Polymerase chain reaction detection of small round-structured viruses from two related hospital outbreaks of gastroenteritis using inosine-containing primers

Evaluation of the Impact of the Source (Patient Versus Staff) on Nosocomial Norovirus Outbreak Severity

Objective:

To study the dependence of infection risk and outbreak size on the type of index case (ie, patient or staff).

Methods:

Nosocomial outbreaks were reviewed and categorized into those started by patients and those started by staff. Infection risks and outbreak sizes were evaluated taking into account the index case category.

Results:

Of the 30 nosocomial outbreaks of norovirus with person-to-person transmission, 20 (67%) involved patients as the index cases. Patient-indexed outbreaks affected significantly more patients than did staff-indexed outbreaks (difference in means, 16.25; 95% confidence interval [CI95], 5.1 to 27.0). For the numbers of affected staff, no dependence on the index case category was detectable (difference in means, -1.05; CI95, -9.0 to 6.9). For patients exposed during patient-indexed outbreaks, the risk of acquiring a norovirus infection was approximately 4.8 times as high as the corresponding risk for patients exposed during staff-indexed outbreaks (odds ratio [OR], 4.79; CI95,1.82 to 8.28). The infection risk for exposed staff during patient-indexed outbreaks was approximately 1.5 times as high as the corresponding risk during staff-indexed outbreaks (OR, 1.51; CI95, 0.92 to 2.49).

Conclusions:

Patient-indexed norovirus outbreaks generally affect more patients than do staff-indexed outbreaks. Staff appear to be similarly affected by both outbreak index category groups. This study demonstrates the importance of obtaining complete outbreak data, including the index case classification as staff or patient, during norovirus outbreak investigations. Such information may be useful for further targeting prevention measures.

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.

Effective detection of human noroviruses in Hawaiian waters using enhanced RT-PCR methods

The current recreational water quality criteria using growth-based measurements of fecal indicator bacteria (FIB) concentration have their limitations for swimmer protection. To evaluate the possible use of enteric viruses as an improved indicator of human sewage contamination in recreational waters for enhanced health risk assessment, human norovirus (huNoV) was tested as a model in this study. To establish a highly sensitive protocol for effective huNoV detection in waters, 16 published and newly designed reverse transcription polymerase chain reaction (RT-PCR) primer pairs specific for huNoV genogroup I (GI) and genogroup II (GII) were comparatively evaluated side-by-side using single sources of huNoV RNA stock extracted from local clinical isolates. Under optimized conditions, these RT-PCR protocols shared a very different pattern of detection sensitivity for huNoV. The primer sets COG2F/COG2R and QNIF4/NV1LCR were determined to be the most sensitive ones for huNoV GII and GI, respectively, with up to 10(5)- and 10(6)-fold more sensitive as compared to other sets tested. These two sensitive protocols were validated by positive detection of huNoV in untreated and treated urban wastewater samples. In addition, these RT-PCR protocols enabled detection of the prevalence of huNoV in 5 (GI) and 10 (GII) of 16 recreational water samples collected around the island of O'ahu, which was confirmed by DNA sequencing and sequence analysis. Findings from this study support the possible use of enteric viral pathogens for environmental monitoring and argue the importance and essentiality for such monitoring activity to ensure a safe use of recreational waters.

Epidemiology and costs associated with norovirus outbreaks in NHS Lothian, Scotland 2007-2009

Healthcare-associated gastroenteritis outbreaks are becoming more common and are recognized challenges in hospital and community settings. In Edinburgh [NHS (National Health Service) Lothian], all the hospitals and the community were actively monitored for outbreaks of gastroenteritis from September 2007 to June 2009. In total, 1732 patients and 599 healthcare staff were affected in 192 unit outbreaks. In the acute sector, 1368 patients (0.99 cases/1000 inpatient bed-days) and 406 healthcare staff (0.29 cases/1000 inpatient bed-days) were affected in 155 unit outbreaks (0.23 unit outbreaks/day). Noroviruses were detected in 142 outbreaks (74%); 50 were not laboratory confirmed but were presumed to be noroviruses on epidemiological grounds. The closure of affected units to new admissions resulted in the loss of 3678 bed-days. By extrapolation, lost bed-days and staff absence due to gastroenteritis outbreaks cost NHS Lothian £1.2 million for the two norovirus seasons. Outbreaks in which the affected unit was closed within the first three days of recognizing the index case were contained in a mean of six days, and outbreaks in units that were closed later persisted for a mean of seven days; this difference was not statistically significant. Rapid implementation of control measures was effective in the control of outbreaks.

Genetic diversity of noroviruses and sapoviruses in children with acute sporadic gastroenteritis in New Delhi, India

BACKGROUND

Human caliciviruses (HuCVs) cause gastroenteritis throughout the world. Limited information is available on molecular epidemiology of caliciviruses from developing countries including India.

OBJECTIVES

Standardization and evaluation of a two-step multiplex RT-PCR assay for HuCVs and characterization of strains.

STUDY DESIGN

Two hundred and twenty-six stool samples were collected from children with acute gastroenteritis (AGE) over a one and half year to study the prevalence and diversity of HuCVs in children with AGE in New Delhi, India. A multiplex two-step RT-PCR using 3 sets of external and 4 sets of internal primers from the RdRp gene was standardized for detection of NoVs and SaVs. Molecular characterization of some HuCV strains was done by sequencing followed by phylogenetic analysis.

RESULTS

Fifty-nine HuCVs strains were detected in 54 (24%) of the samples; 5 samples had mixed infections. Of these 59 HuCVs, 36 (61%) were norovirus (34 were GGII; 2 were GGI) and 23 (39%) were sapovirus (22 were GGI; 1 was GGII). Phylogenetic analysis of partial RdRp gene of 12 HuCV strains identified three genotypes (GGI/4, GGII/3 and a newly identified GIIb/Hilversum cluster) in NoVs and one genotype (GGI/1) in SaVs.

CONCLUSION

This is one of the few reports from India on detection and characterization of HuCVs by multiplex RT-PCR assay. This assay can be a useful tool for epidemiological studies of HuCV infections.

Clinical characteristics of nosocomial norovirus outbreaks in Hong Kong

Norovirus outbreaks occur worldwide every year and have become more frequent over the last few years. There were extensive outbreaks in Hong Kong from May to July 2006 and our aim was to describe nosocomial outbreaks from 1 May 2006 to 31 July 2006 in this retrospective observational study. A total of 38 confirmed norovirus outbreaks involving 218 patients were identified. Most of these patients were elderly with a mean age of 74.5 years (range: 3 months to 97 years); 62% of them were either totally or partially dependent for help with daily activities, 83.9% had underlying chronic medical problems and 56% had limited mobility. In all, 97.2% of individuals presented with diarrhoea and only 46.3% of them had vomiting. The median duration for diarrhoea was 3 days and the longest 24 days. The median duration of vomiting was one day and the longest 15 days. Fever occurred in one-third of all cases. Reverse transcriptase-polymerase chain reaction was positive for norovirus in 72.6% cases. We conclude that nosocomial norovirus infection often involves frail elderly patients with limited mobility and that these patients may have more prolonged symptoms.

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.

Atypical norovirus epidemic in Hong Kong during summer of 2006 caused by a new genogroup II/4 variant

An atypically high level of norovirus activity was noticed in Hong Kong beginning in early May 2006. A study was carried out to investigate whether this was caused by a new norovirus variant. Epidemiological data including monthly positivity rates and the numbers of outbreaks per month from January to July 2006 were analyzed and compared to those from 2002 to 2005. In a comparison with the epidemiological data from 2001 to 2005, an atypical peak of norovirus-associated gastroenteritis outbreak was observed beginning in May 2006, concurring with a striking increase in norovirus activity. Most of the outbreaks (>60%) were located in homes for the elderly. Phylogenetic analysis for both RdRp and 5' capsid regions showed that this epidemic was caused by a new genogroup II/4 variant. This variant was genetically distinct from the predominant variants of 2002 and 2004 but was closely related to one of the 95/96-subset variants which caused an epidemic in Hong Kong in 2001, suggesting that the 95/96 subset may be starting to recirculate.

Rotavirus mortality confirmed by etiologic identification in Venezuelan children with diarrhea

BACKGROUND

Hospital-based studies to determine the etiology of deaths from diarrhea are scarce. In this study, we specifically analyzed deaths due to rotavirus to assess the rotavirus impact on diarrhea mortality.

METHODS

To determine the rotavirus proportion contributing to mortality due to diarrhea, we analyzed data obtained from a hospital-based mortality surveillance, conducted over 7 years, in the Ciudad Hospitalaria Dr. Enrique Tejera, Valencia, Venezuela. Rotavirus was identified in stool samples collected from children who died of diarrhea, by a confirmatory ELISA and/or reverse transcription polymerase chain reaction.

RESULTS

Our results show that rotavirus (21%; 21/100) is the leading cause of death due to diarrhea among children <5 years of age; rotavirus also has an important impact (2%; 21/1336) on deaths from all causes in this age group. Shigella spp. (19%; 13/69) was the second most important cause of death, followed by calicivirus (6%; 3/53). Furthermore, this study documents a seasonal pattern in the deaths due to rotavirus (odds ratio 3.28; 95% confidence interval 1.13-9.76).

CONCLUSIONS

For Venezuela, it is estimated that approximately 300 children <5 years of age die of rotavirus each year, which means that 1 in 1800 children die by the age of 5. Rotavirus was found to be the main cause of death due to diarrhea, which supports previous estimations. This is the first study to present data of cause-specific mortality due to diarrhea based on hospital surveillance of diarrhea etiologies.

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.

Correlation of norovirus variants with epidemics of acute viral gastroenteritis in Hong Kong

Norovirus (NV) (formerly called Norwalk-like virus) is the most common etiological agent of acute viral gastroenteritis outbreaks worldwide. Recent reports have shown that two new GII.4 variants caused epidemics in Europe. To investigate if it is also the case in Hong Kong, a molecular epidemiological study was undertaken between January 2002 and June 2005. During this period, there was a substantial increase in acute cases of gastroenteritis caused by NV. Phylogenetic analysis showed that GII.2 and GII.4 are the major circulating genotypes. Two new GII.4 variants (variants C and D) were identified in 2002 and 2004, which quickly became the predominant strains. They were almost identical to the variants causing epidemics in Europe recently. Since geographically distinct areas were involved within a short period of time, it is possible that GII.4 has a particular propensity for causing pandemics.

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.

Molecular detection of porcine enteric caliciviruses in Venezuelan farms

Caliciviruses are a well-established cause of respiratory, vesicular and hemorrhagic diseases in animals. In addition, these viruses are an important cause of enteric diseases in humans. Recently, molecular analysis of several porcine enteric caliciviruses indicated that they are closely related to human enteric caliciviruses. The objective of this work was to determine the frequency, age distribution, and association with diarrhea of enteric calicivirus infections in piglets and to partially characterize the detected isolates. A total of 203 stool samples from animals 0 to 9 weeks of age, collected between 1993 and 2003 in seven porcine farms located in the central region of Venezuela were tested for enteric caliciviruses by reverse transcription-polymerase chain reaction (RT-PCR) amplification using primers designed to detect both norovirus and sapovirus. Selected amplicons were sequenced to establish phylogenetic relationships with reference strains. Calicivirus were detected in 18% (36/204) of the samples. Viruses were detected more frequently in animals between 3 and 4 weeks of age, and were detected in samples from animals with diarrhea and without diarrhea with equal frequencies (14 versus 19%, p>0.5). Phylogenetic studies based on partial RNA polymerase gene sequences indicated that the Venezuelan isolates were most closely related (75-95% identity) to the sapovirus Cowden reference strain. These results provide evidence that caliciviruses of the genus sapovirus circulate frequently in piglets but further studies are needed to clarify their importance as cause of diarrhea.

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.

Rapid control of norovirus gastroenteritis outbreak in an acute paediatric ward

AIM

To provide a practical action plan for effective infection control of norovirus outbreak in acute paediatric wards.

METHODS

We report the infection control measures that were implemented to terminate and to prevent nosocomial spread of norovirus gastroenteritis in an open-designed paediatric ward.

RESULTS

Nine children, one visitor, and one medical student were affected in a norovirus gastroenteritis outbreak in an acute paediatric ward. Vomiting was the main presenting symptom. The outbreak was rapidly terminated three days after implementation of stringent infection control measures and there was no second wave of attack. These measures included strict contact precautions, prompt isolation and cohorting of symptomatic patients, vigorous environmental cleansing with concentrated disinfectant (hypochlorite solution 1000 ppm), meticulous handling of waste products, and efficient contact tracing of exposed patients, family members, and medical students.

CONCLUSION

Prompt implementation of stringent infection control measures and contact tracing can rapidly terminate the norovirus outbreak and prevent a second wave of infection. Children with unexplained vomiting and those with contact history of gastroenteritis should be properly triaged, isolated, and investigated for possible infective causes, including norovirus-induced gastroenteritis.

Genomic characterization of the unclassified bovine enteric virus Newbury agent-1 (Newbury1) endorses a new genus in the family Caliciviridae

The pathogenic bovine enteric virus, Newbury agent-1 (Bo//Newbury1/1976/UK), first identified in 1976, was characterized as a possible calicivirus by morphology, buoyant density in CsCl and the presence of a single capsid protein but genomic sequence could not be obtained. In the present study, the complete genome sequence of Newbury1 was determined and classified Newbury1 in a new genus of the Caliciviridae. The Newbury1 genome, of 7454 nucleotides, had two predicted open reading frames (ORFs). ORF1 encoded the non-structural and contiguous capsid proteins. ORF2 encoded a basic protein characteristic of the family Caliciviridae. Compared to the 4 recognized Caliciviridae genera, Norovirus, Sapovirus, Lagovirus and Vesivirus, Newbury1 had less than 39% amino acid (47% nucleotide) identity in the complete 2C-helicase, 3C-protease, 3D-polymerase and capsid regions but had 89% to 98% amino acid (78% to 92% nucleotide) identity to the recently characterized NB virus in these regions. By phylogenetic analyses, Newbury1 and NB viruses formed a distinct clade independent of the 4 recognized genera. However, amino acid identities showed that Newbury1 and the NB virus were distinct polymerase types (90% amino acid identity), but their complete capsid proteins were almost identical (98% amino acid identity). Analyses of contemporary viruses showed that the two polymerase genotypes, Newbury1 and NB, were circulating in UK cattle and antibody to Newbury1-like viruses was common in cattle sera. The present study defined the existence of a new genus in the Caliciviridae that we propose be named Becovirus or Nabovirus to distinguish the new clade from bovine noroviruses.

Calicivirus infection in human immunodeficiency virus seropositive children and adults

BACKGROUND

The importance of enteric viral infections in HIV-related diarrhea is uncertain. Human caliciviruses have emerged as a leading cause of acute diarrhea worldwide.

OBJECTIVES

To evaluate the importance of calicivirus infections in HIV-related diarrhea. Study design 151 fecal samples collected from children and adults infected with HIV, with and without diarrhea, were examined. In addition, 89 fecal samples from non HIV-infected children and adults were also tested. Samples were analyzed by RT-PCR using primer sets specific to Norovirus genogroup I or genogroup II as well as primers designed to react with both Noroviruses and Sapovirus genus.

RESULTS

Viruses were detected with equal frequencies in stools from HIV infected and non-infected adults (12%). However, specimens from HIV infected children were more likely than those of HIV-negative children to have caliciviruses (51% versus 24%, P<0.05). Viral infections were not significantly associated with diarrhea neither in children nor in adults, regardless of HIV status. Viruses genetically related to the common Lordsdale virus (Norovirus genogroup II) and London/92 virus (Sapovirus) clusters were detected circulating among children.

CONCLUSIONS

These results suggest that caliciviruses may be an important opportunistic pathogen in children infected with HIV.

Detection of Viral, Bacterial, and Parasitological RNA or DNA of Nine Intestinal Pathogens in Fecal Samples Archived as Part of the English Infectious Intestinal Disease Study

Fecal samples were collected from cases and controls as part of the Infectious Intestinal Disease (IID) study in England and were stored as frozen suspensions for 8 to 12 years. The purpose of this study was to apply PCR-based procedures to assess the stability of pathogen-specific nucleic acid sequences present in this archive. Samples from which Cryptosporidium, Giardia, Salmonella, Campylobacter, enteroaggregative Escherichia coli (EAggEC), enterotoxigenic Clostridium perfringens, rotaviruses, noroviruses, or sapoviruses had been previously detected during the IID study using conventional methods were selected from the archive. A generic nucleic acid extraction method to recover RNA or DNA was used. Complementary DNA was generated from RNA by reverse transcription with random priming. Block-based and real-time PCR assays were used to amplify and detect gene fragments from each of these pathogens. The percentage reconfirmation of target was as follows: Giardia duodenalis 68%, Cryptosporidium 96%, Campylobacter 98%, Salmonella 98%, enterotoxigenic C perfringens 34%, EAggEC 93.3%, rotavirus 95%, norovirus 73%, and sapovirus 85%. This study has shown that nucleic acid can be extracted and specific sequences amplified and detected from archived fecal samples. The IID archive therefore represents a valuable resource for further studies, especially the investigation of the samples from which no pathogens had previously been detected.

Diversity of enteric viruses detected in patients with gastroenteritis in a tertiary referral paediatric hospital

The genetic diversity of enteric viruses co-circulating in a cohort of patients with viral gastroenteritis in a large tertiary paediatric hospital in London, UK, was determined. Multiple strains of noroviruses (NV), sapoviruses (SV) and astroviruses (HAsV) were detected in these patients, indicating the likelihood of multiple introductions from different sources, possible sub-clinical infections and simultaneous infection with different viruses in immunocompromised and other patients. Routine screening of immunocompromised patients and infection control procedures are important to prevent nosocomial infection.

Epidemiology and cost of nosocomial gastroenteritis, Avon, England, 2002-2003

Implementing control measures rapidly may be effective in controlling gastroenteritis outbreaks.

Healthcare-associated outbreaks of gastroenteritis are an increasingly recognized problem, but detailed knowledge of the epidemiology of these events is lacking. We actively monitored three hospital systems in England for outbreaks of gastroenteritis in 2002 to 2003. A total of 2,154 patients (2.21 cases/1,000-hospital-days) and 1,360 healthcare staff (0.47 cases/1,000-hospital-days) were affected in 227 unit outbreaks (1.33 outbreaks/unit-year). Norovirus, detected in 63% of outbreaks, was the predominant etiologic agent. Restricting new admissions to affected units resulted in 5,443 lost bed-days. The cost of bed-days lost plus staff absence was calculated to be £635,000 (U.S.$ 1.01 million) per 1,000 beds. By our extrapolation, gastroenteritis outbreaks likely cost the English National Health Service £115 million (U.S.$ 184 million) in 2002 to 2003. Outbreaks were contained faster (7.9 vs. 15.4 days, p = 0.0023) when units were rapidly closed to new admissions (<4 days). Implementing control measures rapidly may be effective in controlling outbreaks.

Asymptomatic and symptomatic excretion of noroviruses during a hospital outbreak of gastroenteritis

During an investigation of a hospital outbreak of norovirus gastroenteritis identified as being caused by a recombinant genogroup II (rGII-3a) strain, fecal specimens collected from asymptomatic staff and patients were tested by nested PCR. A GII-4 norovirus strain, the predominant strain associated with outbreaks in hospitals over the last few years, was detected in 26 and 33% of asymptomatic staff and patients, respectively. No rGII-3a (Harrow/Mexico) norovirus strains were detected in the samples of asymptomatic staff or patients.

A chimeric bovine enteric calicivirus: evidence for genomic recombination in genogroup III of the Norovirus genus of the Caliciviridae

The Norovirus genus of the Caliciviridae encompasses viruses that cause outbreaks of gastroenteritis in human and viruses that have been associated with diarrhea in cattle. The two bovine noroviruses, Bo/Newbury2/76/UK and Bo/Jena/80/DE, represent two distinct genetic clusters in the newly described genogroup III. In the present study, Jena-like polymerase sequences were identified for the first time in the UK, but one of these, Bo/Thirsk10/00/UK, was a chimeric virus. Bo/Thirsk10/00/UK had a Jena-like polymerase gene but Newbury2-like capsid and ORF3 genes by comparison of their genome organization, nucleotide, and amino acid identities and phylogenetic analyses. The present study is one of few studies to clearly demonstrate the existence of chimeric genomes in the Norovirus genus and the first, to our knowledge, to identify a chimeric genome in genogroup III. It provides additional support that genomic recombination is part of the natural evolution of noroviruses and is relevant to the diagnosis and immunological control of norovirus diarrhea outbreaks.

Coexistence of multiple genotypes, including newly identified genotypes, in outbreaks of gastroenteritis due to Norovirus in Japan

Norovirus (NV) (formerly called Norwalk-like virus) is the most common cause of acute nonbacterial gastroenteritis in humans. Recently, we reported an NV genotyping scheme based on variability in the capsid N-terminal/shell (N/S) domain gene (Katayama et al., Virology 299:225-239, 2002). We found 19 genotypes, including nine of genogroup I and 10 of genogroup II. In the present study, we investigated the molecular epidemiology of NV from 66 outbreaks that occurred in Saitama Prefecture, Japan, from 1997 to 2002. We screened 416 stool specimens by a real-time reverse transcription (RT)-PCR method (Kageyama et al., J. Clin. Microbiol. 41:1548-1557, 2003) and detected 156 NV-positive specimens, from which we amplified the capsid N/S domain gene by RT-PCR and then cloned the PCR products. After sequencing these clones, we obtained 368 sequence variants (strains). By applying our classification scheme to the strains from Saitama and other published strains, we identified a total of 31 genotypes, including an additional five genotypes for genogroup I and seven for genogroup II. Of the 31 genotypes, 26 were present in the Saitama area during that time period. These results provide additional evidence for the great diversity of human NV genotypes. Specimens from all shellfish-related infections contained multiple genotypes, including several new genotypes. On the other hand, single genotypes were observed mostly in outbreaks that originated in semiclosed communities. Thus, the number of NV genotypes in each outbreak depended on the route of transmission.

Diversity of noroviruses cocirculating in the north of England from 1998 to 2001

A study was undertaken to investigate the diversity of noroviruses (NVs) in fecal samples from patients from 529 outbreaks and 141 sporadic cases of gastroenteritis in the North of England from September 1998 to August 2001. NV strains were detected by electron microscopy and characterized by a combination of the Grimsby virus antigen enzyme-linked immunosorbent assay, reverse transcriptase PCR, the heteroduplex mobility assay, and DNA sequencing. Twenty-one distinct NV strains, including several novel or variant strains not seen previously, were found circulating in the population studied. Genogroup II NVs were responsible for 83% of the outbreaks. Several strains cocirculated at any one time. The Bristol (Grimsby/Lordsdale) and Hawaii (Girlington) genotypes were the most prevalent among the NVs identified, detected in 49 and 20% of the outbreaks, respectively. A limited number of other genogroup II and I strains were cocirculating. The virus populations detected in hospitals and nursing homes were distinct from those found in community-based outbreaks. Outbreaks in hospitals and nursing homes were more likely to be caused by genogroup II strain Grimsby or Girlington (P < 0.0001) than by other genogroup II or I strains.

Clinical manifestation of norovirus gastroenteritis in health care settings

Noroviruses are generally believed to cause relatively mild gastroenteritis of short duration in otherwise healthy adults. However, outbreaks in health care settings are common and affect vulnerable populations. During 2002-2003, a total of 4 major hospitals, 11 community hospitals, and 135 nursing homes in the county of Avon, England, were prospectively monitored for outbreaks of gastroenteritis. For 482 hospital staff, 166 nursing home staff, and 266 nursing home residents, the median duration of norovirus gastroenteritis was 2 days, with 75% achieving complete recovery within 3 days. The median duration of norovirus gastroenteritis for 730 hospital patients was 3 days (75% of the patients achieved complete recovery within 5 days), which was significantly longer than that for all other groups (P<.001). Therefore, infection in hospitalized persons may be more severe than that in other groups in the community at large. This increased duration of acute illness should be considered when implementing measures to prevent transmission in hospital settings.

National epidemic of Lordsdale Norovirus in the UK

BACKGROUND

In early 2002 reports of outbreaks of gastroenteritis reached unprecedented levels in the UK. Forty five Norovirus outbreaks were reported in January 2002.

OBJECTIVES

The objective of the study was to determine whether the outbreaks were Noroviral in origin and if so whether they represented a homogeneous or heterogeneous collection of Noroviruses by applying EIA and sequence analysis to representative faecal samples.

STUDY DESIGN

Faecal specimens were collected during the week of highest incidence from 21 outbreaks in a variety of health care settings including hospitals and nursing homes. The outbreaks occurred in geographically distinct regions of the UK and samples were collected by reference laboratories in Glasgow, Manchester, Bristol and Southampton.

RESULTS

The samples were all positive for Noroviruses by negative stain electron microscopy (EM) and Lordsdale virus (LV) EIA, therefore reverse transcriptase polymerase chain reaction (RT-PCR) amplification and nucleotide sequencing of the Norovirus RNA polymerase gene was performed on amplicons from samples of each of the 21 outbreaks to investigate the nature and extent of diversity. All samples were very closely related to the reference Lordsdale virus genome sequence. LV was first discovered during an hospital outbreak of gastroenteritis in Southampton General Hospital in March 1993.

CONCLUSIONS

Noroviruses are a major cause of outbreaks of gastroenteritis in health care settings. LV is the predominant Norovirus in the UK and was detected in outbreaks that occurred during the national peak of gastroenteritis reports in January 2002.

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.

Primer pair p289-p290, designed to detect both noroviruses and sapoviruses by reverse transcription-PCR, also detects rotaviruses by cross-reactivity

A primer pair (p289-p290) designed to detect both noroviruses and sapoviruses by reverse transcription-PCR (Jiang et al., J. Virol. Methods 83:145, 1999) cross-reacts with rotaviruses. The rotavirus amplicon corresponds to genome segment 1. Furthermore, primer pair p289-p290 detected rotaviruses as efficiently as rotavirus-specific primers directed to rotavirus gene 4.

Methods for the detection and characterisation of noroviruses associated with outbreaks of gastroenteritis: Outbreaks occurring in the north-west of England during two norovirus seasons

This article describes the methods used to investigate 407 outbreaks of acute non-bacterial gastroenteritis occurring in the North-West of England between January 2000 and July 2001 and suspected to be caused by noroviruses (NV) [Mayo (2002) Arch Virol 147:1655-1663]. These included 319 outbreaks in hospitals and nursing homes and 88 other settings. Eight hundred and seventy-one faecal samples from 407 outbreaks were tested using electron microscopy (EM), an enzyme-linked immunosorbent assay (ELISA) specific for Grimsby virus (GRV) capsid antigen and/or by reverse transcriptase-polymerase chain reaction (RT-PCR) for NV, allowing the utility of each assay for routine diagnosis to be assessed. Preliminary genomic characterisation of detected strains was performed using the heteroduplex mobility assay (HMA) and DNA sequencing. The results demonstrate the continuing predominance of GII-4 GRV strain of NV as a cause of outbreaks, particularly in hospital and nursing home settings. Overall, NV were detected in 223/407 (55%) of outbreaks tested. However, a wide range of apparently diverse strains was identified, including several not previously reported. Genomic characterisation revealed clusters of linked outbreaks not recognised previously.

High rate and changing molecular epidemiology pattern of norovirus infections in sporadic cases and outbreaks of gastroenteritis in Hong Kong

Noroviruses (Norwalk-like viruses (NLV)) are recognised as major causes of acute gastroenteritis worldwide. Numerous studies had been carried out on the molecular epidemiology of norovirus in outbreaks but relatively few on sporadic cases. In this study, the molecular epidemiology of noroviruses in sporadic and outbreak cases of acute gastroenteritis in Hong Kong was examined over a 12-month period from July 2001 to June 2002. Specimens from three groups of patients were used in this study. Nine hundred ninety-five specimens from patients enrolled in the Acute Diarrhoeal Diseases Surveillance Programme of the Department of Health, Hong Kong Government; 735 clinical specimens from hospital patients with acute gastroenteritis, and 122 specimens from 44 norovirus outbreaks. Ninety-two (9.2%) surveillance specimens were positive for norovirus RNA by reverse transcription-polymerase chain reaction (RT-PCR), compared to 123 (16.7%) clinical and 101 (82.8%) outbreak specimens. For the first 6 months of the study period, the predominant strain was the Bristol strain that belongs to genogroup II (GII). In the latter 6 months of the study, genogroup I (GI) and strains belonging to other clusters of GII were seen more commonly. The vast majority of strains belonging to the Bristol virus cluster were closely related to the 95/96-US subset that was associated with pandemic infection from 1995 onwards. This study clearly establishes the importance of norovirus as a cause of sporadic cases of acute gastroenteritis in all age groups in Hong Kong.

Precise characterization of norovirus (Norwalk-like virus)-specific monoclonal antibodies with broad reactivity

We have been characterizing monoclonal antibodies against Norovirus (Norwalk-like virus). In the course of our study, two monoclonal antibodies generated against Norovirus genogroup II capsid protein were found to react not only to genogroup II but also to genogroup I recombinant capsid proteins. In addition, we showed that these two monoclonal antibodies reacted to a 40-amino-acid-fragment located close to the N-terminal region of genogroup II Norovirus. Similar reactivity was observed with the equivalent region of genogroup I Norovirus. In this study, we confirmed that the epitopes of the two monoclonal antibodies existed within an 11-amino-acid peptide. To obtain an idea of the reactive ranges of the two monoclonal antibodies toward different strains of Norovirus, their reactivities were investigated using 16 types of peptide constructed according to the data in GenBank and 8 recombinant capsid proteins (7 whole capsid proteins and 1 short [80-amino-acid] protein fragment). A characteristic broad reactivity of the two monoclonal antibodies is clearly shown by the results of this study. Thus, these monoclonal antibodies could be useful tools for detecting a broad range of Norovirus strains.

Molecular characterization of bovine enteric caliciviruses: a distinct third genogroup of noroviruses (Norwalk-like viruses) unlikely to be of risk to humans

Bovine enteric caliciviruses (BoCVs) have been classified in the Norovirus (Norwalk-like virus) genus of the Caliciviridae, raising questions about zoonotic transmission and an animal reservoir for the human Norwalk-like viruses (NLVs), an important cause of nonbacterial gastroenteritis in humans. We examined the genetic relationship of human NLVs to BoCVs that were identified by using reverse transcription-PCR with primer pairs originally designed to detect human NLVs. Polymerase, capsid, and open reading frame 3 (ORF3) gene sequence analyses of BoCVs that were identified from 1976 to 2000 from throughout the United Kingdom showed that BoCVs formed a distinct third genogroup of closely related viruses distinct from the human genogroup I and II NLVs. Evidence was not obtained to support the concept that BoCVs are circulating in humans and pose a threat to human health.

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

A commercially available enzyme immunoassay, the IDEIA Norwalk-like virus (NLV) enzyme linked immunosorbent assay (ELISA; Dako Cytomation, Ely, UK) for detecting NLV antigen in faecal samples and determining the NLV genogroup was evaluated. The performance of the ELISA was compared with that of electron microscopy and the reverse transcription polymerase chain reaction by testing a panel of faecal samples collected from patients involved in outbreaks of gastroenteritis. When compared with reverse transcription-polymerase chain reaction (RT-PCR), the ELISA had a sensitivity and specificity of 55.5 and 98.3%, respectively. This compares with a sensitivity and specificity for EM of 23.9 and 99.2%, respectively. The sensitivity and specificity of the ELISA for determining the aetiology of a Norwalk virus-like outbreak, based on two or more positive samples within an outbreak, were 52.2 and 100% when two samples were collected from an outbreak and 71.4 and 100% when six or more samples were collected. The ELISA correctly identified the NLV genogroups of viruses previously characterised by partial DNA sequencing. The ELISA is a suitable alternative to the preliminary screening by EM for investigating outbreaks of gastroenteritis. Outbreaks, negative by ELISA should be examined by RT-PCR in order to detect strains non-reactive in the assay and virus strains from representative ELISA positive outbreaks should be characterised fully to allow the genetic diversity of NLVs co-circulating in the population to be described.

Surveillance of norovirus infection in a study of sporadic childhood gastroenteritis in South West England and South Wales, during one winter season (1999-2000)

Reverse transcriptase polymerase chain reaction (RT-PCR), electron microscopy (EM) and a genotype II specific antigen capture enzyme immunoassay (EIA), (Lordsdale strain) were used to establish the prevalence of Norwalk-like viruses (NLV) among sporadic cases of childhood gastroenteritis in South West England over a winter season. Samples of 3,172 stools from cases of gastroenteritis in children aged under 7 years sent to the Bristol Public Health Laboratory over the 1999/2000 winter 'season' were tested prospectively by EM, EIA and RT-PCR. The results from sporadic cases were compared with 1,360 samples from 285 outbreaks of gastroenteritis which were sent to the laboratory over the same period. In total NLV was established as the causal agent in 326 cases (10.3%) of sporadic gastroenteritis by one or more of the tests (EM 30 (0.9%), EIA 132 (4.2%) and RT-PCR 276 (8.7%)). The presence of other enteric viruses was established using EM and rotavirus EIA. Rotaviruses were the most common cause of viral gastroenteritis with 684 cases (21.6%). Other viruses detected included, adenovirus 124 cases (3.9%), astrovirus 97 cases (3.1%) and calicivirus in 7 cases (0.2%). NLV was the second most common viral agent indicating a significant role in cases of sporadic childhood gastroenteritis.

Characterization of an enteropathogenic bovine calicivirus representing a potentially new calicivirus genus

Bovine enteric caliciviruses (BEC) are associated with diarrhea in young calves. The BEC strains detected in Europe form a third genogroup within the genus "Norwalk-like viruses" (NLV) of the family Caliciviridae. In this report, we present sequence, clinical, and histological data characterizing a novel enteropathogenic BEC strain, NB, detected in fecal specimens from calves in the United States. The complete RNA genome of the NB virus is 7,453 bases long and is organized into two open reading frames (ORFs). ORF-1 is 2,210 amino acids long and encodes a large nonstructural polyprotein contiguous with the major capsid protein (VP1), similar to the lagoviruses and "Sapporo-like viruses" (SLV). The conserved calicivirus motifs were identified in the nonstructural proteins. ORF-2 is located at the 3' end of the genome and encodes a small basic protein (VP2) of 225 amino acids. The 5' and 3' untranslated regions are 74 and 67 bases long, respectively. Among caliciviruses, NB virus shows amino acid identities of 14.1 to 22.6% over the entire ORF-1 nonstructural-protein sequence with NLV, SLV, vesivirus, and lagovirus strains, while the overall sequence identity of the complete NB VP-1 with other caliciviruses is low, varying between 14.6 and 26.7%. Phylogenetic analysis of the complete VP1 protein, including strains from all four calicivirus genera, showed the closest grouping of NB virus to be with viruses in the genus Lagovirus, which cause liver infections and systemic hemorrhage in rabbits. In gnotobiotic calves, however, NB virus elicited only diarrhea and intestinal lesions that were most severe in the upper small intestine (duodenum and jejunum), similar to the NLV BEC strains. The tissues of major organs, including the lung, liver, kidney, and spleen, had no visible microscopic lesions.

Detection and differentiation of Norwalk virus by reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay

We have developed a reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay (RT-PCR-ELISA), using genetic cluster-specific probes in a microtiter plate format, for the detection and differentiation of Norwalk virus (NV) in stool samples. The specificity of the RT-PCR-ELISA was confirmed by testing 76 stool specimens and 15 tissue culture fluids derived from growths of unrelated viruses. The sensitivity of the RT-PCR-ELISA was compared with conventional PCR and Southern hybridization by testing the four cDNA clones derived from the RNA-dependent RNA polymerase region of the NV68 (NV/GI) virus and viruses in the NV/GII/P1B, the NV/GII/P2A, and the NV/GII/P2B cluster. This assay was as sensitive as the conventional RT-PCR with Southern hybridization regardless of primer pairs and probes used in the experiments. However, the actual sensitivity of this method was higher when clinical stool samples were examined because this assay examines all the samples irrespective of the RT-PCR results. The RT-PCR-ELISA format is simple, time saving, and suitable for testing many samples. It should be reliable for large-scale epidemiological studies of NV.

Epidemiology of acute viral gastroenteritis in children hospitalized in Rouen, France

This study assessed the epidemiologic characteristics of acute viral gastroenteritis in hospitalized children. A stool sample obtained from each child was analyzed for the presence of astrovirus, calicivirus, rotavirus, adenovirus, enterovirus, and digestive bacteria. Of the 438 stool samples obtained, 138 tested positive for > or =1 pathogen during the winters of 1997-1998 and 1998-1999 (P<.001). Virologic tests revealed rotavirus in 17.3% of samples, calicivirus in 7.3%, astrovirus in 6.8%, adenovirus in 0.7%, and > or =1 virus in 5.4%. Median age was higher for patients with rotavirus gastroenteritis than it was for those with astrovirus or calicivirus gastroenteritis (P=.014). Mean duration of hospitalization was statistically significantly lower for children with rotavirus gastroenteritis (P=.022), despite the more-frequent dehydration observed among children with rotavirus versus those with astrovirus or calicivirus gastroenteritis (P=.007). In contrast, enteral rehydration was more rapidly achieved in patients with gastroenteritis due to rotavirus.

Evaluation of nine sets of PCR primers in the RNA dependent RNA polymerase region for detection and differentiation of members of the family Caliciviridae, Norwalk virus and Sapporo virus

Norwalk virus and Sapporo virus were approved as type species of the genus "Norwalk-like viruses" and the genus "Sapporo-like viruses," respectively, in the family Caliciviridae. A total of 116 stool specimens containing Norwalk virus (NV) or Sapporo virus (SV) were tested by RT-PCR and Southern hybridization to evaluate nine sets of PCR primers and seven internal oligonucleotide probes in the RNA dependent RNA polymerase region of NV and SV for detection and differentiation of viruses in the NV and SV. Fifty-five stool samples were collected from 11 outbreaks of NV and/or SV gastroenteritis in an infant home, where residents were infants under 2 years of age, in Sapporo, Japan. Sixty specimens were obtained in Sapporo from sporadic cases in children, mainly under 6 years of age, of acute gastroenteritis due to small round structured viruses detected by EM. There is no single primer pair to detect all NV and SV, and at least three primer pairs, G1 set, G2 set and Sapp35/Sapp36, are required to detect viruses in the NV and SV clades. Many NV and SV strains were successfully classified into one of the NV/genogroup I, NV/genogroup II and SV by single-round RT-PCR and Southern hybridization. The new detection method for SV reported in this study combined with those for NV previously reported may elucidate the importance of Norwalk virus and Sapporo virus as a cause of viral gastroenteritis in all age groups in the world.

Diagnosis of noncultivatable gastroenteritis viruses, the human caliciviruses

Gastroenteritis is one of the most common illnesses of humans, and many different viruses have been causally associated with this disease. Of those enteric viruses that have been established as etiologic agents of gastroenteritis, only the human caliciviruses cannot be cultivated in vitro. The cloning of Norwalk virus and subsequently of other human caliciviruses has led to the development of several new diagnostic assays. Antigen detection enzyme immunoassays (EIAs) using polyclonal hyperimmune animal sera and antibody detection EIAs using recombinant virus-like particles have supplanted the use of human-derived reagents, but the use of these assays has been restricted to research laboratories. Reverse transcription-PCR assays for the detection of human caliciviruses are more widely available, and these assays have been used to identify virus in clinical specimens as well as in food, water, and other environmental samples. The application of these newer assays has significantly increased the recognition of the importance of human caliciviruses as causes of sporadic and outbreak-associated gastroenteritis.

Detection of sporadic cases of Norwalk-like virus (NLV) and astrovirus infection in a single Irish hospital from 1996 to 1998

BACKGROUND

'Norwalk-like viruses' (NLV) and astroviruses are recognised as the most important etiologic agents of viral gastroenteritis, excluding rotaviruses. However, neither of these two groups of viruses is routinely screened for in Irish hospital laboratories.

OBJECTIVE

The objective of this study was to examine faeces collected from patients with non-bacterial, non-rotaviral gastroenteritis and examine if NLVs and astroviruses could be identified as the causative agents of the illness.

STUDY DESIGN

Faecal specimens were collected from a single Irish hospital from February 1996 to June 1998. Three hundred and sixty samples were tested for the presence of NLVs using newly designed inosine-containing degenerate primers. Two hundred and three faecal specimens from paediatric patients were screened for the presence of astroviruses.

RESULTS

the results of the screening study were that 29 (8%) specimens were found to be positive for NLV by reverse transcription polymerase chain reaction (RT-PCR) and 15 (7%) specimens from paediatric patients were found to be positive for astroviruses. Genotyping of the NLV-positive samples determined that four of the isolates were from genotype I (G1) and 25 were G2. The G2 positive specimens were further subtyped by oligonucleotide probing and the majority (n = 21) were found to be subtype P2-B, with four isolates being typed as P2-A. No P1-B isolates were found.

CONCLUSIONS

This is the first report of detection of sporadic cases of NLV and astrovirus in Ireland. The results obtained highlight the need for continued surveillance of these viruses and the development of rapid detection systems for use in clinical laboratories.

Viruses and bivalve shellfish

The epidemiological data clearly demonstrates that filter feeding bivalve shellfish can, and do, act as efficient vehicles for the transmission of enteric viruses transmitted by the faecal-oral route. This identified hazard has been documented as a cause for concern by various international agencies and has a long history. Disease outbreaks can occur on an epidemic scale as graphically illustrated by an outbreak of Hepatitis A in Shanghai, China in 1988 involving about 300,000 cases. Improvement of harvesting area water quality offers the most sustainable route to improvement in the virological quality of bivalve shellfish sold live. However there is growing awareness, and concern, that current regulatory standards based on faecal coliform monitoring do not fully protect the shellfish consumer from viral infection. New viral test methods based on PCR, and the development of alternative more reliable faecal pollution indicators, offer new approaches for the further development of public health controls. However, further work is required to build a scientific consensus and to understand the implications of their introduction into legislation.

The heteroduplex mobility assay (HMA) as a pre-sequencing screen for Norwalk-like viruses

Molecular epidemiological studies of Norwalk-like viruses (NLVs), previously known as small round structured viruses (SRSVs), are dependant currently on DNA sequencing of PCR amplicons, which is expensive and time consuming. The Heteroduplex Mobility assay (HMA) was evaluated as a method for identification of PCR amplicons from the commonly circulating NLV strains without DNA sequencing. The procedure was developed for use with two reference strains, a Mexico virus-like strain (MXV-like; Hu¿NLV¿RBH¿1993¿UK) and the Grimsby virus strain (Hu¿NLV¿Gimsby¿1995¿UK), and was optimised with regards to the annealing and electrophoresis conditions and the electrophoresis gel matrix. Using the optimised conditions, amplicons of less than 90% sequence identity formed visible heteroduplexes, allowing the strains to be placed into three categories; Mexico-like, Grimsby-like and non-Mexico virus/non-Grimsby virus strains. Outbreak strains 'genotyped' previously by DNA sequencing as Mexico virus or Grimsby virus were identified correctly by the heteroduplex mobility assay. The procedure was applied prospectively to strains from 130 outbreaks occurring in the UK between 1997 and 1998. Heteroduplex mobility assay was successful on 120 (92%) strains of which 68 (57%) were GRV-like strains, three (2.5%) were Mexico virus-like strains and 49 (41%) were categorised as non- Mexico/non-Grimsby virus strains. Amplicons from 50 of the 120 strains were sequenced and there was perfect correlation between the heteroduplex mobility assay categorisation and phylogenetic analysis. HMA offers a rapid, robust and far cheaper alternative to sequencing for the identification of prevalent Norwalk-like virus genotypes for molecular epidemiological studies.

A diagnostic EIA for detection of the prevalent SRSV strain in United Kingdom outbreaks of gastroenteritis

Small round structured viruses (SRSVs) are the major cause of outbreaks of gastroenteritis in the UK. Diagnosis is problematic due to insensitive electron microscopy (EM) or technically demanding reverse transcription polymerase chain reaction (RT-PCR) techniques. We have studied outbreaks of non-bacterial gastroenteritis using an EIA based upon recombinant capsid protein from the currently prevalent circulating strain of SRSV (Lordsdale Genotype II) and compared its performance against EM and RT-PCR assays. Faecal specimens sent to the Bristol Public Health Laboratory for outbreak investigation from December 1996 to December 1997 were applied retrospectively to the SRSV EIA and results compared with the routine EM and RT-PCR that had been carried out prospectively. Overall, the three tests identified SRSVs in specimens from 70% of the outbreaks (213/305) investigated. Of the 213 total positive outbreaks, the EIA identified 71%, that compared favourably with EM (63%) and RT-PCR (84%). The Lordsdale Genotype II SRSV EIA provides a simple cost-effective assay that will for the first time make detection of currently circulating SRSV strains associated with UK outbreaks available to all routine laboratories. The EIA format makes the assay widely applicable to non-specialist laboratories, unlike the RT-PCR assay, and the improved sensitivity over EM will allow successful screening of UK outbreaks alongside commercial EIAs currently available for adenovirus, astrovirus and rotavirus. Furthermore, the assay will allow rapid identification of emerging SRSV strains.

Human caliciviruses in acute gastroenteritis of young children in the community

Episodes of acute gastroenteritis in prospectively followed children between 2 months and 2 years of age were examined for rotaviruses, enteric adenoviruses, astroviruses, and human caliciviruses, including both Norwalk-like viruses (NLVs) and Sapporo-like viruses (SLVs), using PCR and reverse transcription (RT)-PCR assays. A virus was identified in 60% (502/832) of all episodes and in 85% of the moderately severe or severe episodes. Human caliciviruses were as common as rotaviruses, both being detected in 29% of the cases. NLVs accounted for a 20% etiologic share of all cases; the clinical picture was a moderately severe disease with vomiting as a predominant symptom. SLVs were detected in 9% of the cases, the clinical picture being a mild diarrheal disease. Astroviruses were found in 10% and enteric adenoviruses in 6% of the cases. Diagnosis with PCR and RT-PCR methods increases the detection of all gastroenteritis viruses, particularly human caliciviruses. As a group, human caliciviruses are common causative agents of gastroenteritis in children <2 years of age in Finland, and, of these, NLVs cause more severe disease than SLVs.

Genetic classification of "Norwalk-like viruses

Reverse transcription-polymerase chain reaction has been used worldwide for the diagnosis of Norwalk-like virus (NLV) infection, yet a commonly accepted genetic classification scheme has not been established. Amino acid sequences from four regions of open-reading frame 2 (ORF2) were used to analyze 101 NLV strains, including 2 bovine strains. On the basis of this analysis, a genetic classification scheme is proposed that differentiates 99 human strains into 2 major genetic groups consisting of 5 and 10 genetic clusters, respectively. The 2 bovine strains constitute a newly defined third major genetic group composed of 2 putative clusters represented by each strain. This classification scheme is well supported by the analysis of the entire ORF2 sequences from 38 strains selected to represent the genetic diversity of the human strains used above. This scheme should provide a firm scientific basis for the unified classification of NLV strains detected around the world.

Molecular detection and epidemiology of Sapporo-like viruses

Sapporo-like viruses (SLVs) are associated with acute gastroenteritis in humans. Due to a limited supply of available reagents for diagnosis, little is known about the incidence and pathogenicity of these viruses. We have developed a first-generation generic reverse transcriptase (RT) PCR assay based on a single primer pair targeting the RNA polymerase gene. With this assay, 55 (93%) of the 59 stool specimens collected in a 10-year period of time (1988 to 1998) and containing typical caliciviruses by electron microscopy tested positive and could be confirmed by Southern hybridization. By phylogenetic analysis, most SLV strains could be classified into one of the three recently described genotypes. However, three samples clustered separately, forming a potential new genotype. We sequenced the complete capsid gene of one of the strains in this cluster: Hu/SLV/Stockholm/97/SE. Alignment of the capsid sequences showed 40 to 74% amino acid identity among strains of the different clusters. Phylogenetic analysis of the aligned sequences confirmed the placing of Hu/SLV/Stockholm/97/SE into a new distinct genetic cluster. This is the first report on the development of a broadly reactive RT-PCR assay for the detection of SLVs.