Failure to detect norovirus in a large group of asymptomatic individuals

A semi-nested RT-PCR assay for detection of norovirus in rat fecal samples

Norovirus is a highly prevalent pathogen that can infect a wide range of host species. Thus far, there have only been two reports of norovirus infection in rats. Diagnostic assays for the detection of norovirus are well established, but a specific molecular assay for the diagnosis of norovirus infection in laboratory rats has not yet been reported. In this study, we describe the development of a sensitive, semi-nested RT-PCR assay for detection of norovirus in fecal samples from Rattus norvegicus, reared in animal facilities under different sanitary barrier conditions. Additionally, we describe the first report of the presence of norovirus in rat colonies from Brazilian animal facilities.

Global Prevalence of Asymptomatic Norovirus Infection: A Meta-analysis

BACKGROUND

Studies about asymptomatic norovirus infections have been frequently reported. We aim to assess the global prevalence of asymptomatic infections.

METHOD

We identified publications that included the proportion of asymptomatic norovirus infections by searching in PubMed, Ovid, Scopus, and Web of Science and by screening references from the articles reviewed. The principal summary data were the prevalence of asymptomatic norovirus infection. Random-effect models for meta-analysis were fitted to generate estimates of overall and subgroup prevalence.

FINDINGS

Of 81 studies included, asymptomatic norovirus prevalence was estimated at 7% (95% CI: 6%-9%). Africa, Meso America and South America had higher prevalence (15%, 14%, 11%, respectively) while the prevalence in Europe and North America was lower (4%). Prevalence was similar between community and hospital (9%). Prevalence was higher in children (8%) than adults (4%). For food handlers, prevalence was estimated at 3%. In context of outbreaks, prevalence estimated from 15 studies was as high as 18% (95% CI: 10%-30%).

INTERPRETATION

This knowledge could have an impact on the development of transmission prevention strategies in the future. The high prevalence indicated asymptomatic individuals must not be overlooked.

OUTSTANDING QUESTIONS

The high prevalence indicated asymptomatic individuals must not be overlooked. Asymptomatic individuals may play an important role in norovirus transmission. This knowledge could have an impact on the development of transmission prevention strategies.

A High Burden of Asymptomatic Gastrointestinal Infections in Traditional Communities in Papua New Guinea

Stool samples were collected from 148 healthy adults living a traditional subsistence lifestyle in Papua New Guinea and screened for enteric pathogens using real-time RT-PCR/PCR assays. Enteric pathogens were detected in a high proportion (41%) of individuals. Clear differences were observed in the detection of pathogens between highland and lowland communities. In particular, there was a marked difference in detection rates of norovirus GII (20% and 0%, respectively) and Shigella sp. (15% and 0%, respectively). Analysis of the relationship between enteric pathogen carriage and microbial community composition of participants, using box plots to compare specific normal flora population numbers, did not suggest that gut microbial composition was directly associated with pathogen carriage. This study suggests that enteric pathogens are common in healthy individuals in Papua New Guinean highland communities, presumably acting as a reservoir of infection and thus contributing to a high burden of gastrointestinal illnesses.

Reassuringly low carriage of enteropathogens among healthy Swedish children in day care centres

OBJECTIVES

Infectious gastroenteritis is one of the most common diseases among children and has a considerable impact on health and socio-economy. Day care centres are high-risk environments for infections. The aim of this study was to investigate if asymptomatic preschool children constitute a reservoir for potential enteropathogens.

STUDY DESIGN

In total, 438 individual diapers were collected from day care centres in Uppsala, Sweden, during spring and autumn, and molecular techniques were used to estimate the prevalence of asymptomatic carriage of multiple enteropathogens.

METHODS

Faecal samples were analysed with multiplex polymerase chain reaction (PCR) (xTAG^® Gastrointestinal Pathogen Panel; Luminex Corporation, Toronto, Canada) targeting 21 different pathogens. Samples with a median fluorescence intensity above threshold were re-analysed with a second PCR assay.

RESULTS

Sixteen of the 438 samples were positive for enteropathogens, 1.6% for enteric adenovirus, 0.7% for Campylobacter spp., and 0.7% for norovirus.

CONCLUSIONS

Preschool children in Uppsala constitute a limited reservoir for potential enteropathogens.

Norovirus prevention and the prevalence of asymptomatic norovirus infection in kindergartens and primary schools in Changzhou, China: Status of the knowledge, attitudes, behaviors, and requirements

BACKGROUND

We estimated the status of norovirus infection and prevention in kindergartens and primary schools and identified poor areas for which future education is needed. We evaluated the knowledge, attitude, behavior, requirements of outbreak prevention, and rate of asymptomatic carriers.

METHODS

Two self-administered questionnaires were conducted for data collection. Five hundred seventy-four teachers from kindergartens and primary schools and 3,114 students from primary schools in Changzhou city were sampled for questionnaire investigation. In addition, 511 rectal swabs from healthy children were taken for norovirus detection.

RESULTS

Twenty-one of 511 children were asymptomatically infected with norovirus. The rate of asymptomatic norovirus infection children in kindergartens was 2.7% and 4.7% in primary schools. Nineteen of 21 positive samples were GII strains, the other 2 were GI strains. In addition, we found that primary schools were less prepared to prevent norovirus outbreaks than kindergartens. Settings in the suburban counties needed more education on norovirus prevention.

CONCLUSIONS

The results of this study emphasize the need for training of primary schools and suburban schools about norovirus prevention. Asymptomatic norovirus infection should receive more attention.

The role of chronic norovirus infection in the enteropathy associated with common variable immunodeficiency

OBJECTIVES

A severe enteropathy of unknown etiology can be associated with common variable immunodeficiency (CVID).

METHODS

S tool and archived small intestinal mucosal biopsies from patients with CVID enteropathy were analyzed by PCR for the presence of Norovirus RNA. The PCR products were sequenced to determine the relationship of viral isolates. Stool samples from 10 patients with CVID but no enteropathy served as controls.

RESULTS

All eight patients in our CVID cohort with enteropathy showed persistent fecal excretion of Norovirus. Analysis of archived duodenal biopsies revealed a strong association between the presence of Norovirus and villous atrophy over a period of up to 8 years. Analysis of the viral isolates from each patient revealed distinct strains of genogroup II.4. Sequence analysis from consecutive biopsy specimens of one patient demonstrated persistence of the same viral strain over a 6-year period. CVID patients without enteropathy showed no evidence of Norovirus carriage. Viral clearance occurred spontaneously in one patient and followed oral Ribavirin therapy in two further patients, and resulted in complete symptomatic and histological recovery. However, Ribavirin treatment in two further patients was unsuccessful.

CONCLUSIONS

Norovirus is an important pathogen for patients with CVID and a cause of CVID enteropathy, as viral clearance, symptom resolution, and histological recovery coincide. Ribavirin requires further evaluation as a potential therapy.

The dynamics of norovirus outbreak epidemics: recent insights

Noroviruses are a major cause of gastroenteritis outbreaks worldwide. Norovirus outbreaks frequently occur as epidemics which appear to be related to both genetic and environmental factors. This review considers recent progress in understanding these factors. The norovirus genome undergoes continuous change and this appears to be important in the persistence of the virus in the community. Studies on the common GII.4 genotype have shown that some norovirus outbreak epidemics involving this genotype are correlated with specific changes in the genome. In contrast to the growing understanding of the role of genetic factors in norovirus outbreak epidemics, the role of environmental factors is less well understood. Topics reviewed here include long term excretion of norovirus in some individuals, long term survivability of norovirus in the environment, the role of meteorological factors in the control of norovirus outbreaks and the possible zoonotic transmission of the virus.

Risk factors for symptomatic and asymptomatic norovirus infection in the community

The objective of this study was to investigate risk factors for norovirus-associated infectious intestinal disease (IID) and asymptomatic norovirus infection. Individuals with IID and healthy controls were recruited in a community-based study in England (1993-1996). This is the first risk-factor study to use viral load measurements, generated by real-time RT-PCR, to identify cases of norovirus-associated IID and asymptomatic infections. Using multivariable logistic regression the main risk factor identified for norovirus-associated IID was contact with a person with IID symptoms. Infectious contacts accounted for 54% of norovirus cases in young children and 39% of norovirus cases in older children and adults. For young children, contacts outside the household presented the highest risk; for older children and adults, the highest risk was associated with child contacts inside the household. Foreign travel and consumption of shellfish increased the risk of norovirus-associated IID. Lifestyle and dietary factors were associated with a decreased risk of both norovirus-associated IID and asymptomatic infection. No risk factors were identified for asymptomatic norovirus infection.

Seasonal prevalence of asymptomatic norovirus infection in Korean children

The prevalence of asymptomatic norovirus (NoV) infection was investigated in children registered for kindergarten in Korea during the winter and summer. Children with no gastrointestinal symptoms, including diarrhea and abdominal pain, during the 2 weeks before and following sample collection were included in this investigation. NoV presence and genetic identification were determined with real-time reverse transcriptase-polymerase chain reaction and conventional nested reverse transcriptase-polymerase chain reaction. The prevalence of NoV in asymptomatic children was 5.5% in the winter and 3.5% in the summer, respectively. GII.4 was the most prevalent NoV genotype, but GII.2 and GI.10 were also found during genetic analysis. This study demonstrates that asymptomatic NoV infection may be an important source of transmission in kindergarten children.

Urticaria associated with Norovirus infection: report of two cases

Acute and chronic urticaria may be triggered by infection. Streptococci and Helicobacter pylori are the most frequent acute infectious causes. We present two cases in which we cultured Norovirus in the stool of patients with both acute and chronic urticaria. Noroviruses (genus Norovirus, family Caliciviridae) are a group of single stranded RNA, nonenveloped viruses which cause acute gastroenteritis in humans. Norovirus was recently approved as the official genus name for the group of viruses provisionally described as Norwalk-like viruses (NLV). Therapy is symptomatic. Noroviruses should be regarded as possible infectious trigger for dermatologic diseases. In seeking a focus of viral or bacterial infection for skin diseases with unknown origin, stool cultures should be part of the routine evaluation.

Continuous presence of noroviruses and sapoviruses in raw sewage reflects infections among inhabitants of Toyama, Japan (2006 to 2008)

Various genotypes of norovirus (NoV) (genogroup I genotype 1 [GI.1], -2, -4, -5, -8, -11, -12, and -14; GII.3, -4, -6, -7, -10, -13, -14, and -15), and sapovirus (SaV) (GI.1 and GI.2, GII.1, and GIV.1) were detected from raw sewage from April 2006 to March 2008, while limited numbers of genotypes of NoV (GI.8, GII.4, GII.6, and GII.13) and SaV (GII.3 and GIV.1) and of NoV (GII.4, GII.7, and GII.13) were detected from clinical cases and healthy children, respectively. During the winter 2006 to 2008, a large number of sporadic gastroenteritis outbreaks and many outbreaks caused by NoV GII.4 occurred among inhabitants in Toyama, Japan. The copy number of genomes of NoV GII detected from raw sewage changed in relation to the number of outbreaks. NoV strains of the same genotypes observed in both raw sewage and human specimens belonged to the same cluster by phylogenetic analysis and had almost identical nucleotide sequences among each genotype. These data suggest that NoVs and SaVs detected from raw sewage reflect the viruses circulating in the community, irrespective of symptoms, and that subclinical infections of NoV are common in Japan. Combined surveys of raw sewage with those of clinical cases help us to understand the relationship between infection of these viruses and gastroenteritis.

Human norovirus infection and the lessons from animal caliciviruses

PURPOSE OF REVIEW

Human noroviruses are a major cause of infectious intestinal disease, particularly in the health sector, with considerable knock-on effects on care provision through ward closures and staff sickness. This review will describe recent advances in our understanding of human noroviruses. In addition, we will consider related nonhuman caliciviruses to highlight some potential difficulties in the control of caliciviral disease.

RECENT FINDINGS

Using more sensitive reverse transcriptase polymerase chain reaction based assays, noroviruses are now recognized as the most common cause of infectious intestinal disease in the community, as well as outbreaks of the infectious intestinal disease. After recovery from acute disease, some individuals continue shedding norovirus, particularly if immunosuppressed. The noroviruses are extremely variable, which has important implications for protection following challenge, and for future vaccination. From amongst this variability, new strains have emerged with the potential to spread widely. Recently a mouse norovirus has been identified which will afford new insights into the biology of these important viruses. Studies on human susceptibility have identified some resistant individuals in the population and a potential virus receptor, which may lead to the development of novel antiviral therapies.

SUMMARY

Lack of cell culture systems for the human noroviruses is being overcome by molecular technologies. Such studies have provided new insight into the significance and epidemiology of these viruses and opened the possibility of disease control through vaccination. Work on nonhuman caliciviruses has interesting parallels with human noroviruses, and provides new insights into the understanding of these important human pathogens.