Etiologic agents of acute gastroenteritis among Japanese infants and children: virus diversity and genetic analysis of sapovirus

The analysis of the genotype of Sapovirus outbreaks in Zhejiang Province

BACKGROUND

Sapovirus (SaV) infection is increasing globally. Concurrently, several SaV-outbreaks were observed in children of Zhejiang province, China, in recent years, In this study, the genotypes of Sapovirus from seven outbreaks in the Zhejiang province were analysed.

METHODS

A total of 105 faecal samples were collected from children aged between 4 and 17 years from the Zhejiang Provincial Center for Disease Control and Prevention between October 2021 and February 2023. Genotypes were processed using reverse transcription polymerase chain reaction and Sanger sequencing, while next-generation sequencing was used to generate a complete viral genome. Deduced amino acid sequences were analysed to detect VP1 gene mutations.

RESULTS

In total, 60 SaV-positive patients were detected at a 57.14% (60/105) positivity rate. Positive rates in the seven outbreaks were: 22.22% (2/9), 15.00% (3/20), 93.10% (27/29), 84.21% (16/19), 28.57% (2/7), 53.33% (8/15) and 33.33% (2/6), respectively. Four genotypes were identified in the seven outbreaks, of which, GI.1 accounted for 14.29% (1/7), GI.2 accounted for 14.29% (1/7), GI.6 and GII.5 accounted for 14.29% (1/7), and GI.6 accounted for 57.14% (4/7). All patients were children and outbreaks predominantly occurred in primary schools and during cold seasons. Additionally, the complete sequence from the GI.6 outbreak strain showed high homology (identity: 99.99%) with few common substitutions (Y300S, N302S and L8M) in VP1 protein.

CONCLUSIONS

SaV genotype diversity was observed in the seven outbreaks, with GI.6 being the main SaV genotype in Zhejiang province. It demonstrated high homology and may provide a platform for SaV prevention and control measures.

Detection and characterization of human astrovirus and sapovirus in outpatients with acute gastroenteritis in Guangzhou, China

Background

Human astrovirus (HAstV) and sapovirus (SaV) are common pathogens that can cause acute gastroenteritis (AGE). However, very few studies have reported the molecular epidemiology and clinical information on HAstV and SaV in China. This study aims to determine the molecular epidemiology and clinical features of HAstV and SaV in patients with AGE in Guangzhou, China.

Methods

For this study, 656 patients with AGE were enrolled. Their stool samples were screened for 15 enteropathogens using Luminex xTAG^® Gastrointestinal Pathogen Panel. HAstV and SaV were detected through an in-house multiplex reverse transcriptase polymerase chain reaction followed by phylogenetic analysis. We described and compared clinical features of AGE in patients with HAstV and SaV.

Results

Of the 656 stool samples, 63.72% (418/656) were found to be positive, with 550 enteropathogens (296 bacteria and 254 viruses). HAstV and SaV were detected in 20 (3.0%) and 12 (1.8%) samples, respectively. Four genotypes (genotypes 1, 2, 3, and 8) of HAstV and three genotypes (GI.1, GI.2 and GIV) of SaV were identified. Coinfection was observed in ten HAstV-positive and two SaV-positive samples. HAstV was more likely to occur in winter, while SaV in early spring. The median age of the patients with single HAstV infection was higher than that of the patients with other viruses (rotavirus, norovirus, and enteric adenovirus; P = 0.0476) and unknown etiology (P = 0.006). Coinfection with HAstV or SaV were not associated with disease severity (P > 0.05).

Conclusion

HAstV and SaV are the common causes of AGE in Guangzhou, China.

Global molecular prevalence and genotype distribution of Sapovirus in children with gastrointestinal complications: A systematic review and meta-analysis

Sapovirus (SaV) is an emerging cause of children gastrointestinal complications such as acute gastroenteritis (AGE). The aim of the present systematic review and meta-analysis was to estimate the global prevalence of the SaV in children and association of infection with SaVs and AGE in children based on case-control studies. Four international databases (PubMed, Scopus, Web of Sciences and Google Scholar) were used to retrieve English-language studies published between January 2000 and December 2020. Comprehensive Meta-Analysis software was applied to estimate the overall prevalence, publication bias and heterogeneity index. The pooled prevalence of SaV infection among children with gastroenteritis was 3.4% [95% confidence interval (CI): 2.9%-3.9%] based on a random-effects meta-analysis. Genogroup I was the dominant genogroup of SaV in children with gastroenteritis [2.2% (95% CI: 1.6%-3.0%)], association analysis showed that SaV was associated with gastroenteritis [OR: 1.843 (95% CI: 1.27-2.66)]. Given the significant prevalence of the virus in children, it is necessary to pay more attention to this situation. Therefore, preventive health measures in children should be a priority.

Diversity of human sapovirus genotypes detected in Japanese pediatric patients with acute gastroenteritis, 2014-2017

Sapovirus (SaV) is one of the pathogens related to acute gastroenteritis (AGE) in adults and children worldwide. This study reported the diversity of SaV genotypes in children with AGE in Japan from July 2014 to June 2017. Of a total of 2259 stool samples tested by using reverse transcription-PCR method and further analyzed by nucleotide sequencing, 114 (5.0%) were positive for SaV and GI.1 (83.3%) was the most predominant genotype, followed by GII.1, GIV.1, GI.2, GI.3, and GII.3 genotypes. Monthly distribution analysis demonstrated two epidemic peaks from July to December 2015 and February to May 2017. However, no detection peak was observed in 2014 and 2016. Phylogenetic analysis of the complete VP1 nucleotide sequences of these GI.1 strains revealed two major clusters of GI.1 and each of which contained GI.1 strains of both 2015 and 2017. This study suggests that the continuous surveillance of SaV is needed to monitor high genetic diversity in Japanese children with AGE.

Norovirus Outbreak Surveillance, China, 2016-2018

CaliciNet China, a network of provincial, county, and city laboratories coordinated by the Chinese Centers for Disease Control and Prevention, was launched in October 2016 to monitor the epidemiology and genotype distribution of norovirus outbreaks in China. During October 2016–September 2018, a total of 556 norovirus outbreaks were reported, and positive fecal samples from 470 (84.5%) outbreaks were genotyped. Most of these outbreaks were associated with person-to-person transmission (95.1%), occurred in childcare centers or schools (78.2%), and were reported during November–March of each year (63.5%). During the 2-year study period, 81.2% of all norovirus outbreaks were typed as GII.2[P16]. In China, most norovirus outbreaks are reported by childcare centers or schools; GII.2[P16] is the predominant genotype. Ongoing surveillance by CaliciNet China will provide information about the evolving norovirus genotype distribution and outbreak characteristics important for the development of effective interventions, including vaccines.

Differences in Illness Severity among Circulating Norovirus Genotypes in a Large Pediatric Cohort with Acute Gastroenteritis

Norovirus is a major pathogen identified in children with acute gastroenteritis (AGE), little is known about the strain's diversity and their clinical severity. Stool and/or rectal swabs were collected from children ≤18 years of age recruited at emergency departments (ED), and a provincial nursing advice phone line due to AGE symptoms in the province of Alberta, Canada between December 2014 and August 2018. Specimens were tested using a reverse transcription real time PCR and genotyped by Sanger sequencing. The Modified Vesikari Scale score (MVS) was used to evaluate the disease severity. The objectives are to identify the Genogroup and Genotype distribution and to compare illness severity between the GI and GII genogroups and to complete further analyses comparing the GII genotypes identified. GII.4 was the genotype most commonly identified. Children with GII.4 had higher MVS scores (12.0 (10.0, 14.0; p = 0.002)) and more prolonged diarrheal (5 days (3.0, 7.8)) and vomiting (3.2 days (1.7, 5.3; p < 0.001)) durations compared to other non GII.4 strains. The predominant strain varied by year with GII.4 Sydney[P31] predominant in 2014/15, GII.4 Sydney[P16] in 2015/16 and 2017/18, and GII.3[P12] in 2016/17. Genogroup II norovirus strains predominated in children with AGE with variance between years; clinical severity associated with different strains varied with episodes being most severe among GII.4 infected children.

The incidence of medically-attended norovirus gastro-enteritis in Japan: Modelling using a medical care insurance claims database

Background

The burden of medically-attended acute gastro-enteritis (MA-AGE) that can be attributed to norovirus is not well established in Japan. Using a nationwide database of medical care insurance claims, we estimated the incidence of medically-attended norovirus-attributable gastroenteritis (MA-NGE) in Japan.

Methods

The incidences of MA-NGE outpatient consultations or hospitalization in Japan were modelled on seasonal patterns of MA-AGE for unspecified causes derived from the Japan Medical Data Center (JMDC) database for the period July 2007 to June 2015.

Results

Mean age-adjusted annual incidence rates (per 10,000 person-years) of MA-NGE associated with outpatient care or hospitalization were 389 (95% CI 269–558) and 13 (95% CI 9–20), respectively. Highest rates were in children under 5 years of age: 1,569 (95% CI 1,325–1,792) for outpatient consultations and 48 (95% CI 39–56) for hospitalizations. Of all gastroenteritis episodes associated with outpatient care or hospitalization, 29% and 31% were attributed to norovirus, respectively. Norovirus was estimated to be responsible for 4,964,000 outpatient visits (95% CI 3,435,000–7,123,000) and 171,000 hospitalizations (95% CI 110,000–251,000) per year across Japan.

Conclusions

Incidence rates of MA-AGE are high in Japan, and norovirus-attributable disease is at least as high as in some other developed countries.

Epidemiology of gastroenteritis viruses in Japan: Prevalence, seasonality, and outbreak

Acute gastroenteritis has been recognized as one of the most common diseases in humans and continues to be a major public health problem worldwide. Several groups of viruses have been reported as the causative agents of acute gastroenteritis, including rotavirus, norovirus, sapovirus, human astrovirus, adenovirus, and an increasing number of others which have been reported more recently. The epidemiology, prevalence, seasonality, and outbreaks of these viruses have been reviewed in a number of studies conducted in Japan over three decades. Rotavirus and norovirus were the two most common viruses detected almost equally in children under 5 years of age who were suffering from acute gastroenteritis. Like many other countries, the main rotavirus strains circulating in pediatric patients in Japan are G1P[8], G2P[4], G3P[8], and G9P[8]. Norovirus GII.4 was involved in most outbreaks in Japan and found to be associated with the emergence of new variants Sydney_2012. The classic human astrovirus, MLB, and VA clades astroviruses were also commonly found in pediatric patients with acute diarrhea. The sapovirus and adenovirus have been identified as the minor viral causative agents for acute gastroenteritis in Japan.

Comprehensive review of human sapoviruses

Sapoviruses cause acute gastroenteritis in humans and animals. They belong to the genus Sapovirus within the family Caliciviridae. They infect and cause disease in humans of all ages, in both sporadic cases and outbreaks. The clinical symptoms of sapovirus gastroenteritis are indistinguishable from those caused by noroviruses, so laboratory diagnosis is essential to identify the pathogen. Sapoviruses are highly diverse genetically and antigenically. Currently, reverse transcription-PCR (RT-PCR) assays are widely used for sapovirus detection from clinical specimens due to their high sensitivity and broad reactivity as well as the lack of sensitive assays for antigen detection or cell culture systems for the detection of infectious viruses. Sapoviruses were first discovered in 1976 by electron microscopy in diarrheic samples of humans. To date, sapoviruses have also been detected from several animals: pigs, mink, dogs, sea lions, and bats. In this review, we focus on genomic and antigenic features, molecular typing/classification, detection methods, and clinical and epidemiological profiles of human sapoviruses.

Emerging and re-emerging virus infections in neonates and young pediatric patients

The epidemiology of virus infections has changed dramatically in Europe in recent years due to ecologic, anthropologic and biologic factors such as: i) climate modifications, ii) global exchange of goods and international travel, iii) increased immigration flux from Africa, South America, the Middle East and Asia, iv) reduction of cultivated areas, and v) emergence and re-emergence of human viruses from zoonotic reservoirs. In addition, recent technical advancements have allowed the identification of previously unrecognized autochthonous viral species. Thus, at present, the technical and cultural challenge is to recognize infections caused by viruses not normally circulating in our geographical region (both as imported cases or potential local outbreaks), sustained by recently discovered autochthonous viruses or due to recognized viruses which are no longer widespread in Western Europe due to past vaccination campaigns.

Novel intergenotype human norovirus recombinant GII.16/GII.3 in Bangladesh

Noroviruses (NoVs) are one of the major etiological agents of acute gastroenteritis in all age groups. In this study, we identified an intergenotype NoV recombinant strain in the fecal specimens of two male infants with acute diarrhea in Bangladesh. Phylogenetic analysis showed that the identified strains were recombinant NoV strains with a GII.3 capsid and a GII.16 polymerase gene. The recombination breakpoint was located in the ORF1/ORF2 overlap region. To the best of our knowledge this is the first report of a NoV recombinant GII.16/GII.3 strain worldwide.

Comparative evolution of GII.3 and GII.4 norovirus over a 31-year period

Noroviruses are the most common cause of epidemic gastroenteritis. Genotype II.3 is one of the most frequently detected noroviruses associated with sporadic infections. We studied the evolution of the major capsid gene from seven archival GII.3 noroviruses collected during a cross-sectional study at the Children's Hospital in Washington, DC, from 1975 through 1991, together with capsid sequence from 56 strains available in GenBank. Evolutionary analysis concluded that GII.3 viruses evolved at a rate of 4.16 × 10(-3) nucleotide substitutions/site/year (strict clock), which is similar to that described for the more prevalent GII.4 noroviruses. The analysis of the amino acid changes over the 31-year period found that GII.3 viruses evolve at a relatively steady state, maintaining 4% distance, and have a tendency to revert back to previously used residues while preserving the same carbohydrate binding profile. In contrast, GII.4 viruses demonstrate increasing rates of distance over time because of the continued integration of new amino acids and changing HBGA binding patterns. In GII.3 strains, seven sites acting under positive selection were predicted to be surface-exposed residues in the P2 domain, in contrast to GII.4 positively selected sites located primarily in the shell domain. Our study suggests that GII.3 noroviruses caused disease as early as 1975 and that they evolve via a specific pattern, responding to selective pressures induced by the host rather than presenting a nucleotide evolution rate lower than that of GII.4 noroviruses, as previously proposed. Understanding the evolutionary dynamics of prevalent noroviruses is relevant to the development of effective prevention and control strategies.

Molecular detection of genogroup I sapovirus in Tunisian children suffering from acute gastroenteritis

This study investigated the prevalence of sapovirus infections in children with acute gastroenteritis in Monastir region, Tunisia, from January 2003 to April 2007. Sapovirus was characterized by sequence and phylogenetic analyses of the partial polymerase gene. From 788 fecal specimens tested, 6 (0.8%) were positive for sapovirus, of these, 4 (66.7%) were monoinfections. All sapovirus positive samples were detected in outpatient, contrary to norovirus which was significantly more frequent in hospitalized children than in outpatients (14.5 vs. 9.5%, P = 0.03). The mean age of children with sapovirus infections was 11 ± 5.56 months (range 6-19 months). Sapovirus isolates were detected in March and between September and December 2003. Fever, vomiting, abdominal pain, and dehydration were not observed in patients with sapovirus infections. Analysis of nucleotide and amino acid sequences revealed that all 6 Tunisian sapovirus strains clustered in the GGI/1 genotype and strains were identical in the region sequenced, sharing 90.2% nucleotide identity with the reference strain Sapporo/82/JP (U65427). This represents the first finding of sapovirus infections in North Africa and especially in Tunisia. The data indicate that, contrary to norovirus which can cause severe diarrhea and is an important etiologic agent in hospitalized cases, sapovirus causes mild gastroenteritis in Tunisian children.

Rapid evolution of pandemic noroviruses of the GII.4 lineage

Over the last fifteen years there have been five pandemics of norovirus (NoV) associated gastroenteritis, and the period of stasis between each pandemic has been progressively shortening. NoV is classified into five genogroups, which can be further classified into 25 or more different human NoV genotypes; however, only one, genogroup II genotype 4 (GII.4), is associated with pandemics. Hence, GII.4 viruses have both a higher frequency in the host population and greater epidemiological fitness. The aim of this study was to investigate if the accuracy and rate of replication are contributing to the increased epidemiological fitness of the GII.4 strains. The replication and mutation rates were determined using in vitro RNA dependent RNA polymerase (RdRp) assays, and rates of evolution were determined by bioinformatics. GII.4 strains were compared to the second most reported genotype, recombinant GII.b/GII.3, the rarely detected GII.3 and GII.7 and as a control, hepatitis C virus (HCV). The predominant GII.4 strains had a higher mutation rate and rate of evolution compared to the less frequently detected GII.b, GII.3 and GII.7 strains. Furthermore, the GII.4 lineage had on average a 1.7-fold higher rate of evolution within the capsid sequence and a greater number of non-synonymous changes compared to other NoVs, supporting the theory that it is undergoing antigenic drift at a faster rate. Interestingly, the non-synonymous mutations for all three NoV genotypes were localised to common structural residues in the capsid, indicating that these sites are likely to be under immune selection. This study supports the hypothesis that the ability of the virus to generate genetic diversity is vital for viral fitness.

Since 1995, norovirus has caused five pandemics of acute gastroenteritis. These pandemics spread across the globe within a few months, causing great economic burden on society due to medical and social expenses. Norovirus, like influenza virus, has over 40 genotypes circulating within the population at the same time. However, it is only a single genotype, known as genogroup II genotype 4 (GII.4), that causes mass outbreaks and pandemics. Very little research has been conducted to determine why GII.4 viruses can cause pandemics. Consequently, we compared the evolution properties of several pandemic GII.4 strains to non-pandemic strains and found that the GII.4 viruses were undergoing evolution at a much higher rate than the non-pandemic norovirus strains. This phenomenon is similar to influenza virus, where an increase in antigenic drift has been associated with increased outbreaks. This discovery has important implications in understanding norovirus incidence and also the development of a vaccine and treatment for norovirus.

Molecular epidemiology of human astrovirus and adenovirus serotypes 40/41 strains related to acute diarrhea in Tunisian children

Human astrovirus (AstV) and adenovirus types 40 and 41 (AdV 40/41) are responsible for epidemic and endemic acute gastroenteritis in children and adults. The present study was designed to evaluate the prevalence and genetic diversity of enteric viruses in children in Tunisia. A total of 788 fecal samples were collected during a 4-year period in the region of Monastir, from children under 12 years old, hospitalized or presenting in dispensaries with symptoms of acute gastroenteritis. AstV and AdV40/41 were detected by immunoenzymatic methods and confirmed by PCR/RT-PCR and sequence analysis. Phylogenetic analyses were performed for nucleotide homology with reference strains. AstV and AdV40/41 were characterized as a causative agent in 28 (3.6%) and 18 (2.3%) of the fecal samples, respectively. Phylogenetic analysis showed that the AstVs belonged to the serotypes 3 (n = 4; 14.3%) and 1 (n = 24; 85.7%), and the enteric AdVs to the serotypes 40 (n = 1; 5.6%) and 41 (n = 17; 94.4%). This is the first report that describes the molecular epidemiology of AstV and AdV40/41 in Tunisian children. Their respective detection rate was very low, far below that of rotavirus and norovirus. The genetic diversity among these two viruses is relatively limited and varies depending on the area.

Acute gastroenteritis caused by multiple enteric pathogens in children

Of 303 children hospitalized with acute non-bloody, non-mucoid diarrhoea, 69 (22·8%) had polymicrobial infection, including 52 (17·2%) multiple viral infection and 17 (5·6%) viral and bacterial co-infection. Rotavirus had the most important role in both categories; thus the control of rotavirus infection is crucial for maintaining children's health in Taiwan.

Human caliciviruses in symptomatic and asymptomatic infections in children in Vellore, South India

Pediatric gastroenteritis is a major cause of childhood morbidity and mortality worldwide, especially in developing countries. It has been increasingly recognised that human caliciviruses (HuCV), comprising noroviruses (NoV), and sapoviruses (SaV), are important in both outbreak and non-outbreak settings. This study aimed to characterise caliciviruses detected in the faeces of hospitalized children and children in the community in India. This study examined 350 faecal samples from children presenting to the hospital with acute gastroenteritis and 673 samples collected from children in the community, 500 from children with diarrhea, and 173 samples from children without diarrhea. Strain characterisation was performed by reverse transcription-polymerase chain reaction (RT-PCR) and partial sequencing of the gene encoding the RNA-dependent RNA polymerase (RdRp) and/or a region spanning the open reading frames (ORFs) 1 and 2 (ORF1/ORF2) junction. A total of 68 of 350 specimens (19.4%) from hospitalized children were positive, and SaV and NoV accounted for 5.1 and 15.1% of the infections, respectively. Mixed infections of HuCVs with other enteric pathogens were seen in 9.4% of the total children tested. Sixty-eight out of 673 (10.1%) samples collected from children in the community were positive for caliciviruses, and SaV and NoV accounted for 3.4 and 6.6% of the infections. In the community cohort 55/500 (11%) and 13/173 (7.5%) were from symptomatic and asymptomatic children, respectively, and SaVs accounted for 17/500 (3.4%) and NoVs for 38/500 (7.6%) of the symptomatic infections. This is the first report of genotyping of circulating caliciviruses in both hospital and community in India and has increased the evidence for the role of these viruses in pediatric gastroenteritis in India.

Molecular epidemiology and clinical manifestations of viral gastroenteritis in hospitalized pediatric patients in Northern Taiwan

By reverse transcription-PCR or PCR, among 257 children with nonbacterial acute gastroenteritis (AGE), rotavirus, norovirus, astrovirus, enteric adenovirus, and multiple viruses were identified in 78 (30.4%), 21 (8.2%), 7 (2.7%), 51 (19.8%), and 53 (20.6%) patients, respectively. Higher disease severity was found for AGE caused by multiple viruses and by rotavirus alone. The majority of rotaviruses isolated from 2004 to 2006 belonged to genotypes G1 (20.4%), G2 (16.5%), G3 (27.2%), and G9 (21.4%).

Emergence of rare sapovirus genotype among infants and children with acute gastroenteritis in Japan

A total of 1,154 fecal specimens from infants and children with acute gastroenteritis in five cities in Japan (Maizuru, Tokyo, Sapporo, Saga, and Osaka), collected from July 2003 to June 2005, were tested for the presence of diarrheal viruses by reverse transcriptase multiplex PCR. Overall, 469 of 1,154 (40.6%) were positive for diarrheal viruses, of which 49 (10.4%) were positive for sapovirus. The peak of sapovirus infection shifted from April-June in 2003-2004 to October-December in 2004-2005. The observations show that maximum sapovirus prevalence can occur during warmer seasons. Sapovirus was subjected to molecular genetic analysis by sequencing. The results indicated that sapovirus genogroup I was a dominant group (100%). Sapovirus strains detected in this study were further classified into four genotypes (GI/1, GI/4, GI/6, and GI/8). Of these, sapovirus GI/1 was the most predominant, followed by sapovirus GI/6; these accounted for 93% (13 of 14) and 7% (1 of 14), respectively, in 2003-2004. However, it was noteworthy that sapovirus GI/6 suddenly emerged to become the leading genotype, accounting for 77% (27 of 35) of isolates in 2004-2005. This is believed to be the first report of the changing distribution of sapovirus genotypes and of the emergence of the rare sapovirus GI/6.

Prevalence of sapovirus infection among infants and children with acute gastroenteritis in Dhaka City, Bangladesh during 2004–2005

Sapovirus, a member of the family Caliciviridae is one of the major causative agents of viral gastroenteritis affecting all age group. Sapovirus was detected in 25 of 917 stool specimens from infants and children with acute gastroenteritis in a Children Hospital in Dhaka City, Bangladesh during 2004-2005. All fecal specimens were examined for sapovirus by reverse transcription-polymerase chain reaction. Molecular analysis of sapovirus was carried out by sequencing methods. Sapovirus detected in this study was clustered into only one distinct genogroup I. Sapovirus GI/1 was predominant, followed by GI/2 and accounted for 92% (23 of 25) and 8% (2 of 25), respectively. The results clearly indicated that sapovirus infections were observed most commonly in the autumn to winter seasons (September to January) in Dhaka City. The common clinical symptoms of sapovirus infected patients were dehydration (88%), vomiting (76%), and abdominal pain (60%). This is the first report of sapovirus in Bangladesh.

Outbreak of sapovirus infection among infants and children with acute gastroenteritis in Osaka City, Japan during 2004-2005

One hundred and twenty five fecal specimens were collected from sporadic cases of acute gastroenteritis in a pediatric clinic in Osaka City, Japan from July 2004 to June 2005 and tested for the presence of rotavirus, norovirus, sapovirus, astrovirus, and adenovirus by RT-multiplex PCR. Among diarrheal viruses detected, norovirus was the most prevalent (19.2%, 24 of 125), followed by group A rotavirus (18.4%, 23 of 125), astrovirus (1.6%, 2 of 125), and adenovirus (0.8%, 1 of 125), respectively. Interestingly, sapovirus infection was identified with high incidence of 17.6% (22 of 125). Sapovirus was subjected to molecular genetic analysis by sequencing. It was found that sapovirus detected in this study was classified into four genotypes (GI/1, GI/4, GI/6, and GI/8), and sapovirus GI/6 was predominant, followed by GI/8 and accounted for 81.8% (18 of 22) and 9.1% (2 of 22), respectively. It was noteworthy that sapovirus GI/6 infection was apparently confined within the period of 5 months (August 2004 through December 2004). This pattern of infection implied the outbreak of sapovirus GI/6 in these patients, which was the first outbreak of acute gastroenteritis attributed to sapovirus in Osaka City. Another interesting feature of the study was the appearance of two novel, naturally occurring recombinant sapoviruses circulating in the Japanese population studied. This report confirmed the presence as well as the importance of sapovirus causing acute gastroenteritis among Japanese infants and children.

Identification of sapovirus infection among Japanese infants in a day care center

A total of 921 fecal specimens collected from 44 infants in a day care center in Tokyo, Japan during June 1999 to July 2000 were tested for the presence of sapovirus by reverse transcription-polymerase chain reaction (RT-PCR). Of 88 fecal specimens from infants with acute gastroenteritis, 2.3% (2) were found to be positive for sapovirus. Twenty-two of 833 (2.6%) fecal specimens collected from asymptomatic infants were also infected with this virus. Another interesting feature was the demonstration of high incidence of sapovirus infection (95.5%, 21 of 22) identified in a single day care center, which was not due to viral shedding after the latest acute gastroenteritis. Sapovirus was subjected to genetic analysis by sequencing. Up to 4 of 24 sapoviruses (16.7%) were clustered into genogroup IV known as a rare group. Remarkably, majority (79.2%, 19 of 24) of sapovirus isolates detected in this study turned out to present one novel sapovirus genotype tentatively called GI/8. It was noteworthy to point out that the GI/8 sapovirus infection was apparently confined only within the period of 9 weeks (44th through 52nd weeks). This pattern of infection implied the outbreak of asymptomatic GI/8 sapovirus infection in these subjects. The findings clearly indicate genogroup I sapovirus can be classified into eight genotypes. This is the first report to underscore that sapovirus pathogen causes not only clinical manifestations of acute gastroenteritis but also asymptomatic infection in infants in day care centers in Japan.