Typing of human astroviruses from clinical isolates by enzyme immunoassay and nucleotide sequencing

Development of a one step real-time RT-PCR method for sensitive detection of human astrovirus

Human astrovirus (HAstV) has been recognized as the second most common cause of diarrhoea among children under 5 years old. To date, the true incidence of HAstV was underestimated when using enzyme immunoabsorbent assays (EIAs) and conventional reverse transcription (RT)-polymerase chain reaction (PCR) methods. The sensitivity of detection of EIA is insufficient and, although RT-PCR is more sensitive than EIA, the time required is a limitation for astrovirus detection. The aim of the study was to develop a real-time RT-PCR method in order to increase the sensitivity, to quantify the viral load and to minimize the time required for HAstV detection. The real-time RT-PCR reported here requires only one rapid step to obtain a high sensitivity (0.0052 infectious units (IU) (0.0026 IU/microl)) in all human astrovirus detected. The real-time RT-PCR detected IUs down to a 10(-6) dilution with an improvement in the detection limit of factor 10(4), whereas the conventional RT-PCR detected down to IUs 10(-2) dilution. This process is able to reduce the time of the assay and avoids the risk of contamination. The method described below has been validated with a panel of 100 clinical samples and the results obtained confirmed the high specificity of the assay; consequently, the application of this assay for molecular diagnosis is feasible as a versatile tool for ascertaining the true implication of HAstV in acute viral gastroenteritis.

Environmental monitoring for gastroenteric viruses in a pediatric primary immunodeficiency unit

The aim of this study was to determine if gastroenteric viruses were present on surfaces and equipment in a pediatric primary immunodeficiency unit (PPIU) by environmental sampling using swabs and subsequent nucleic acid extraction and reverse transcriptase PCR assays. A PPIU was chosen, and 11 swabs were taken at the same sites every 2 weeks for 6 months. Nested/heminested PCR assays were used to screen for astroviruses (AsV), noroviruses (NoV), and rotaviruses (RV). AsV, NoV, and RV were detected at multiple swab sites during the study period. NoV was the most frequently detected virus on environmental surfaces; however, RV was detected on 79% and NoV on 50% of swabbing dates during the study period. Toilet taps were the most contaminated sites. Fecal samples from selected patients in the unit were also screened during the study period, and patients excreted AsV, NoV, and RV at times during the study. New cleaning schedules and changes in some of the PPIU sanitary furniture have been suggested as a means of reducing environmental contamination.

Molecular characterization of human astroviruses isolated in Brazil, including the complete sequences of astrovirus genotypes 4 and 5

Human astroviruses (HAstV) are recognized as an important cause of gastroenteritis in young children worldwide. This study describes the molecular characteristics of astroviruses isolated in Brazil, using RT-PCR and molecular sequencing of segments of all three viral ORFs. Genetic analysis of a 348-nucleotide segment from ORF 2 demonstrated that the Brazilian isolates belong to HAstV genotypes 1 to 5 and 8. ORF 1b sequences displayed a high degree of nucleotide identity even between different genotypes, which disfavours HAstV genotyping in this region. ORF 1a sequence analysis classified all Brazilian samples as genogroup A. The complete sequences of HAstV genotype 4 (putative serotype 4) and genotype 5 (putative serotype 5) were determined for the first time.

Astroviren und Toroviren

Neben den seit 10 Jahren als Gastroenteritiserreger identifizierten Astroviren und den vorbeschriebenen Noro-, Calici-, Adeno- und Rotaviren gibt es noch eine Reihe anderer Viren, die eher nebenbefundlich gastrointestinale Symptome auslösen können, wie HIV, CMV, Entero- und Herpesviren, von denen bisher noch nicht bekannt ist, ob sie, wie zumeist im Tierreich, vergleichbare Erkrankungen verursachen können. Zu diesen gehören die Corona- und Toroviren, Parvoviren und Picobirnaviren. Zumindest für Coronaviren und Picobirnaviren wurde in Einzelfällen eine Assoziation von Durchfallerkrankungen bei Neugeborenen und AIDS-Patienten beschrieben (Chang et al. 1982, Grohmann et al. 1993).

Coxsackievirus A1 wurde in Zusammenhang mit Durchfallerkrankungen gebracht, ohne dass dies allerdings bis heute bewiesen werden konnte (Townsend et al. 1982). Gleiches gilt auch für Reoviren und Toroviren (Koopmans et al. 1997).

Prevalence and genetic diversity of astroviruses in children with and without diarrhea in São Luís, Maranhão, Brazil

Human astroviruses (HAstV) have been increasingly identified as important etiological agents of acute gastroenteritis in children up to five years old. The aim of this study was to determine the prevalence and genotype diversity of HAstV in children with symptomatic and asymptomatic infections in São Luís, Maranhão, Brazil. From June 1997 to July 1999 a total of 183 fecal samples 84 from symptomatic and 99 from asymptomatic children were tested by enzyme immunoassay for HAstV. Prevalence rates were found to be 11 and 3% for symptomatic and asymptomatic children, respectively. Reverse transcription-polymerase chain reaction (RT-PCR) was carried out in 46 specimens (26 symptomatic and 20 asymptomatic) including the 12 samples that were positive by enzyme immunoassay (EIA). The overall positivity yielded by both methods was 8% (15/184); of these, 11% (9/84) for symptomatic and 5% (5/99) for those without symptoms or signs. Sequence analysis of amplicons revealed that HAstV-1 genotype was the most prevalent, accounting for 60% of isolates. Genotypes 2, 3, 4, and 5 were also detected, as one single isolate (10%) for each type. Variations in the sequences were observed when Brazilian isolates were compared to prototype strains identified in the United Kingdom. No seasonal pattern of occurrence was observed during these two years of study, and peak detection rate was observed in children aged between 3 and 6 months in the symptomatic group, and between 18 and 24 months in the controls.

Reverse transcriptase-PCR for the detection of Astrovirus in children with nosocomial acute diarrhoea in Naples, Italy

OBJECTIVE

This study was made to determine the incidence of nosocomial viral gastroenteritis in all children aged 0-4 years, admitted in the Pediatric Hospital over a 3-year period.

METHODS

Astrovirus was detected by reverse transcriptase-PCR; routine diagnostic tests for Rotavirus, Adenovirus, and common bacterial pathogens were carried out on all samples.

RESULTS

Of the 460 children with nosocomial diarrhea, 23 harbored Astrovirus (5%). Most cases occurred during the coldest months of the year. Children under 1 year of age were the most susceptible population.

CONCLUSION

The collected data confirms the importance of viral etiology in nosocomial gastroenteritis. The reported rate of detection stresses the importance of Astrovirus in pediatric diarrhea. The authors recommend screening for this virus on a routine basis.

Use of a heminested reverse transcriptase PCR assay for detection of astrovirus in environmental swabs from an outbreak of gastroenteritis in a pediatric primary immunodeficiency unit

An outbreak of astrovirus gastroenteritis occurred in the Primary Immunodeficiency Unit at Newcastle General Hospital in March 2004. Environmental swabbing of the unit was undertaken after the outbreak, with multiple sites swabbed pre- and postcleaning. Astroviruses were detected in four environmental swabs and from two patient fecal samples using heminested reverse transcriptase PCR. An astrovirus genotype 3 strain was identified in both environmental swabs and fecal specimens and was the strain identified as being responsible for the outbreak. Environmental transmission of the virus was thought to have occurred by contamination of a syringe pump outside the laminar-flow curtain of a patient who was admitted with astrovirus gastroenteritis. This was subsequently transmitted to a cubicle next door and to a television/games console in a parents' room in the ward. Environmental monitoring of surfaces/equipment, using PCR assays for gastroenteric viruses in hospital situations where infection can give rise to serious clinical complications, may have a role in controlling and monitoring cleaning and the subsequent prevention of nosocomial transmission of gastroenteritis.

Multiple norovirus genotypes characterised from an oyster-associated outbreak of gastroenteritis

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.

Human astrovirus diagnosis and typing: current and future prospects

Human astroviruses (HAstV) are important human pathogens causing gastroenteritis worldwide. The increased recognition of astroviruses as the cause of sporadic outbreaks of disease is due to the recent availability of improved diagnostic methods. During the last decade, most epidemiological surveys have chosen astrovirus-specific RT-PCR as screening methods. In addition to serotyping by molecular techniques, new typing methods are being developed that may also identify other viral properties related to virulence. The information provided by different typing assays is required for a better understanding of both the antigenic diversity and the molecular mechanisms of pathogenicity.

Identification of viral agents associated with diarrhea in young children during a winter season in Beijing, China

Background

Viral diarrhea remains a major cause of childhood morbidity and mortality worldwide. Although rotavirus was extensively studied in China, few comprehensive studies of all viral agents related to diarrhea in children have been conducted.

Objectives

Our study was performed to investigate the role of enteric viruses in acute diarrhea in our country and to evaluate methods that could be used in routine diagnostics.

Study design

One hundred stool samples were collected from children under 5 years of age seeking medical care for acute diarrhea during the winter season 2000/2001 in Beijing Children's Hospital. All specimens were initially screened microscopically for leucocytes/red blood cells. Samples with negative results were analyzed for virus presence using commercial EIAs and/or in-house RT-PCRs.

Results

At least one viral agent was found in 67% of the specimens. The frequency of rotavirus, astrovirus, norovirus and enteric adenovirus was 59%, 8%, 6% and 2%, respectively. Dual infections were found in 9.0% (6/67) of the positive samples. The results from rotavirus and astrovirus EIAs were concordant with those of rotavirus and astrovirus RT-PCRs.

Conclusions

Enteric viruses play an important role in pediatric diarrhea during the winter season in China. A combination of microscopic examination of stool samples with specific EIA assays to detect virus antigen in stool specimens may be suitable for routine diagnostics.

Application of a molecular panel to demonstrate enterotropic virus shedding by healthy and human immunodeficiency virus-infected patients

We used a molecular panel, targeting seven enteric viruses, to explore the advantage of using molecular methods to establish the etiology of enteric diseases and to evaluate the prevalence of enteric viruses in asymptomatic human immunodeficiency virus-infected patients. This approach favors rapidity and sensitivity of laboratory diagnosis of viral enteric syndromes.

Human astrovirus C-terminal nsP1a protein is involved in RNA replication

Human astrovirus nonstructural C-terminal nsP1a protein, which contains a hypervariable region (HVR) and colocalizes with the endoplasmic reticulum and viral RNA, has been suggested to be involved in the RNA replication process. Four viruses differing only in their C-terminal nsP1a protein, corresponding to HVR-derived genotypes IV, V, VI, and XII, were all able to replicate in CaCo-2 cells but displayed differences in their RNA replication and growth properties. Two overall patterns of replication were observed: types IV and V on one side, and types VI and XII on the other. The main detected differences were on the levels of antigenomic and subgenomic RNAs, being the latter significantly higher in types IV and V. Accordingly, quantification of viral RNA load in feces from children with gastroenteritis showed that HVR-derived genotypes IV and V occur in significantly higher numbers. In consequence, it may be concluded that the variability of the C-terminal nsP1a gene affects the virus replication phenotype.

Molecular epidemiology of astrovirus infection in Italian children with gastroenteritis

Abstract A 1-year study involving 157 gastroenteritis samples was conducted to investigate the role of human astrovirus (HAstV) as a cause of gastroenteritis in Italian children aged < 2 years. The overall incidence of HAstV was 3.1%. Most cases occurred between March and May, and four of the five isolates were of the HAstV-1 type, the other being HAstV-3. Analysis of genetic variability showed that the three HAstV-1 isolates collected in 2000 clustered together, but separately from the 1999 isolate. The results indicated that HAstV should be considered as a potential diarrhoeal pathogen in Italian children.

Diversity of enteric viruses detected in patients with gastroenteritis in a tertiary referral paediatric hospital

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.

Antigenicity of Two Turkey Astrovirus Isolates

Astroviruses are positive-sense single-stranded RNA viruses. These viruses cause gastroenteritis in humans and in a variety of animal species, including turkey poults. Only human astroviruses are well characterized antigenically. In the current study, two turkey astrovirus isolates, TAstV1987 and TAstV2001, were antigenically compared using cross-neutralization tests in turkey embryos, as well as cross-reactivity of the two isolates by an enzyme-linked immunosorbent assay (ELISA). The antigenic relatedness values (R) were calculated using the Archetti and Horsfall formula. The R value based on the cross-neutralization tests was 0.56%, which indicates that TAstV1987 and TAstV2001 belong to different serotypes; the R value of the two viruses based on ELISA was 70.7%, which suggests these two viruses share common antigen(s).

Astroviruses

Human astroviruses are members of the Astroviridae family. They are non-enveloped viruses possessing a single-stranded RNA of positive polarity as their genome. The development of sensitive tests for the presence of astrovirus-for example, using group reactive monoclonal antibodies-has led to the conclusion that astroviruses are the cause of more cases of childhood diarrhea. Astroviruses have also been identified as the cause of major outbreaks of diarrhea and vomiting. Different serotypes of human astrovirus have been defined based on immune electron microscopy, neutralization tests, and type-specific enzyme immune assays (EIAs). Eight different serotypes have been identified and it has been shown that differences in the sequences of reverse transcription-polymerase chain reactions (RT-PCR) products from a region within open reading frame 2 (ORF2) correlated precisely with antigenic types determined by type-specific EIA.

Asymptomatic and symptomatic excretion of noroviruses during a hospital outbreak of gastroenteritis

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.

Prevalence and genetic diversity of human astroviruses in Mexican children with symptomatic and asymptomatic infections

The prevalence and type diversity of human astroviruses (HAstV) in children with symptomatic and asymptomatic infections were determined in five localities of Mexico. HAstV were detected in 4.6 (24 of 522) and 2.6% (11 of 428) of children with and without diarrhea, respectively. Genotyping of the detected strains showed that at least seven (types 1 to 4 and 6 to 8) of the eight known HAstV types circulated in Mexico between October 1994 and March 1995. HAstV types 1 and 3 were the most prevalent in children with diarrhea, although they were not found in all localities studied. HAstV type 8 was found in Mexico City, Monterrey, and Mérida; in the last it was as prevalent (40%) as type 1 viruses, indicating that this astrovirus type is more common than previously recognized. A correlation between the HAstV infecting type and the presence or absence of diarrheic symptoms was not observed. Enteric adenoviruses were also studied, and they were found to be present in 2.3 (12 of 522) and 1.4% (6 of 428) of symptomatic and asymptomatic children, respectively.

Prevalence and characterization of astroviruses in Argentinean children with acute gastroenteritis

Among viral agents causing gastroenteritis, human astroviruses (HAstVs) take second or third place, after rotaviruses and caliciviruses, as the most frequent cause of illness. The aims of this study were to determine the prevalence of HAstV infection and to characterize the circulating HAstV strains in children with diarrhea under 3 years of age treated between 1995 and 1998 at out- or in-patient facilities of the children's hospital in Mendoza, Argentina. Reverse transcription-polymerase chain reaction (RT-PCR) and enzyme immunoassay (EIA) were used to detect HAstVs in stool specimens. Positive specimens were tested further by EIA and/or sequenced to type detected HAstV strains. HAstVs were detected in 40 (3.7%) of 1,070 samples that were rotavirus and calicivirus-negative: 14 (3.5%) of 402 from outpatients and 26 (3.9%) of 668 from inpatients. HAstV infection tended to be more severe in children during their first year of life: 18 (4.7%) of 383 HAstV-positive children 0-11 months old were hospitalized versus 8 (2.8%) of 285 children 1 year of age or older (P = 0.29). Type 1 (HAstV-1) was the most common type (41%), followed by HAstV-4 (25%), HAstV-2 (13%), HAstV-3 (13%), and HAstV-5 (8%). In this first epidemiological study of HAstV infection in this region, we confirmed HAstV to be a cause of severe gastroenteritis in children, more often among children younger than 12 months of age. HastV-4 caused 25% of HastV infections in Mendoza, although it has been detected commonly elsewhere. Distinct genetic lineages were apparent but their epidemiological significance remains to be demonstrated.

Molecular characterization and sequence analysis of human astroviruses circulating in Hungary

Human astroviruses (HAstVs) are major pathogens in viral gastroenteritis worldwide. Twenty-five HAstV strains were detected from stool specimens of children hospitalized for acute gastroenteritis in Budapest, Hungary, between 1995 and 1999. Sequence analysis was performed at the 3' end of the capsid gene to determine genotypic diversity of HAstVs circulating in Hungary. Five different genotypes of HAstVs were identified: HAstV-1 was predominant, followed by types 5, 8, 3 and 4. Two different subtypes of HAstV-1 were detected, but only one at a time in the community. This is the first report on the genetic diversity of HAstVs in Hungary and Central/Eastern Europe.

Persistent gastroenteritis in children infected with astrovirus: association with serotype-3 strains

The relationship between cases of persistent diarrhoea and the levels and type of human astrovirus was investigated. The potential correlation between human astrovirus excretion levels and the occurrence of protracted gastroenteritis was elucidated after quantifying astroviruses in faecal samples by a competitive RT-PCR. This assay was developed employing an internal RNA standard constructed for this purpose and showed a threshold of positivity of 3.4 x 10(4) genomes per gram of faeces. By this procedure, the levels of astrovirus, belonging to serotypes 1, 2, 3, 4, and 8, in faecal samples could be ascertained to range from 3.4 x 10(8) to 1 x 10(13) per gram of faeces. The mean viral titre in the serotype 3-containing faeces was higher than in any of the other serotype-containing samples. In children with no background disease, persistent gastroenteritis cases were detected in 8.5% of the astrovirus infections, and 37.5% of those were associated with astrovirus type 3 infection. In addition, 42.9% of astrovirus 3 isolates were implicated with persistent cases, some of them lasting for 3 months. Other type 3 isolates, detected in the faeces in very large numbers, caused severe gastroenteritis.

Viral agents of acute gastroenteritis in German children: prevalence and molecular diversity

Acute gastroenteritis is a major source of morbidity and mortality among young children in developed and developing countries. Enteropathogenic viruses are regarded as particularly relevant causative agents. Between February 2001 and January 2002, fecal specimens were obtained from German children admitted to hospital with acute gastroenteritis and examined for rotaviruses, Noroviruses, enteric adenoviruses, and astroviruses using (RT-)PCR methods. Of the 59% (129/217) samples positive for > or =1 viral agent, 79% (102/129) carried rotavirus, whereas Norovirus was detected in 35% (45/129), enteric adenovirus in 14% (18/129), and astrovirus in 4% (5/129). Thirty-eight specimens contained at least two enteropathogenic viruses, with the majority of coinfections attributable to rotavirus/Norovirus dual infections. Sequence analysis revealed a cocirculation of G1, G3, G4, and G9 type rotavirus with G1 being the most common and G9 the second most common rotavirus G-type. Emergence of G9 rotaviruses in Germany may have implications for future vaccine development. A variety of Norovirus genotypes, most belonging to GGII, were found. Apart from subgenus F, adenovirus related genetically to subgenera A-C were detected. All astroviruses belonged to genotype 1. This is the first study concerning German children admitted to hospital that assesses the relative importance of these viruses by nested (RT-) PCR methods.

Development of a rapid method using nucleic acid sequence-based amplification for the detection of astrovirus

We have developed a rapid method to detect astrovirus in fecal specimens utilizing nucleic acid sequence-based amplification (NASBA) and several detection methodologies, including a sandwich hybridization assay based on DNA-tagged liposomes (liposome-strip detection assay). RNA was extracted from 65 stool specimens that were positive for astrovirus by enzyme immunoassay and was amplified by both NASBA and reverse transcriptase PCR (RT-PCR). Also extracted and amplified were 19 specimens containing rotavirus, 20 specimens containing norovirus, five specimens containing adenovirus, 15 water negative control specimens, and eight specimens containing astrovirus reference strains. NASBA products were detected by electrochemiluminescence detection (ECL) and by liposome-strip detection; RT-PCR products were detected by ethidium bromide staining following gel electrophoresis and by liquid hybridization assay (LHA). There was no significant difference in the detection rates of NASBA- and RT-PCR-based assays, with one exception in which the NASBA/ECL assay detected astrovirus in eight specimens that tested negative by the RT-PCR/LHA assay. These results suggest that these NASBA-based detection methods have detection rates that are as good as or better than those of RT-PCR-based methods. Both NASBA and liposome-strip detection may be useful for field studies and environmental testing because these methods are rapid and do not require specialized equipment.

Viruses causing gastroenteritis

Acute gastroenteritis is one of the most common diseases in humans worldwide. Viruses are recognized as important causes of this disease, particularly in children. Since the Norwalk virus was identified as a cause of gastroenteritis, the number of viral agents associated with diarrheal disease in humans has steadily increased. Rotavirus is the most common cause of severe diarrhea in children under 5 years of age. Astrovirus, calicivirus and enteric adenovirus are also important etiologic agents of acute gastroenteritis. Other viruses, such as toroviruses, coronaviruses, picobirnaviruses and pestiviruses, are increasingly being identified as causative agents of diarrhea. In recent years, the availability of diagnostic tests, mainly immunoassays or molecular biology techniques, has increased our understanding of this group of viruses. The future development of a safe and highly effective vaccine against rotavirus could prevent, at least, cases of severe diarrhea and reduce mortality from this disease.

Molecular characterization of astroviruses by reverse transcriptase PCR and sequence analysis: comparison of clinical and environmental isolates from South Africa

A comparative analysis was performed with 25 isolates of astroviruses (AstVs) detected in sewage sources and 22 concurrently identified clinical AstV isolates from the Tshwane (Pretoria) Metropolitan Area in South Africa. The samples and specimens were screened for AstVs by using an enzyme immunoassay and/or a reverse transcriptase PCR (RT-PCR) for the highly conserved untranslated region (3' end) of the genome. The RT-PCR results were confirmed by oligonucleotide probe dot blot hybridization. Viable viruses were propagated in cell cultures for amplification when a minimal specimen was available or indeterminate sequences were obtained. AstV strains were characterized by RT-PCR and partial sequence analysis of the capsid region. The presence of multiple human AstV (HAstV) types in a single sewage sample complicated identification of individual strains, and additional type-specific RT-PCR and sequence analyses of the capsid region were required for characterization. Amplification and characterization of one genotype from a sample, therefore, did not preclude the possibility that a sample harbored additional different genotypes. Genotype and sequence information obtained from AstVs in wastewater samples were compared to information obtained from AstV strains from human stools. HAstV type 1 (HAstV-1), as well as HAstV-3, -5, -6, and -8, were identified among the clinical isolates, and HAstV-1, -2, -3, -4, -5, -7, and -8 were identified among the environmental samples. Phylogenetic analysis demonstrated that HAstV-1, -3, -5, and -8, which were present in human stool and sewage samples, clustered together, indicating that these viruses are closely related. The concurrent presence of identical HAstV strains in wastewater samples and in hospitalized patients suggests that AstVs present in the environment pose a potential risk to communities in which fecally contaminated water is used for recreational and domestic purposes.

Astrovirus acute gastroenteritis among children in Madrid, Spain

BACKGROUND

Human astroviruses cause infantile gastroenteritis worldwide, but the prevalence of disease varies greatly by setting. Since 1997 we have conducted a survey to determine the causes of diarrhea among Spanish children attending an emergency room in Madrid and to characterize the clinical features of viral-associated gastroenteritis.

OBJECTIVES

To define the epidemiologic role of astrovirus-associated gastroenteritis in Spanish children, to review its clinical features and to compare these illnesses with those caused by rotavirus. To assess the sensitivity of two methods of detection [enzyme-linked immunosorbent assay (EIA) and reverse transcriptase (RT)-PCR].

METHODS

Fecal specimens from 822 children with acute diarrhea treated at an emergency room were screened by EIA assays. Random astrovirus-positive samples were characterized by RT-PCR and nucleotide sequencing for their phylogenetic grouping.

RESULTS

Astrovirus was detected in 44 (5.3%) of 822 specimens tested by EIA. No pathogens were detected in fecal specimens from 238 (29%) children; however, in 137 of those with adequate remaining specimens, we found an additional 50 (6.1%) that were positive by RT-PCR. HAstV-1 was the most prevalent type followed by HAstV-2. The gastroenteritis associated with astrovirus alone was slightly less severe and had a lower score or risk of hospitalization than that associated with rotavirus (P < 0.05).

CONCLUSIONS

Astrovirus was found in 11.4% of all children whom we tested for enteric viral and bacterial pathogens, making it the second most common cause of acute gastroenteritis among Spanish children. True prevalence of astrovirus could be underestimated if only EIAs were used for detection.

Incidence of human astrovirus in central Australia (1995 to 1998) and comparison of deduced serotypes detected from 1981 to 1998

The incidence of astrovirus infection was determined among infants and young children admitted to Alice Springs Hospital (central Australia) with gastroenteritis from 1995 to 1998. Astrovirus was detected by reverse transcription-PCR in 33 of 495 stool samples, and this represented 4.3% of a total of 774 stool samples tested for astrovirus, rotavirus, and Norwalk-like viruses. Astrovirus incidence was substantially lower than that of rotavirus but higher than that of Norwalk-like viruses both overall and in each of the 4 years individually. Over the period from 1981 to 1998, including the period from 1981 to 1994 during which astrovirus was identified only by electron microscopy, astrovirus serotypes (deduced from genotypes) 1, 2, 3, and 4 were identified. Deduced serotypes 1, 3, and 4 all appeared regularly over this 18-year period. Also over this period, nucleotide variation (in some cases substantial) in a section of the capsid protein precursor region of the virus genome was evident among strains of all four of the deduced central Australian serotypes. Consequent amino acid changes were, however, only evident among deduced serotype 3 strains. Geographic variation at both the genome and the resultant amino acid levels was evident among strains of all four of the deduced central Australian serotypes and their respective prototypes isolated in the United Kingdom.

Sensitive detection of RNA viruses associated with gastroenteritis by a hanging-drop single-tube nested reverse transcription-PCR method

The detection of the human RNA viruses, calicivirus and astrovirus, requires high sensitivity and broad reactivity. A novel single-tube nested reverse transcription-PCR (RT-PCR) method is described here, in which all of the required reagents are included in the one tube; however, those required for the nested amplification are separated in a "hanging drop" in the cap to be introduced by centrifugation after the RT and first-round cDNA amplification steps. Broad reactivity was obtained by using primer cocktails covering the published sequence variation in the primer targets. The method was evaluated with clinical fecal samples from outbreak and sporadic cases. Norwalk-like virus types 1 and 2 and rotavirus were the causal agents in 10 of 12 outbreaks. A viral agent was detected in 44% of 197 samples from sporadic infections in patients presenting to community health centers and a children's hospital. Interestingly, whereas rotavirus was more common than astrovirus in patients presenting to the hospital (33 and 7.6%, respectively), the reverse was true for patients presenting to community health centers (4.2 and 34%, respectively).

Virus diversity in a winter epidemic of acute diarrhea in France

In France, an epidemic peak of acute diarrhea is observed each winter. Previous results suggested a viral etiology for these winter epidemics. We investigated the role of enteric viruses in acute diarrhea and their molecular diversity. One hundred sixty-one patients with acute diarrhea and 45 healthy patients (controls) from the general population were given a standardized questionnaire between December 1998 and May 1999. Stool specimens were screened for group A and C rotaviruses, human caliciviruses, astroviruses, and adenovirus types 40 and 41 by reverse transcription-PCR and/or enzyme immunoassay. Virologic analysis was positive for 63 cases (39%). Caliciviruses and group A rotaviruses were the most frequent (19 and 17% of cases, respectively). Two control stool specimens were found positive for group A rotavirus, and one was found positive for astrovirus. Molecular characterization of the strains disclosed a cocirculation of P[8],G1, P[8],G4, and P[4],G2 rotaviruses; type 1, 2, 3, 4, and 8 astroviruses; and Sapporo-like and Norwalk-like human caliciviruses. These four types of viruses accounted for an attributable risk of acute diarrhea of 34.7% for the general population, under the assumption of a causal role of these viruses.

Detection and characterisation of human astroviruses in children with acute gastroenteritis in Blantyre, Malawi

In a 2-year hospital-based study of paediatric gastroenteritis in Blantyre, Malawi, astroviruses were detected by enzyme immunoassay in 15 (1.9%) of 786 inpatients and in 9 (2.3%) of 400 outpatients. Greater disease severity was noted in children coinfected with human immunodeficiency virus (HIV). Six human astrovirus (HAstV) genotypes were identified, including HAstV-1 (25%), HAstV-2 (21%), HAstV-3 (25%), HAstV-4 (13%), HAstV-5 (4%), and HAstV-8 (13%). Although astroviruses are not major causes of gastroenteritis among children admitted to hospital in Blantyre, concomitant HIV infection appears to be a risk factor for increased severity of disease.

Molecular epidemiology of astrovirus infection in Barcelona, Spain

A 3-year study involving 2,347 gastroenteritis samples was conducted to determine the prevalence, time distribution, and medical significance of human astrovirus infection in Barcelona, Spain. The overall incidence of astrovirus was found to be 4.9%. Mixed infections with other enteric agents were detected in 17.2% of all astrovirus-positive samples. During the 3-year period, the highest astrovirus incidence was reported in the winter months, although infections also occurred in summer. The peak detection rate was observed in children between 2 and 4 years of age. Overall, HAstV-1 was the most prevalent type, followed by HAstV-4, HAstV-3, HAstV-8, and HAstV-2. HAstV-5, HAstV-6, and HAstV-7 were not detected during these 3 years. From our serotype data for each age group, we observed that HAstV-1, HAstV-2, and HAstV-3 affected mostly children younger than 3 years of age, while HAstV-4 and HAstV-8 had a greater impact in older children. Genetic variability was analyzed between astroviruses isolated in Barcelona and strains isolated in other parts of the world. A fourth lineage was described for HAstV-1, most likely due to the large number of assayed samples, which may also explain the high level of genetic variability observed in the astrovirus isolates.

An outbreak of gastroenteritis associated with astrovirus serotype 1 in a day care center, in Rio de Janeiro, Brazil

Between June 4th and June 20th 1996 rotavirus, adenovirus, and astrovirus (HAstrV) were investigated in fecal samples from 27 children under three years old with acute diarrhea, attending the Bertha Lutz day care center, in Rio de Janeiro. All fecal samples were analyzed by polyacrylamide gel electrophoresis (PAGE), reverse transcriptase polymerase chain reaction (RT-PCR), enzyme immunoassays (EIA), and electron microscopy (EM). Nine of them (33%) showed positive results for HAstrV by at least one of the employed methodologies. Eight were positive by RT-PCR and EIA, and six by EM. All positive samples were inoculated onto HT-29 (human colon adenocarcinoma) cultured cells for HAstrV isolation and seven were positive after three passages. The sequencing analysis of eight RT-PCR products (449 bp) from gene that codifies VP2 protein, showed a total nucleotide identity among them and 98% with HAstrV-1 (strain Oxford type 1). This is the first report of a gastroenteritis outbreak associated with HAstrv-1 in a day care center in Rio de Janeiro and it reinforces the importance of this virus in association with infantile acute gastroenteritis.

Characterisation of a South African human astrovirus as type 8 by antigenic and genetic analyses

Human astroviruses (HAstV) can, on the basis of immunoassays using type-specific rabbit antisera, be classified into eight serotypes that correlate with genotypes. Very few isolates of HAstV type 8 have been described and there is a paucity of data available with regard to the antigenic and genetic relationships between HAstV type 8 (HAstV-8) and HAstV types 1 (HAstV-1) to 7 (HAstV-7). A wild-type HAstV from a South African paediatric patient with diarrhoea was analysed antigenically, by immune electron microscopy and enzyme immunoassay, and genetically in selected regions of the ORF1a, ORF1b and ORF2 and characterised as a HAstV-8. This HAstV-8 strain exhibited greatest homology with HAstV-4 in the 5' end of the capsid gene and ORF1a and 1b, and greatest homology with HAstV-5 in the 3' end of the capsid region. This study confirms, by both antigenic and genetic analyses, that HAstV-8 represents a distinct antigenic and genotype and is the first report of a HAstV-8 from a hospitalised paediatric patient with diarrhoea in southern Africa.

Characterization of "Norwalk-like viruses" and astroviruses by liquid hybridization assay

"Norwalk-like viruses" (NLVs) and human astroviruses are causative agents of gastroenteritis in all age-groups. The typing of these agents is generally done by nucleotide sequencing, blot hybridization, or enzyme immunoassay. These techniques are expensive, time-consuming, and sometimes require scarce reagents, which limits the typing of NLVs and astroviruses to a few reference laboratories. This report describes a liquid hybridization assay that uses broadly reactive probes whose sequences are based on data from specimens in collections available at CDC and GenBank. Two astrovirus genogroup-specific probes were designed and tested successfully on 26 wild strains from all serotypes. Fourteen GII and 16 GI representative NLV strains were typed without cross-hybridization by using P1B- and P2A-specific probes, described previously, and new P2B- and P1A-specific probes. Analysis of the specificity of the probes, the effect of the mismatches during hybridization, and the sensitivity of hybridization assay demonstrates this method to be a rapid and simple technique for molecular typing of NLVs and preliminary characterization of astroviruses.

Ribovirus emergentes implicados en las gastroenteritis

Los virus se sitúan en un lugar preferente entre los agentes causales de diarrea aguda, en particular en la infancia. En este contexto el papel de los astrovirus, coronavirus, torovirus y picobirnavirus es emergente. Los astrovirus se han detectado en las heces entre el 1,2 y el 20 % de niños con diarrea que requieren atención médica en una gran variedad de localizaciones geográficas. Se han descrito brotes epidémicos en escuelas, guarderías y salas pediátricas, y son más frecuentes entre niños de menos de 3 años. En climas templados se ha demostrado una mayor incidencia invernal, y en climas tropicales ésta es similar en todo el año, siendo su transmisión preferente por vía orofecal. Se han reconocido siete serotipos de astrovirus humanos, de los cuales el más común es el uno. Los viriones pueden eliminarse durante amplios períodos y detectarse mediante microscopia electrónica. En estudios epidemiológicos se emplean técnicas de enzimoinmunoanálisis para detectar el antígeno común de grupo y se han desarrollado también técnicas basadas en la detección de ácidos nucleicos mediante hibridación y amplificación (reacción en cadena de la polimerasa).

Los coronavirus entéricos se han asociado con frecuencia con enfermedad gastrointestinal en recién nacidos y niños menores de 12 años. El papel de los torovirus y picobirnavirus como causa de gastroenteritis es también emergente. Se necesitan estudios epidemiológicos para determinar su verdadera frecuencia en la comunidad, identificar sus mecanismos de transmisión y explicar la fisiopatología de los cuadros provocados por estos agentes.

Molecular analysis of a serotype 8 human astrovirus genome

Human astroviruses are an important cause of gastroenteritis. As part of a molecular epidemiological study carried out in Mexico a human astrovirus isolate, Yuc-8, was adapted to grow in CaCo-2 cells, and its entire genome was sequenced. A 15 amino acid deletion in ORF1a, which has been associated with adaptation of astroviruses to grow in cells other than CaCo-2, was present in Yuc-8. Comparative sequence analysis of the Yuc-8 ORF2 with reported human astrovirus sequences revealed that this isolate belongs to genotype (serotype) 8. Two distinct domains in ORF2 were observed: an amino-terminal domain (residues 1 to 415), with identities higher than 81% among the strains analysed, and a carboxy-terminal domain (residues 416 to 782) with identities between 36 and 60%. Two non-superimposable phylogenetic trees were generated by separate analysis of these two domains, suggesting that a differential selective pressure is exerted along the structural polyprotein.

Identification and type distribution of astroviruses among children with gastroenteritis in Colombia and Venezuela

Astrovirus infections were detected by enzyme immunoassay in 12 (5%) of 251 stool samples from children with gastroenteritis from Bogota, Colombia. In addition, astroviruses were detected by reverse transcription-PCR in 3 (10%) of 29 stool samples negative for other enteric pathogens collected in Caracas, Venezuela, from children with gastroenteritis. Astrovirus type 1 was the most frequently detected virus.

RT-PCR identification and typing of astroviruses and Norwalk-like viruses in hospitalized patients with gastroenteritis: evidence of nosocomial infections

BACKGROUND

Astroviruses (HAstVs) and 'Norwalk-like viruses' (NLV) are frequent causes of gastroenteritis worldwide, though no data on the strains in circulation or their prevalence is available for France.

OBJECTIVES

We applied molecular methods to detect HAstVs and NLVs by reverse transcription-polymerase chain reaction (RT-PCR) in fecal samples collected during a 2-year period from children and adults hospitalized with gastroenteritis.

STUDY DESIGN

All samples negative for rotavirus and adenovirus by latex agglutination which contained small (25-40 nm) viral particles observed by electron microscopy (EM) were examined by RT-PCR. RT-PCR products were sequenced to characterize the HAstV and NLV strains present.

RESULTS

A total of 75 samples were analyzed by RT-PCR, of which 15 were positive for HAstV and 24 for NLV. Several distinct strains of serotype 1 HAstV, the predominant serotype, circulated during the period. Nineteen of the 24 NLVs were of the G2 genogroup including Mexico-like (n=10), Bristol-like (n=8), and Hawaii-like viruses (n=1); two were genogroup 1. Overall, seven (47%) of the 15 HAstV infections and nine (37.5%) of the 24 NLV infections appeared to be nosocomially acquired based on the date of admission in hospital and the date of illness.

CONCLUSION

This study provides additional evidence of the importance of nosocomial infections caused by NLV and HAstV.

Enteric virus infections and diarrhea in healthy and human immunodeficiency virus-infected children

Forty-three stool samples from 27 human immunodeficiency virus (HIV)-seropositive children and 38 samples from 38 HIV-negative children, collected during a 15-month period, were examined for enteric viruses. Diagnostic assays included enzyme immunoassays for rotavirus, adenovirus, and Norwalk virus; polyacrylamide gel electrophoresis for picobirnavirus and atypical rotavirus; and PCR for astrovirus and enterovirus. Specimens from HIV-positive children were more likely than those of HIV-negative children to have enterovirus (56 versus 21%; P < 0.0002) and astrovirus (12 versus 0%; P < 0.02), but not rotavirus (5 versus 8%; P > 0.5). No adenoviruses, picobirnaviruses, or Norwalk viruses were found. The rates of virus-associated diarrhea were similar among HIV-positive and HIV-negative children. Enteroviruses were excreted for up to 6 months in HIV-positive children; however, no evidence for prolonged excretion of poliovirus vaccine was observed. These results suggest that although infection with enterovirus and astrovirus may be frequent in HIV-infected children, enteric viruses are not associated with the diarrhea frequently suffered by these children.

Role of astroviruses in childhood diarrhea

Human astrovirus (HAstV) is a significant cause of acute diarrhea among children, resulting in outbreaks of diarrhea and occasionally in hospitalization. Improved detection methods for eight antigenic types of HAstV and studies assessing the frequency and severity of HAstV diarrhea have further defined the impact of HAstV infections in children. These studies have shown that HAstV infections are clinically milder (diarrhea, vomiting, fever) than rotavirus infections. However, frequent coinfection of HAstV with rotavirus and caliciviruses in childhood diarrhea complicates the epidemiology. Seroprevalence studies have provided evidence that the majority of children are infected by HAstV by 6 years of age. The route of transmission is probably fecal-oral from food or water sources. Recent and planned studies will help to define the epidemiology and in the future lead to prevention strategies, which could include vaccination.

Epidemiology of astrovirus infection in young children hospitalized with acute gastroenteritis in Melbourne, Australia, over a period of four consecutive years, 1995 to 1998

The incidence of astrovirus infection in children less than 5 years of age hospitalized with acute gastroenteritis in Melbourne, Australia, from 1995 to 1998 was determined. Astrovirus was detected in 40 of 449 specimens tested by Northern hybridization, and astrovirus infection was confirmed by reverse transcription-PCR with or without culture in CaCO-2 cells. This represented 3.0% (40 of 1, 327) of all children tested for enteric pathogens, including viral, bacterial, and parasitic pathogens, over the survey period. The incidences of astrovirus infection in each year were 4.4% (1995), 2. 2% (1996), 3.9% (1997), and 1.4% (1998). In 1995 and 1997, the incidences of astrovirus infection were greater than the incidence of infection with all individual bacterial pathogens and were either greater than or equal to the incidence of adenovirus infection. Astrovirus exhibited an unusual biennial winter peak of incidence that correlated with a greater incidence of serotype 1 virus and an increased rate of hospitalization of children aged 6 to 12 months. Uncommon (serotype 2 and 4) and rare (serotype 8) serotypes were detected during the survey period. Genetic analysis of ORF2 (which encodes the astrovirus capsid precursor) of Melbourne isolates showed nucleotide sequence variation from year to year. This was not accompanied by significant amino acid substitutions. However, geographical variation was apparent by comparison of Melbourne astrovirus isolates with prototype strains identified in the United Kingdom.

Detection of astrovirus gastroenteritis in children

A commercial enzyme immunoassay (EIA) for the detection of astrovirus antigen was used to detect the virus during a 12-month survey of enteric pathogens in children in outpatient (n = 238) and hospital (n = 176) settings. It was found to have a 100% sensitivity and 98.6% specificity. Nineteen astrovirus isolates were detected and confirmed by northern hybridization, cell culture, and RT-PCR. The virus was detected mainly amongst outpatients although a comparison of the detection rate with that in hospitalised children did not demonstrate a statistically significant difference (p = 0.1347). In contrast, there was a strong association between hospitalization and rotavirus infection (p = 0.0371), and a strong association between infection detected in outpatients and adenovirus infection (p = 0.0193). Strains of astrovirus were sequenced, genotyped and shown to be: type 1 (n = 11), type 3 (n = 1), and type 4 (n = 7). Maximum genetic variation in type 1 isolates was 8.6% and type 4 was 7.8%. Changes did not result in amino acid substitutions.

Infectious gastro-enteritis: an uncommon cause of diarrhoea in adult allogeneic and autologous stem cell transplant recipients

The incidence and aetiology of acute diarrhoea in 60 adult allogeneic or autologous stem cell transplant (SCT) recipients was determined in a prospective study. Stool specimens were obtained prior to SCT and on days +20, +40, +60 and +100 post transplant. Microbiological evaluation was performed for pathogenic bacteria, fungi, parasites and viruses. Forty-seven patients were evaluable of whom 31 had a total of 48 acute diarrhoeal episodes. Diarrhoea occurred in 79% of allogeneic and 47% of autologous SCT recipients (P < 0.05). Intestinal infections were found in three of 48 (6%) diarrhoeal episodes. Clostridium difficile with positive toxin was cultured twice and one stool specimen was positive for cryptosporidium. Intestinal pathogens were identified in 13 out of 172 stool specimens from asymptomatic patients and included: rotavirus (4), adenovirus (3), C. difficile, toxin positive (2), and others (4). Graft-versus-host disease was confirmed by biopsy in two of 36 episodes of diarrhoea in allogeneic patients, and in three patients a relationship between reactivation of cytomegalovirus and diarrhoea was suspected. In 40 of 48 (83%) episodes of diarrhoea no clear aetiology could be found.

Emerging and re-emerging infectious diseases

Microbial pathogens discovered as aetiological agents of human disease over the last 25 years are reviewed. Strengthening of laboratory and public health surveillance is of paramount importance for early detection and management of emerging infectious diseases.

Genetic variation in the capsid region of human astrovirus serotype 4 isolated in Japan

The entire capsid regions of 12 serotype-4 astroviruses from Japan were sequenced and compared with those of other serotypes. Serotype-4 isolates were divided into two new subgroups. The intrasubgroup nucleic acid and deduced amino acid sequences were quite homologous (more than 93%), but slightly less so between subgroups (almost 85%). However, the serotype-4 sequences differed from those of serotypes 1, 2, 3, 5, 6, 7 and 8 (less than 50%). Determining whether these differences significantly alter the epidemiology and antigenicity will require further investigation.

Absence of human astrovirus RNA in sewage and environmental samples

Over a period of several weeks during the summer of 1996, samples of sewage, sea water, river water, sand and silt were collected from a sewage works at Weston-super-Mare, England and from coastal areas nearby. A sensitive reverse-transcriptase polymerase chain reaction (RT-PCR) was used to search for human astrovirus (HAstV) RNA in concentrates of the samples. No evidence of astrovirus was found in any sample, which suggests that contamination with these viruses is not a problem in this area during the summer holiday season. Furthermore, the single case of astrovirus diarrhoea diagnosed in this laboratory in the summer occurred at the end of the sampling period, and not in the survey area. The primers used sometimes yielded a product two-thirds the expected size but bearing no sequence homology with HAstV. The confirmation that poliovirus adsorbs to sand and silt shows that these materials might be able to concentrate other enteric viruses in water to a level which could be a threat to the health of people coming into contact with it.