Viral gastroenteritis in Europe: a new norovirus variant?

First norovirus outbreaks associated with consumption of green seaweed (Enteromorpha spp.) in South Korea

In February 2012, an outbreak of gastroenteritis was reported in school A; a successive outbreak was reported at school B. A retrospective cohort study conducted in school A showed that seasoned green seaweed with radishes (relative risk 7·9, 95% confidence interval 1·1-56·2) was significantly associated with illness. Similarly, a case-control study of students at school B showed that cases were 5·1 (95% confidence interval 1·1-24·8) times more likely to have eaten seasoned green seaweed with pears. Multiple norovirus genotypes were detected in samples from students in schools A and B. Norovirus GII.6 isolated from schools A and B were phylogenetically indistinguishable. Green seaweed was supplied by company X, and norovirus GII.4 was isolated from samples of green seaweed. Green seaweed was assumed to be linked to these outbreaks. To our knowledge, this is the first reported norovirus outbreak associated with green seaweed.

Evaluation of the Bioline Standard Diagnostics SD immunochromatographic norovirus detection kit using fecal specimens from Australian gastroenteritis incidents

Human norovirus is a major cause of both sporadic cases and outbreaks of gastroenteritis and comprises two main genogroups (GI and GII) which, in turn, comprise a variety of genotypes. The current study examined the efficacy of the Bioline SD kit using fecal material from Australian gastroenteritis incidents. At best, the SD kit had a sensitivity of 62%. Freezing and thawing specimens before testing significantly improved sensitivity. The SD kit had a specificity of 98.6%. Genotype analysis (Open Reading Frame 2) indicated the SD kit could detect a range of genotypes and genotype variants including GI.1, GI.3, GI.4, GII.1, GII.3, GII.4 (unclassified), GII.4 (2006b), GII.4 (2009), GII.4 (2012) and GII.6 but the kit failed to detect GI.2 and GII.2 norovirus. The kit did not cross-react with a number of common fecal viruses including astrovirus, sapovirus, rotavirus or adenovirus. The kit was very easy to use and would be valuable in point-of-care testing.

Evaluation of the RIDA(®)QUICK immunochromatographic norovirus detection assay using specimens from Australian gastroenteritis incidents

A range of laboratory methods is now available for the detection of norovirus, a major cause of gastroenteritis. Recently, a commercial immunochromatographic assay for norovirus detection, the RIDA(®)QUICK assay, has become available, but there is still only limited information on its efficacy. This study examined the sensitivity and specificity of the RIDA(®)QUICK assay, using faecal material received for testing in a major diagnostic/reference laboratory in Australia. The sensitivity of the assay was found to be 83% and the specificity was 100%. No false positive norovirus results were found and the assay did not cross-react with common faecal viruses such as rotavirus, astrovirus, sapovirus and adenovirus. The assay was less reliable for genogroup I (GI) noroviruses than for genogroup II (GII) noroviruses. Genotypes detected by the assay included GII.1, GII.2, GII.3, GII.4, GII.6 and GII.7. The assay failed to detect any GI specimens in the test group. Genotypes not detected included GI.4 and GI.6. The assay was simple and quick to perform. It is valuable in a point-of-care situation or as a backup in a laboratory where a rapid initial norovirus result is required.

Molecular changes associated with altered patterns of norovirus outbreak epidemics in Victoria, Australia, in 2006 to 2007

Noroviruses (NoVs) are now considered the most common cause of outbreaks of nonbacterial gastroenteritis, but the factors which control the incidence of NoVs are poorly understood. In 2006, the pattern of NoV outbreak epidemics in Victoria, Australia, changed compared to the pattern for 2002 to 2005 and 2007. This study examined molecular correlates of the changed NoV periodicity. For the period of 2002 to 2007, 8,507 fecal specimens from 1,495 gastroenteritis outbreaks were tested for NoV by reverse transcription-PCR, and 1,018 NoV outbreaks were identified. Nucleotide sequence analysis was used to define genotypes and GII.4 variants. For 2002 to 2007, GII.4 was the predominant genotype. For the period of 2002 to 2005 and 2007, a single NoV outbreak epidemic occurred in warmer months of each year, but in 2006 two epidemics occurred in 1 year, one in colder months and one in warmer months of the year. For 2002 to 2007, four major GII.4 variants, "2002 Oxford/Farmington Hills," "2004 Hunter," "2006a," and "2006b," were identified. Each NoV outbreak epidemic was linked principally to one of these four variants, and there was a time link, a delay of 2 to 6 months, between the first detection of a GII.4 variant and the first outbreak epidemic in which it was the principal variant. The unusual 2006 pattern of outbreak epidemics can then be correlated with the appearance of two GII.4 variants within a short space of time, resulting in two outbreak epidemics in a short space of time, i.e., in the 1 year. This study provides a potentially greater ability to predict the characteristics of NoV epidemics.

Inhibition of norovirus replication by morpholino oligomers targeting the 5'-end of the genome

Noroviruses are an important cause of non-bacterial epidemic gastroenteritis, but no specific antiviral therapies are available. We investigated the inhibitory effect of phosphorodiamidiate morpholino oligomers (PMOs) targeted against norovirus sequences. A panel of peptide-conjugated PMOs (PPMOs) specific for the murine norovirus (MNV) genome was developed, and two PPMO compounds directed against the first AUG of the ORF1 coding sequence near the 5'-end of the genome proved effective in inhibiting MNV replication in cells. A consensus PPMO (designated Noro 1.1), designed to target the corresponding region of several diverse human norovirus genotypes, decreased the efficiency of protein translation in a cell-free luciferase reporter assay and inhibited Norwalk virus protein expression in replicon-bearing cells. Our data suggest that PPMOs directed against the relatively conserved 5'-end of the norovirus genome may show broad antiviral activity against this genetically diverse group of viruses.

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

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

Real-time reverse transcription PCR detection of norovirus, sapovirus and astrovirus as causative agents of acute viral gastroenteritis

The design and development of highly sensitive real-time reverse transcription PCR assays for the detection of norovirus genogroups I, II and IV, sapovirus genogroups I, II and IV, and human astrovirus from stool samples is described. Examination of 140 stool samples from paediatric patients exhibiting symptoms of diarrhoea and/or vomiting resulted in increased detection levels as compared to examination by electron microscopy. Real-time PCR resulted in a 200% increase in the rate of detection of norovirus as compared to electron microscopy. Only genogroup II noroviruses were detected in the stool specimens and when examined using partial-genotyping primers all were identified as clustering with the genogroup II/4(Bristol/Lordsdale) cluster. Sapovirus was not detected in any of the stool specimens by electron microscopy while 11% (15/140) of specimens were sapovirus positive by real-time RT-PCR, accounting for 36% of calicivirus diarrhoea. Real-time RT-PCR resulted in a tenfold increase in the rate of detection of astrovirus when compared to detection by electron microscopy with both type 1 and type 4 human astroviruses being detected in circulation. The results highlight the importance of the introduction of molecular methods for the routine screening of stool samples for causative agents of viral gastroenteritis.

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

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

Changing distribution of norovirus genotypes and genetic analysis of recombinant GIIb among infants and children with diarrhea in Japan

A total of 402 fecal specimens collected during July 2003-June 2004 from infants and children with acute gastroenteritis, encompassing five localities (Maizuru, Tokyo, Sapporo, Saga, and Osaka) of Japan, were tested for the presence of norovirus by RT-PCR. It was found that 58 (14.4%) fecal specimens were positive for norovirus. Norovirus infection was detected throughout the year with the highest prevalence in December. Norovirus GII was the most predominant genogroup (98.3%; 57 of 58). The genotypes detected in this study were GI/4, GII/2, GII/3, GII/4, and GII/6. Of these, NoV GII/3 (known as the Arg320 virus cluster) was the most predominant genotype (43.9%), followed by NoV GII/4 (the Lordsdale virus cluster; 35.1%) and others. Two norovirus strains clustered with a "new variant designated GIIb" and a "new variant of GII/4" were found circulating in Japan for the first time. It was interesting to note that NoV GIIb and NoV GII/3 appeared to be the recombinant strains and the recombination site was demonstrated at the overlap of ORF1 and ORF2. The majority (96%) of the dominant norovirus strains were identified as the recombination of GII/3 capsid and GII/12 polymerase. The recombination in the NoV GIIb capsid gene at the breakpoint located at P1 domain was also identified. Obviously, NoV GIIb isolate in Japan had double recombination. This is the first report demonstrating the existence of different "new variants" co-circulating in Japanese infants and children with acute gastroenteritis.