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During the COVID-19 pandemic in 2021, Japan experienced an outbreak of respiratory syncytial virus (RSV) infection. A total of 51 RSV cases were detected from the infant specimens, including 38 rhinorrhea and 13 nasopharyngeal swabs, collected at the Tokyo Metropolitan Institute of Public Health. Of these 51 cases, 12 belonged to RSV-A and 39 to RSV-B. G protein gene sequences of RSV-A belonged to the ON1 genotype, whereas RSV-B belonged to the BA9 genotype; thus, different types of RSV were detected during the same period, suggesting that the unusual 2021 RSV season was not due to a single strain or genotype. Of all RSV-positive cases, the proportion of cases aged ≥2 years was 56.8% in 2021, which was higher than 31.2% in the past 5 years. This indicates that infants aged1 year who were originally susceptible to RSV infection were less likely to be infected with RSV because of the COVID-19 control measures. The 2021 epidemic peaked in the 28th week, which was 9 weeks earlier than the average from 2016 to 2020. It seems necessary to accumulate and analyze further data, such as factors that became an outbreak and the characteristics of the detected viruses in 2021.

Suppression of SARS-COV-2 based on the pH of a GO dispersion is reported. At higher pH of GO, the overall surface charge of the GO dispersion is more negative and with a large number of OH functional groups shows better SARS-CoV-2 inactivation.

The emergence of the Omicron variant of SARS-CoV-2 is an urgent global health concern1. In this study, our statistical modelling suggests that Omicron has spread more rapidly than the Delta variant in several countries including South Africa. Cell culture experiments showed Omicron to be less fusogenic than Delta and than an ancestral strain of SARS-CoV-2. Although the spike (S) protein of Delta is efficiently cleaved into two subunits, which facilitates cell–cell fusion2,3, the Omicron S protein was less efficiently cleaved compared to the S proteins of Delta and ancestral SARS-CoV-2. Furthermore, in a hamster model, Omicron showed decreased lung infectivity and was less pathogenic compared to Delta and ancestral SARS-CoV-2. Our multiscale investigations reveal the virological characteristics of Omicron, including rapid growth in the human population, lower fusogenicity and attenuated pathogenicity.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can be detected in the stool samples of patients with coronavirus disease 2019 (COVID-19), and this virus can be transmitted via the oral-fecal route. However, there are only few reports on the viral load in the stool samples. In this pilot study, we aimed to evaluate the clinical characteristics and viral load of SARS-CoV-2 in the stool samples of 13 patients with confirmed COVID-19 using pepper mild mottle virus as a control, which has been proposed as a potential marker of human feces contamination in the environmental water bodies. SARS-CoV-2 RNA was detected in the stool samples of four patients (31%), and among them, three exhibited symptoms of diarrhea. One patient who suffered from long-term diarrhea (22 days) exhibited highest level of viral RNA in the stool sample (8.28 log10 copies/g). However, we could not harvest SARS-CoV-2 from the stool sample of any patient, even after culturing with VeroE6/TMPRESS2 cells for four weeks. Our results suggest that SARS-CoV-2 RNA can be detected in the stool samples of patients with COVID-19 suffering from diarrhea. However, further studies elucidating the relationship between SARS-CoV-2 viral load in the stool samples and symptoms of diarrhea in large cohorts and upon adjusting other causative factors and virus infectivity are still warranted.

Correction for ‘SARS-CoV-2 suppression depending on the pH of graphene oxide nanosheets’ by Md. Saidul Islam et al., Nanoscale Adv., 2023, https://doi.org/10.1039/D3NA00084B.

The genetic characterization of archival specimens is important for evaluating the evolutionary processes of noroviruses. Complete viral genome sequences, GVIII.1[GII.P28] and GIX.1[GII.P15], were determined from two archival specimens collected in Tokyo, Japan, in 1986 and 1995. In addition, complete VP1 and partial RdRp sequences of four samples collected between 1975 and 1983 were determined. Two viruses were classified as GI.5[P5] and GI.9[P9]; however, the viruses from the other two samples could not be assigned to any known genotypes using norovirus typing tools and phylogenetic analysis, suggesting that they might be untypable genotypes. Further evolutionary analysis of these viruses is warranted.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants have received increasing attention globally because of their increased transmissibility and potential to escape immunity. Although whole-genome sequencing is the gold standard method for SARS-CoV-2 mutation detection and lineage determination, it is costly and time-consuming. However, SARS-CoV-2 variants can be identified based on select variant-specific single nucleotide polymorphisms (SNPs) in the spike protein-encoding gene (S). This study validated and compared the limit of detection (LOD) of L452R, N501Y, HV69/70 del and E484K as variant-specific SNPs of the S gene and RdRP as a SARS-CoV-2-specific gene, using the Novaplex SARS-CoV-2 variants assay kit series. For three SARS-CoV-2 lineages (B.1.617.2, B.1.1.7 and R.1), one strain per lineage was used. Variant-specific SNPs of the S gene were analysed using the Novaplex SARS-CoV-2 variants I assay and Novaplex SARS-CoV-2 variants II assay kits. Validation confirmed the LODs of the variant kits. The LOD for each target variant-specific SNP and RdRP was five RNA copies per reaction. The Novaplex SARS-CoV-2 variants assay kit series performs well and the LOD for SARS-CoV-2 detection and variant-specific SNP detection are consistent. The kits are suitable for use as routine laboratory tests for SARS-CoV-2 and variant-specific SNP detection in a single step, saving time and labour.

Saliva sample can be self-collected and used in testing of SARS-CoV-2 nucleic acid amplification tests (NAATs) test in Japan. However, this may have difficulty collecting a proper specimen when collecting for the first time. We compared 2 collection methods, conventional methods and Direct Saliva Sample Collection method (DiSC) from 44 asymptomatic or symptomatic individuals who were in quarantine in Toho university hospital. RT-PCR by DiSC method showed about 70 % positive percent agreement compared to RT-PCR by conventional methods. In addition, comparing RT-PCR and TMA by DiSC method, TMA showed about 90 % positive percent agreement compared to RT-PCR. DiSC method is easy to perform by every person, does not have complicated restrictions/instructions and can be used in RT-PCR and TMA. This method allows for ease of saliva collection in certain patient populations.

Soon after the emergence and global spread of the SARS-CoV-2 Omicron lineage BA.1, another Omicron lineage, BA.2, began outcompeting BA.1. The results of statistical analysis showed that the effective reproduction number of BA.2 is 1.4-fold higher than that of BA.1. Neutralization experiments revealed that immunity induced by COVID vaccines widely administered to human populations is not effective against BA.2, similar to BA.1, and that the antigenicity of BA.2 is notably different from that of BA.1. Cell culture experiments showed that the BA.2 spike confers higher replication efficacy in human nasal epithelial cells and is more efficient in mediating syncytia formation than the BA.1 spike. Furthermore, infection experiments using hamsters indicated that the BA.2 spike-bearing virus is more pathogenic than the BA.1 spike-bearing virus. Altogether, the results of our multiscale investigations suggest that the risk of BA.2 to global health is potentially higher than that of BA.1.

There were five epidemic waves of coronavirus disease 2019 in Japan between 2020 and 2021. It remains unclear how the domestic waves arose and abated. To better understand this, we analyzed the pangenomic sequences of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and characterized the molecular epidemiological features of the five epidemic waves in Japan. In this study, we performed deep sequencing to determine the pangenomic SARS-CoV-2 sequences of 1,286 samples collected in two cities far from each other, Tokyo Metropolis and Nagoya. Then, the spatiotemporal genetic changes of the obtained sequences were compared with the sequences available in the Global Initiative on Sharing All Influenza Data (GISAID) database. A total of 873 genotypes carrying different sets of mutations were identified in the five epidemic waves. Phylogenetic analysis demonstrated that sharp displacements of lineages and genotypes occurred between consecutive waves over the 2 years. In addition, a wide variety of genotypes were observed in the early half of each wave, whereas a few genotypes were detected across Japan during an entire wave. Phylogenetically, putative descendant genotypes observed late in each wave displayed regional clustering and evolution in Japan. The genetic diversity of SARS-CoV-2 displayed uneven dynamics during each epidemic wave in Japan. Our findings provide an important molecular epidemiological basis to aid in controlling future SARS-CoV-2 epidemics.

Introduction The Tokyo Metropolitan Government (TMG) conducted an external quality assessment (EQA) survey of pathogen nucleic acid amplification tests (NAATs) as a TMG EQA program for SARS-CoV-2 for clinical laboratories in Tokyo. Methods We diluted and prepared a standard product manufactured by Company A to about 2,500 copies/mL to make a positive control and distribute it with a negative control. The participants reported the use of the NAATs methods for SARS-CoV-2, the name of the real-time RT-PCR kit, the name of the detection device, the target gene(s), nucleic acid extraction kit, Threshold Cycle value in the case of RT-PCR and the Threshold time value and Differential calculation value in the case of Loop-Mediated Isothermal Amplification (LAMP) method. Results As a result, 17 laboratories using fully automated equipment and 34 laboratories using the RT-PCR method reported generally appropriate results in this EQA survey. On the other hand, among the laboratories that adopted the LAMP method, there were a plurality of laboratories that judged positive samples to be negative. Conclusion The false negative result is considered to be due to the fact that the amount of virus genome contained in the quality control reagent used this time was below the detection limit of the LAMP method combined with the rapid extraction reagent for influenza virus. On the other hand, false positive results are considered to be due to the non-specific reaction of the NAATs. The EQA program must be continued for the proper implementation of the pathogen NAATs.

After the global spread of the SARS-CoV-2 Omicron BA.2, some BA.2 subvariants, including BA.2.9.1, BA.2.11, BA.2.12.1, BA.4, and BA.5, emerged in multiple countries. Our statistical analysis showed that the effective reproduction numbers of these BA.2 subvariants are greater than that of the original BA.2. Neutralization experiments revealed that the immunity induced by BA.1/2 infections is less effective against BA.4/5. Cell culture experiments showed that BA.2.12.1 and BA.4/5 replicate more efficiently in human alveolar epithelial cells than BA.2, and particularly, BA.4/5 is more fusogenic than BA.2. We further provided the structure of the BA.4/5 spike receptor-binding domain that binds to human ACE2 and considered how the substitutions in the BA.4/5 spike play roles in ACE2 binding and immune evasion. Moreover, experiments using hamsters suggested that BA.4/5 is more pathogenic than BA.2. Our multiscale investigations suggest that the risk of BA.2 subvariants, particularly BA.4/5, to global health is greater than that of original BA.2.

SummaryDuring the current SARS-CoV-2 pandemic, a variety of mutations have been accumulated in the viral genome, and at least five variants of concerns (VOCs) have been considered as the hazardous SARS-CoV-2 variants to the human society. The newly emerging VOC, the B.1.617.2 lineage (delta variant), closely associates with a huge COVID-19 surge in India in Spring 2021. However, its virological property remains unclear. Here, we show that the B.1.617 variants are highly fusogenic and form prominent syncytia. Bioinformatic analyses reveal that the P681R mutation in the spike protein is highly conserved in this lineage. Although the P681R mutation decreases viral infectivity, this mutation confers the neutralizing antibody resistance. Notably, we demonstrate that the P681R mutation facilitates the furin-mediated spike cleavage and enhances and accelerates cell-cell fusion. Our data suggest that the P681R mutation is a hallmark characterizing the virological phenotype of this newest VOC, which may associate with viral pathogenicity.HighlightsP681R mutation is highly conserved in the B.1.617 lineagesP681R mutation accelerates and enhances SARS-CoV-2 S-mediated fusionPromotion of viral fusion by P681R mutation is augmented by TMPRSS2

Recently, we experienced an outbreak of acute hepatitis A virus (HAV) infection between 2018 and 2020. Herein, we describe this male-dominant HAV infection outbreak observed among non-human immunodeficiency virus (HIV)-infected persons in the northern part of Tokyo, Japan. Clinical information was collected from patient interviews and from medical record descriptions. In the present study, 21 patients were retrospectively analyzed. A total of 90.4 and 33.3% of patients were males, and men who have sex with men (MSM), respectively. The total bilirubin levels and platelet counts tended to be lower in the MSM group than in the non-MSM group. C-reactive protein (CRP) levels tended to be higher in acute liver failure (ALF) patients than in non-ALF patients. Prolonged cholestasis was observed in one patient (4.8%). We also found that 18 HAV isolates belonged to HAV subgenotype IA/subgroup 13 (S13), which clustered with the HAV isolate (KX151459) that was derived from an outbreak of HAV infection among MSM in Taiwan in 2015. Our results suggest that the application of antivirals against HAV, as well as HAV vaccines, would be useful for the treatment and prevention of severe HAV infection.

Monoclonal antibody therapy is a promising option for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, and a cocktail of antibodies (REGN-COV) has been administered to infected patients with a favorable outcome. However, it is necessary to continue generating novel sets of monoclonal antibodies with neutralizing activity because viral variants can emerge that show resistance to the currently utilized antibodies. Here, we isolated a new cocktail of antibodies, EV053273 and EV053286, from peripheral blood mononuclear cells derived from convalescent patients infected with wild-type SARS-CoV-2. EV053273 exerted potent antiviral activity against the Wuhan wild-type virus as well as the Alpha and Delta variants in vitro, whereas the antiviral activity of EV053286 was moderate, but it had a wide-range of suppressive activity on the wild-type virus as well as the Alpha, Beta, Delta, Kappa, Omicron BA.1, and BA.2 variants. With the combined use of EV053273 and EV053286, we observed similar inhibitory effects on viral replication as with REGN-COV in vitro. We further assessed their activity in vivo by using a mouse model infected with a recently established viral strain with adopted infectious activity in mice. Independent experiments revealed that the combined use of EV053273 and EV053286 or the single use of each monoclonal antibody efficiently blocked infection in vivo. Together with data showing that these two monoclonal antibodies could neutralize REGN-COV escape variants and the Omicron variant, our findings suggest that the EV053273 and EV053286 monoclonal antibody cocktail is a novel clinically applicable therapeutic candidate for SARS-CoV-2 infection.

Highlights • SARS-CoV-2 RNA can be detected in patients’ specimens. • The duration and severity of SARS-CoV-2 viral shedding in the urine is currently unknown. • We identified continuous viral shedding in the urine of a severe COVID-19 patient. • Careful handling of urine samples from patients with COVID-19 is recommended.

Background Amebiasis, which is caused by Entamoeba histolytica, is a re-emerging public health issue owing to sexually transmitted infection (STI) in Japan. However, epidemiological data are quite limited. Methods To reveal the relative prevalence of sexually transmitted E. histolytica infection to other STIs, we conducted a cross-sectional study at a voluntary counselling and testing (VCT) centre in Tokyo. Seroprevalence of E. histolytica was assessed according to positivity with an ELISA for E. histolytica-specific IgG in serum samples collected from anonymous VCT clients. Results Among 2083 samples, seropositive rate for E. histolytica was 2.64%, which was higher than that for HIV-1 (0.34%, p

BackgroundAmebiasis, which is caused byEntamoeba histolytica, is a re-emerging public health issue owing to sexually transmitted infection (STI) in Japan. However, epidemiological data are quite limited.MethodsTo reveal the relative prevalence of sexually transmittedE. histolyticainfection to other STIs, we conducted a cross-sectional study at a voluntary counselling and testing (VCT) centre in Tokyo. Seroprevalence ofE. histolyticawas assessed according to positivity with an ELISA forE. histolytica-specific IgG in serum samples collected from anonymous VCT clients.ResultsAmong 2083 samples, seropositive rate forE. histolyticawas 2.64%, which was higher than that for HIV-1 (0.34%, pChlamydia trachomatisin urine by transcription-mediated amplification (TMA) was 4.59%. Seropositivity forE. histolyticawas high among RPR/Treponema pallidumhemagglutination (TPHA)-positive individuals and it was not different between clients with and without other STIs. Both seropositivity ofE. histolyticaand RPR were high among male clients. The seropositive rate for anti-E. histolyticaantibody was positively correlated with age. TMA positivity for urineC. trachomatiswas high among female clients and negatively correlated with age. Regression analysis identified that male sex, older age and TPHA-positive results are independent risk factors ofE. histolyticaseropositivity.ConclusionsSeroprevalence ofE. histolyticawas 7.9 times higher than that of HIV-1 at a VCT centre in Tokyo, with a tendency to be higher among people at risk for syphilis infection. There is a need for education and specific interventions against this parasite, as a potentially re-emerging pathogen.

The first step of the UNAIDS/WHO 90-90-90 targets to encourage early diagnosis with treatment for the control of HIV-1 epidemic is to achieve 90% HIV-1 diagnosis in infected individuals. In Japan, approximately 30% of newly reported cases have been annually identified by AIDS onset, implying that substantial numbers of HIV-1-infected individuals remain undiagnosed. However, the proportion of undiagnosed cases has not yet been determined. In the present study, the proportion of recent HIV-1 infections to newly-diagnosed cases was determined from 2006 to 2015 using a recent infection assay for three metropolitan areas in Japan: Tokyo, Osaka, and Fukuoka. Estimated median periods between infection and diagnosis were 1.0, 1.8, and 2.9 years for Tokyo, Osaka, and Fukuoka, respectively. Estimation of annual HIV-1 incidence by a back-calculation method using these data as well as HIV/AIDS national surveillance data indicated proportions of undiagnosed to new HIV-1 infections from 2006 to 2015 to be 18% in Tokyo, 22% in Osaka, 38% in Fukuoka, and 28% in Japan. This is the first report estimating HIV-1 incidence in Japan using a serological biomarker in combination with national HIV/AIDS surveillance data.

BackgroundAmebiasis, which is caused byEntamoeba histolytica, is a re-emerging public health issue owing to sexually transmitted infection (STI) in Japan. However, epidemiological data are quite limited.MethodologyTo reveal the relative prevalence of sexually transmittedE. histolyticainfection to other STIs, we conducted a cross-sectional study at a voluntary counselling and testing (VCT) centre in Tokyo. Seroprevalence ofE. histolyticawas assessed according to positivity with an enzyme-linked immunosorbent assay forE. histolytica-specific IgG in serum samples collected from anonymous VCT clients.Principal FindingsAmong 2,083 samples, seropositivity forE. histolyticawas 2.64%, which was higher than that for HIV-1 (0.34%, p < 0.001) and comparable to that for syphilis (rapid plasma reagin (RPR) 2.11%, p = 0.31). Positivity forChlamydia trachomatisin urine by transcription-mediated amplification (TMA) was 4.59%. Seropositivity forE. histolyticawas high among RPR-orTreponema pallidumhemagglutination (TPHA)-positive individuals and it was not different between clients with and without other STIs. Both seropositivity ofE. histolyticaand RPR were high among male clients. The seropositive rate for anti-E. histolyticaantibody was positively correlated with age. TMA positivity for urineC. trachomatiswas high among female clients and negatively correlated with age. Regression analysis identified that male sex, older age, and TPHA-positive results are independent risk factors ofE. histolyticaseropositivity.ConclusionsSeroprevalence ofE. histolyticawas 7.9 times higher than that of HIV-1 at a VCT centre in Tokyo, with a tendency to be higher among people at risk for syphilis infection.Author summaryAmebiasis caused byEntamoeba histolyticais an increasingly prevalent sexually transmitted infection (STI) in Japan; however, relative to other STIs, the prevalence ofE. histolyticahas not been fully assessed. We investigated the seropositivity ofE. histolyticausing serum samples from 2,083 clients of a voluntary counselling and testing centre in Tokyo.E. histolyticaseroprevalence (2.64%) was 7.9 times higher than that of HIV-1 (0.31%) and the same as that of syphilis (rapid plasma reagin: 2.11%). Logistic regression analysis showed thatE. histolyticaseroprevalence tended to be higher among individuals who were male, older, and positive inTreponema pallidumhemagglutination. These results strongly suggest that public health interventions should be considered to control sexual transmission ofE. histolyticainfection, which is currently neglected in Japan.

HIV-1 CRF01_AE and subtype B (B) have dominated and their different circulating recombinant forms (CRFs) have emerged in East and Southeast Asian countries. Here, we report a novel drug-resistant HIV-1 CRF. Five independent recombinant specimens exhibiting discordant subtype results for the gag, pol, and env sequences were isolated. These recombinants had the CRF01_AE (gag p17)/B (pol PR-RT and IN)/CRF01_AE (env C2-V3) pattern similar to CRF69_01B. Sequence analysis of four near full-length HIV-1 genomes revealed a unique phylogenetic cluster distinct from previously reported CRFs. Of the four recombinants, three shared an identical mosaic structure including seven breakpoints in the gag, pol, vif, and env regions, designated CRF76_01B. The one remaining recombinant had additional recombination breakpoints in the vpu region and exhibited another unique recombinant form composed of CRF76_01B and B. These findings provide important insight into the transmission dynamics of HIV-1 in Asia that may be important for its effective prevention.

Human-to-human transmission of PA I38 mutant influenza A(H3N2) viruses with reduced baloxavir susceptibility has been reported in Japan. In December 2019, we detected a PA E23K mutant A(H1N1)pdm09 virus from a child without baloxavir treatment. The PA E23K mutant virus exhibited reduced baloxavir susceptibility but remained susceptible to neuraminidase inhibitors. Epidemiological data suggest possible transmission of this PA E23K mutant virus among humans, although its growth capability relative to that of the wild-type virus was reduced. Therefore, baloxavir susceptibility monitoring of influenza viruses is essential.

The early diagnosis of human immunodeficiency virus (HIV) infection is important to provide effective antiviral treatment and to prevent transmission of HIV. One of the key issues to achieve this goal is to shorten the so-called "diagnostic window period" when the humoral immune response toward the virus is not fully developed during the acute phase of HIV-1 infection. In 2008, the Espline HIV Ag/Ab test kit (E4G, Fujirebio Inc. Japan) was marketed in Japan belonging to the fourth generation of HIV test kits characterized by its ability to detect both viral antigens (Ag) and anti-HIV-1/2 antibodies (Ab). E4G is the first and only fourth generation immunochromatographic HIV test kit approved in Japan at present. To evaluate its performance to diagnose acute HIV infection (AHI), E4G was compared with fourth generation Ag/Ab ELISA test kits, a third generation PA test kit, WB and real-time PCR for the testing of 25 AHI clinical specimens. E4G detected HIV infection in 18/25 specimens (sensitivity : 72.0%), of which the viral Ag was detected in only 2 specimens (8.0%) bearing a viral load > 10 million copies/mL. No spesimens were simultaneously reactive to both Ag and Ab against HIV. The third generation PA achieved a positive score of 17/ 25 specimens (68.0%), which was almost the same as the E4G figure. In contrast the fourth generation Ag/ Ab ELISA scored all the 25 AHI specimens positive (sensitivity : 100%). Overall, although having the merit of offering a rapid diagnostic test for HIV infection, E4G does not provide a sensitivity in AHI diagnosis superior to test kits currently available.

The emergence and transmission of drug-resistant human immunodeficiency virus-1 (HIV-1) compromises antiretroviral treatment for HIV-1. Thus, testing for drug resistance is recommended at diagnosis and before initiating highly active antiretroviral treatment. We conducted an epidemiological study enrolling newly diagnosed patients between 2003 and 2008 in our nationwide surveillance network. In the 6-year study period, the prevalence of drug-resistant HIV-1 among 2573 patients, consisting mainly of Japanese men in their late-30s and infected through male-to-male sexual contacts, followed an increasing trend from 5.9% (16/273) in 2003 to 8.3% (50/605) in 2008. Nucleoside reverse transcriptase inhibitor-associated mutations predominated in each year, with T215 revertants being the most abundant. The predictive factor for drug-resistant HIV-1 transmission was subtype B (OR=2.36; p=0.004), and those for recent HIV-1 infection were male gender (OR=3.79; p=0.009), MSM behavior (OR=1.67; p=0.01), Japanese nationality (OR=2.31; p=0.008), and subtype B (OR=5.64; p

Highly active antiretroviral therapy (HAART) can suppress human immunodeficiency virus type 1 (HIV-1) replication and plasma HIV-1 to below detectable levels. However, HAART becomes ineffective when drug-resistant viruses emerge during HAART. Monitoring drug-resistance mutations in viruses is necessary for selecting new drugs or therapies effective at inhibiting such HIV-1 variants. Most laboratories in Japan perform the tests using in-house protocols. However, the quality of these tests has never been assessed. Our study assessing the accuracy and reliability of HIV-1 genotypic drug-resistance testing in 15 laboratories in Japan revealed that the quality was very high (97.3% accurate). The errors, though rare, were caused by human errors, poor electropherograms, and the use of inadequate primers. Here, we propose troubleshooting procedures to improve testing accuracy and reliability in Japan.

An epidemic outbreak of both norovirus (NV) and astrovirus (ASV) occurred on a research ship surveying Tokyo Bay, causing acute gastroenteritis in 26 of its 37 crew members. The presence of viral pathogens in fecal specimens was analyzed, and noroviruses were identified by reverse transcription-PCR in 18 (48.6%) of these specimens. In addition, astroviruses were identified in 14 (37.8%) of the fecal samples from the affected crew members, and multiple viral infections of both NV and ASV were observed in 6 cases. The genogrouping of the NV-positive samples was then examined by dot blot hybridization, and it was determined that all of the isolates were from genogroup II (GII). No bacterial pathogens were subsequently isolated from fecal specimens. Furthermore, a variety of NV strains were identified by sequencing and single-stranded conformational polymorphism (SSCP) analyses of PCR products from the fecal samples. One recombinant NV isolate, Minato/14, was identified as a recombinant NV strain of GII/6 and GII/1. The other NV isolates from this outbreak were classified into three NV genotypes (GII/1 [Minato/10], GII/4 [Minato/33], and GII/5 [Minato/6]). Furthermore, ASVs in positive samples were determined to belong to serotypes 1 and 2 by sequencing analysis. Our findings thus indicate that coinfections with NV and ASV, including a number of NV genotypes, persisted during an outbreak of gastroenteritis in a closed environment.