatic coliphages were enumerated by standardized methods in 170 samples of river water drawn from five sampling sites along the Moselle River (eastern France). BGM cell culture and integrated cell culture-reverse transcription-PCR DNA enzyme immunoassay were used to determine the presence of pathogenic viral genome (Enterovirus and Norovirus genogroup II [GGII]) and infectious Enterovirus spp. in 90 1-liter samples. No infectious Enterovirus spp. were isolated, but Enterovirus and Norovirus GGII genomes were detected in 38% of the samples. Norovirus GGII genome was mostly detected in winter, whereas Enterovirus genome was mostly detected in summer and fall. Somatic coliphages appeared to be less sensitive to higher river water temperature than thermotolerant coliforms. Furthermore, the number of river water samples positive for pathogenic viral genome increased with increasing concentration of somatic coliphages, whereas coliform concentration was unrelated to viral genome contamination. Consequently somatic coliphages, which are less sensitive to environmental factors than thermotolerant coliforms in river water, would provide a promising tool for assessment of river water quality in terms of fecal and viral pollution.

A simple and rapid single-step multiplex RT-PCR to detect Norovirus, Astrovirus and Adenovirus in clinical stool samples

A single-step multiplex reverse transcription-polymerase chain reaction (RT-PCR) assay that detects and identifies Norovirus, Astrovirus and Adenovirus in clinical stool samples is described. Four hundred sixty stool samples were tested from patients with non-rotavirus acute gastroenteritis, that were either stored at -80 degrees C and tested retrospectively, or tested immediately after viral nucleic acid extraction in a prospective manner, including outbreaks of gastroenteritis that occurred in Germany during the winter of 2003. The multiplex RT-PCR was validated against simplex RT-PCR with published primers for Norovirus (JV12/JV13 and p289/p290) and Astrovirus (Mon340/348), and against simplex PCR for Adenovirus. In both retrospective and prospective settings, the multiplex RT-PCR was equally sensitive and specific in detecting non-rotavirus infections compared with simplex RT-PCR/PCR. The specificity of the multiplex RT-PCR was assessed by sequencing of the amplicons that showed high nucleotide identities to Norovirus genogroup I/1, I/4, II/2, or II/4 clades, as well as to Astrovirus serotypes 1, 2, 4, or 8. The multiplex RT-PCR was also more sensitive than Astrovirus and Norovirus antigen enzyme immunoassays (IDEIA, Dako), as well as Astrovirus isolation in cell culture. This novel multiplex RT-PCR is an attractive technique for the rapid, specific, and cost-effective laboratory diagnosis of non-rotavirus acute gastroenteritis.

Comparison of two methods for the detection of hepatitis A virus in clam samples (Tapes spp.) by reverse transcription-nested PCR

The detection of hepatitis A virus in shellfish by reverse transcription-nested polymerase chain reaction (RT-nested PCR) is hampered mainly by low levels of virus contamination and PCR inhibitors in shellfish. In this study, we focused on getting a rapid and sensitive processing procedure for the detection of HAV by RT-nested PCR in clam samples (Tapes spp.). Two previously developed processing methods for virus concentration in shellfish have been improved upon and compared. The first method involves acid adsorption, elution, polyethylene glycol (PEG) precipitation, chloroform extraction and PEG precipitation. The second method is based on elution with a glycine buffer at pH 10, chloroform extraction and concentration by ultracentrifugation. Final clam concentrates were processed by RNA extraction or immunomagnetic capture of viruses (IMC) before the RT-nested PCR reaction. Both methods of sample processing combined with the RNA extraction from the concentrates were very efficient when they were assayed in seeded and naturally contaminated samples. The results show that the first method was more effective in removal inhibitors and the second was simpler and faster. The IMC of HAV from clam concentrates processed by method 1 was revealed to be a very effective method of simultaneously removing residual PCR inhibitors and of concentrating the virus.

Development and application of a capsid VP1 (region D) based reverse transcription PCR assay for genotyping of genogroup I and II noroviruses

Noroviruses (NoV), previously called "Norwalk-like viruses", have emerged as the single most important cause of acute gastroenteritis worldwide. Most diagnostic reverse transcription-polymerase chain reaction (RT-PCR) assays target the viral RNA-dependent RNA polymerase; however, the major capsid protein (VP1) is the reference genomic region for establishing genotypes. In this study, we analyzed complete NoV VP1 sequences (n=100) and determined a region (region D) that was most suitable to differentiate between genotypes. Within region D, we designed two genogroup specific, broadly reactive, degenerate primer sets (GI and GII). The region D primers were evaluated in a single-tube one-step RT-PCR assay using a panel of 81 (31 GI, 50 GII) NoV strains from both outbreaks and sporadic cases. In total, 95% of the samples tested positive using the new region D primer sets. Phylogenetic analysis of region D sequences (36 deduced amino acids for GI, 56 deduced amino acids for GII), revealed 19 clusters (7 within GI and 12 within GII) including three new genetically distinct clusters, two of which were unresolved using region A sequences. Phylogenetic analysis of the complete VP1 sequences revealed identical grouping of strains and confirmed the newly identified clusters using region D. In summary, we successfully developed and evaluated a broadly reactive RT-PCR assay for reliable genotyping of GI and GII noroviruses.

Norovirus capture with histo-blood group antigens reveals novel virus-ligand interactions

Noroviruses are genetically diverse, uncultivable, positive-sense RNA viruses and are the most common cause of epidemic acute gastroenteritis in humans in the United States. Recent studies of norovirus attachment in vitro by using recombinant virus-like particles (VLPs) suggest that various norovirus strains exhibit different patterns of attachment to ABH histo-blood group antigens, which are carbohydrate epitopes present in high concentrations on mucosal cell surfaces of the gut. However, attachment of live norovirus strains to histo-blood group antigens has not been investigated to date. Utilizing a newly designed magnetic bead-virus capture method, we characterized histo-blood group antigen attachment properties of various norovirus strains obtained from clinical stool specimens to compare the attachment properties of wild-type virus and VLPs and to further map norovirus attachment. Consistent with previous reports using VLPs, various strains of noroviruses exhibited different patterns of attachment to histo- blood group antigens. Norwalk virus bound specifically to H type 1, H type 3, and Le(b). Two genogroup II noroviruses, one representing the Toronto genotype and the other from a novel genotype, bound specifically to Le(b). A Desert Shield-like strain did not attach to H types 1, 2, or 3, H type 1 and 3 precursors, Le(a), or Le(b). Surprisingly, wild-type Snow Mountain virus (SMV) attached specifically to H type 3, which contradicted previous findings with SMV VLPs. On further investigation, we found that stool components promote this attachment, providing the first known observation that one or more components of human feces could promote and enhance norovirus attachment to histo-blood group antigens.

Simultaneous detection of enteric viruses by multiplex real-time RT-PCR

A multiplex real-time RT-PCR protocol for the simultaneous detection of noroviruses ("Norwalk-like viruses") of genogroups I and II, human astroviruses and enteroviruses is described. The protocol was developed and evaluated using the LightCycler and corresponding SYBR Green reagents. New primers were designed within conserved genome regions to optimize the detection range of virus subtypes of each genus. To enable the development of a multiplex PCR assay within one tube (capillary), similar mastermix- and cycling-conditions were respected for each individual primer system. Subsequent melting curve analysis allowed the determination of possible dual-contaminations of entero- and noro- or astroviruses by the formation of dual peaks. Special care was taken to minimize the loss of sensitivity, since the detection of small viral contaminations is a crucial parameter especially for food analysis. The multiplex assay was compared successfully to the single SYBR Green assay, and revealed to be at least 10 times more sensitive than the one obtained with an endpoint PCR thermocycler protocol published previously.

Laboratory efforts to cultivate noroviruses

Noroviruses (NoVs) are a leading cause of gastroenteritis worldwide and are recognized as the foremost cause of foodborne illness. Despite numerous efforts, routine cell cultures have failed to yield replicating NoV. This paper describes methods used to try to grow NoV in vitro in two laboratories. Cells (A549, AGS, Caco-2, CCD-18, CRFK, CR-PEC, Detroit 551, Detroit 562, FRhK-4, HCT-8, HeLa, HEC, HEp-2, Ht-29, HuTu-80, I-407, IEC-6, IEC-18, Kato-3, L20B, MA104, MDBK, MDCK, RD, TMK, Vero and 293) were cultured on solid or permeable surfaces. Differentiation was induced using cell culture supplements such as insulin, DMSO and butyric acid. In some cases, the cells and the NoV-containing stool samples were treated with bioactive digestive additives. Variables evaluated in cultivation experiments included the method of preparation of the virus inoculum, the genotype of the virus, conditions for maintenance of cell monolayers, additives in the maintenance medium and the method of inoculation of the cells. Serial blind passage studies were performed routinely. In addition to evaluation for CPE, evidence of virus replication was sought using immunofluorescent assays to detect newly produced viral capsid antigen and RT-PCR assays to detect the viral genome. Although some infected cultures remained NoV positive by RT-PCR for up to five passages and an occasional cell in a monolayer showed evidence of specific immunofluorescence, no reproducible NoV-induced CPE was observed and all RT-PCR results that were positive initially were negative following continued passaging. Thus, attempts to develop a method for the cultivation of NoV were unsuccessful.

Early identification of common-source foodborne virus outbreaks in Europe

The importance of foodborne viral infections is increasingly recognized. Food handlers can transmit infection during preparation or serving; fruit and vegetables may be contaminated by fecally contaminated water used for growing or washing. And modern practices of the food industry mean that a contaminated food item is not limited to national distribution. International outbreaks do occur, but little data are available about the incidence of such events and the food items associated with the highest risks. We developed a combined research and surveillance program for enteric viruses involving 12 laboratories in 9 European countries. This project aims to gain insight into the epidemiology of enteric viruses in Europe and the role of food in transmission by harmonizing (i.e., assessing the comparability of data through studies of molecular detection techniques) and enhancing epidemiologic surveillance. We describe the setup and preliminary results of our system, which uses a Web-accessible central database to track viruses and provides the foundation for an early warning system of foodborne and other common-source outbreaks.