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In this study, we demonstrate that differences within the P2 domain of norovirus genogroup I (GI) strains can be used to segregate outbreaks which are unrelated, whereas complete conservation within this region allows tracking of strains that are part of a single outbreak and likely to have a common source.

Norovirus strains were detected in two patients and in environmental swabs from a pediatric primary immunodeficiency unit in London, United Kingdom, during an infection control incident in November and December 2007. Detailed analyses of the gene encoding the P2 domain demonstrated that the majority of the strains were not related to the patients and that the environmental contamination was most likely due to secondary transfer by the hands of staff or visitors.

Background: Norovirus (NoV) is commonly associated with gastrointestinal infection. It is normally transmitted person-to-person or from contaminated surfaces, although food-borne transmission is possible., Methods: We conducted environmental, epidemiological, and microbiological investigations to ascertain the route of transmission of two linked outbreaks of NoV associated with events where food was consumed. Multivariate logistic regression was used to determine food items independently associated with infection., Results: In outbreak A, 19 of the 26 people who completed the food questionnaire fulfilled the case definition. The highest relative risks (RR) were for chicken kebab (RR 3, 95% confidence interval (CI) 0.9-10.4), pork sausages (RR 2.1, 95% CI 0.5-9.1), pasta salad (RR 1.94, 95% CI 0.9-4.1), cheese (RR 1.6, 95% CI 0.9-2.8), and green leaf salad (RR 1.5, 95% CI 0.9-2.4). In outbreak B, 60 of the 106 people surveyed fulfilled the case definition. Green leaf salad (adjusted odds ratio (aOR) 3.2, 95% CI 1.4-9.9) and coleslaw (aOR 8.2, 95% CI 3-22.2) were independently associated with illness in the multivariate logistic regression model. NoV genogroup II genotype 6 (GII-6) was identified in cases of both outbreaks and a food handler who had prepared salads for both events., Conclusion: Because outbreak investigations of small cohorts may not yield epidemiological association to food, most of these outbreaks may be attributed to the person-to-person transmission route. Therefore ascertainment of food-borne NoV infection may be low, underestimating the true prevalence of this route of transmission.

The aim of this study was to apply sequence analysis of a hyper variable region of the norovirus (NoV) genome in order to identify point source outbreaks associated with suspect food or water. The hyper-variable region of the gene encoding the P2 domain was chosen as small differences in sequence are likely to indicate virus from different sources whereas identical sequence may reveal transmission routes and the source of contamination. Strains with 100% similarity were considered as originating from a common source, whereas, strains with one or more mutations in the hyper variable region sequenced were regarded as representing unrelated transmission events. This study was able to identify a point source outbreak of a dominant strain, GII-4, on a cruise ship but also of a less common strain, GII-2, between two schools. Also identical GII-3 strains were demonstrated in food handlers amongst the same outbreak; however epidemiologically related outbreaks showed different GII-3 strains indicating multiple sources of contamination., (Copyright 2009 Wiley-Liss, Inc.)

Background: Noroviruses (NoVs) are associated with outbreaks of diarrhoeal illness in hospitals, nursing and residential homes and other institutional settings. NoV strains exhibit wide genetic diversity, and different virus genogroups and genotypes co-circulate in any geographical region at the same time, although most outbreaks of gastroenteritis are predominantly associated with genogroup II. The reverse transcription-polymerase chain reaction (RT-PCR) is the gold standard for detecting NoVs in clinical samples., Objectives: This study evaluates commercialised Loopamp kits for detecting NoV GI and NoV GII in faecal samples collected from patients with gastroenteritis and compares the results with those obtained using real-time RT-PCR with NoV genogroup sequence-specific detection., Study Design: Five hundred and ten faecal samples collected from patients with gastroenteritis were evaluated for the presence of NoV using the gold-standard real-time RT-PCRs and the Loopamp assays., Results: The Loopamp Norovirus GI and GII detection kits performed well compared to genogroup-specific real-time RT-PCR. Although the sensitivity of detection of GI strains (83.3%) was less than that for GII strains (97.4%), this will have little impact on the laboratory diagnosis of NoV, since GII strains are associated with the majority of outbreaks examined., Conclusions: The Loopamp GII detection kit is a sensitive method for detecting all the commonly circulating GII-4 strains included in the evaluation panel.

Tracking the spread of noroviruses during outbreaks of gastroenteritis is hampered by the lack of sequence diversity in those regions of the genome chosen for virus detection and characterization. Sequence analysis of regions of the genes encoding the RNA-dependent RNA polymerase and the S domain of the capsid does not provide sufficient discrimination between genotypically related strains of different outbreaks. However, analysis of sequences derived from the region encoding the P2 domain showed 100% similarity among strains from the same outbreak and <100% similarity among strains of different outbreaks. The prolonged nature of some hospital outbreaks, links between hospitals, and the introduction of multiple strains of a single genotype associated with an outbreak aboard a cruise ship were determined using this method. This provides a powerful tool for tracking outbreak strains and the subsequent analysis and validation of interventions in a background of multiple introductions of virus strains of the same genotype or genetic cluster.

The incidence of calicivirus infection in Ghana and many other African countries is not known. Thirteen (15.9%) of the 82 diarrhoeic stool samples tested for caliciviruses were positive for noroviruses (NoVs). NoVs were present in all age groups and were detected only during the diarrhoea peak that coincided with the peak rotavirus season. Ten (76.9%) of the NoV detected were genogroup II (GII) NoVs and the remaining three (23.1%) genogroup I (GI) NoVs. The predominant GII detected was GII-4 (60%, 6/10). Three of the GII NoVs were determined to be recombinants of GII-8/GII-14 as deduced from the sequencing of the region spanning the Orf1/2 junction. The GII genotypes formed four clusters with published GII sequences. The data shown enhances understanding of NoV diversity in Ghanaian children and demonstrate the global spread of distinct common genotypes to African countries.

Background: Noroviruses are highly infectious pathogens that cause gastroenteritis in the community and in semi-closed institutions such as hospitals. During outbreaks, multiple units within a hospital are often affected, and a major question for control programs is: are the affected units part of the same outbreak or are they unrelated transmission events? In practice, investigators often assume a transmission link based on epidemiological observations, rather than a systematic approach to tracing transmission.Here, we present a combined molecular and statistical method for assessing:1) whether observed clusters provide evidence of local transmission and2) the probability that anecdotally|linked outbreaks truly shared a transmission event., Methods: 76 healthcare associated outbreaks were observed in an active and prospective surveillance scheme of 15 hospitals in the county of Avon, England from April 2002 to March 2003. Viral RNA from 64 out of 76 specimens from distinct outbreaks was amplified by reverse transcription-PCR and was sequenced in the polymerase (ORF 1) and capsid (ORF 2) regions. The genetic diversity, at the nucleotide level, was analysed in relation to the epidemiological patterns., Results: Two out of four genetic and epidemiological clusters of outbreaks were unlikely to have occurred by chance alone, thus suggesting local transmission. There was anecdotal epidemiological evidence of a transmission link among 5 outbreaks pairs. By combining this epidemiological observation with viral sequence data, the evidence of a link remained convincing in 3 of these pairs. These results are sensitive to prior beliefs of the strength of epidemiological evidence especially when the outbreak strains are common in the background population., Conclusion: The evidence suggests that transmission between hospitals units does occur. Using the proposed criteria, certain hypothesized transmission links between outbreaks were supported while others were refuted. The combined molecular/epidemiologic approach presented here could be applied to other viral populations and potentially to other pathogens for a more thorough view of transmission.

A fecal archive containing 115 sapovirus (SaV) strains detected in samples collected from 15 outbreaks and 98 sporadic cases of gastroenteritis between 1989 and 2004 in the UK were characterized in order to determine the genomic diversity within SaV co-circulating in the human population. Strains were characterized by partial sequencing of the genes encoding the RNA-dependent RNA polymerase (RdRp) region and/or the polymerase/capsid (Pol/Cap) junction of the open reading frame (Orf) 1. Overall, SaV of genogroup I genotype 1 (GI 1) were the predominant strains circulating in the UK in each year between 1989 and 2004. During 2004, GII 1 was the predominant strain. These two SaV types accounted for 89.5% of the sporadic cases and outbreaks in the UK. The remaining cases were caused by six other SaV genotypes. On the basis of partial sequencing of the RdRp and capsid encoding genes of strains, which did not show sufficient homology to any of the currently recognized genotypes, we propose the inclusion of a presumptive fourth genotype within genogroup I (GI 4)., (Copyright 2006 Wiley-Liss, Inc.)

The diversity of norovirus (NV) genotypes was investigated in persons who were ill with acute gastroenteritis associated with the consumption of oysters. Initial results from a commercial enzyme immunoassay (EIA) indicated a mixed NV genogroup I (GI) and II (GII) outbreak. A reverse-transcriptase (RT)-PCR for NVs was applied to nucleic acid extracted from faecal specimens collected from symptomatic cases. Using primers that amplified contiguous sequences in the ORF1/2 region of the NV genome and a hemi-nested PCR derived from this assay, three different GII and two GI NV genotypes were detected and the strains were characterised by DNA sequencing. Using this approach a recombinant NV genotype, rGII-3a (recombinant Harrow/Mexico) the predominant strain identified in several symptomatic cases from the outbreak, was detected and characterised. No other gastroenteric viruses, including rotavirus, astrovirus, sapovirus and adenovirus 40/41 were detected by RT-PCR and PCR.

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., (Copyright 2004 Wiley-Liss, Inc.)

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., (Copyright 2004 Wiley-Liss, Inc.)

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 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.

Background: Highly publicised outbreaks of norovirus gastroenteritis in hospitals in the UK and Ireland and cruise ships in the USA sparked speculation about whether this reported activity was unusual., Methods: We analysed data collected through a collaborative research and surveillance network of viral gastroenteritis in ten European countries (England and Wales were analysed as one region). We compiled data on total number of outbreaks by month, and compared genetic sequences from the isolated viruses. Data were compared with historic data from a systematic retrospective review of surveillance systems and with a central database of viral sequences., Findings: Three regions (England and Wales, Germany, and the Netherlands) had sustained epidemiological and viral characterisation data from 1995 to 2002. In all three, we noted a striking increase in norovirus outbreaks in 2002 that coincided with the detection and emergence of a new predominant norovirus variant of genogroup II4, which had a consistent mutation in the polymerase gene. Eight of nine regions had an annual peak in 2002 and the new genogroup II4 variant was detected in nine countries. Also, the detection of the new variant preceded an atypical spring and summer peak of outbreaks in three countries., Interpretation: Our data from ten European countries show a striking increase and unusual seasonal pattern of norovirus gastroenteritis in 2002 that occurred concurrently with the emergence of a novel genetic variant. In addition to showing the added value of an international network for viral gastroenteritis outbreaks, these observations raise questions about the biological properties of the variant and the mechanisms for its rapid dissemination.

Background: Noroviruses are the most common cause of gastroenteritis outbreaks in industrialised countries. Gastroenteritis caused by Norovirus infection has been described as a highly seasonal syndrome, often referred to as "winter vomiting disease"., Methods: The Public Health Laboratory Service Communicable Disease Surveillance Centre has systematically collected reports of laboratory confirmed cases of Norovirus-gastroenteritis since 1995. We analysed these data for annual and seasonal trends and age distribution., Results: A mid-summer peak in reported cases of Norovirus was observed in 2002, unlike all six previous years when there was a marked summer decline. Total reports from 2002 have also been higher than all previous years. From the first 10 months of 2002, a total of 3029 Norovirus diagnoses were reported compared the previous peak in 1996 of 2437 diagnoses for the whole 12-month period. The increase in 2002 was most marked in the 65 and older age group., Conclusion: This surveillance data challenges the view that Noroviruses infections exclusively have wintertime seasonality.