A new serotype of calicivirus associated with an outbreak of gastroenteritis in a residential home for the elderly

Norovirus Attachment and Entry

Human norovirus is a major human pathogen causing the majority of cases of viral gastroenteritis globally. Viral entry is the first step of the viral life cycle and is a significant determinant of cell tropism, host range, immune interactions, and pathogenesis. Bile salts and histo-blood group antigens are key mediators of norovirus entry; however, the molecular mechanisms by which these molecules promote infection and the identity of a potential human norovirus receptor remain unknown. Recently, there have been several important advances in norovirus entry biology including the identification of CD300lf as the receptor for murine norovirus and of the role of the minor capsid protein VP2 in viral genome release. Here, we will review the current understanding about norovirus attachment and entry and highlight important future directions.

Mechanism of Cell Culture Adaptation of an Enteric Calicivirus, the Porcine Sapovirus Cowden Strain

The porcine sapovirus (SaV) (PoSaV) Cowden strain is one of only a few culturable enteric caliciviruses. Compared to the wild-type (WT) PoSaV Cowden strain, tissue culture-adapted (TC) PoSaV has two conserved amino acid substitutions in the RNA-dependent RNA polymerase (RdRp) and six in the capsid protein (VP1). By using the reverse-genetics system, we identified that 4 amino acid substitutions in VP1 (residues 178, 289, 324, and 328), but not the substitutions in the RdRp region, were critical for the cell culture adaptation of the PoSaV Cowden strain. The other two substitutions in VP1 (residues 291 and 295) reduced virus replication in vitro. Three-dimensional (3D) structural analysis of VP1 showed that residue 178 was located near the dimer-dimer interface, which may affect VP1 assembly and oligomerization; residues 289, 291, 324, and 328 were located at protruding subdomain 2 (P2) of VP1, which may influence virus binding to cellular receptors; and residue 295 was located at the interface of two monomeric VP1 proteins, which may influence VP1 dimerization. Although reversion of the mutation at residue 291 or 295 from that of the TC strain to that of the WT reduced virus replication in vitro, it enhanced virus replication in vivo, and the revertants induced higher-level serum and mucosal antibody responses than those induced by the TC PoSaV Cowden strain. Our findings reveal the molecular basis for PoSaV adaptation to cell culture. These findings may provide new, critical information for the cell culture adaptation of other PoSaV strains and human SaVs or noroviruses.

IMPORTANCE

The tissue culture-adapted porcine sapovirus Cowden strain is one of only a few culturable enteric caliciviruses. We discovered that 4 amino acid substitutions in VP1 (residues 178, 289, 324, and 328) were critical for its adaptation to LLC-PK cells. Two substitutions in VP1 (residues 291 and 295) reduced virus replication in vitro but enhanced virus replication and induced higher-level serum and mucosal antibody responses in gnotobiotic pigs than those induced by the tissue culture-adapted strain. Structural modeling analysis of VP1 suggested that residue 178 may affect VP1 assembly and oligomerization; residues 289, 291, 324, and 328 may influence virus binding to cellular receptors; and residue 295 may influence VP1 dimerization. Our findings will provide new information for the cell culture adaptation of other sapoviruses and possibly noroviruses.

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.

Immunobiology of Norwalk virus

Clinical immunity to Norwalk virus in inoculated human volunteers appears to be unusual for gastroenteritis viruses, as certain individuals are repeatedly ill on long-term virus rechallenge and others remain persistently well. In these volunteers there is a paradoxical inverse correlation between the prechallenge serum (and jejunal fluid) Norwalk antibody level (measured by radioimmunoassay) and resistance to illness, suggesting that non-immunological factors, perhaps genetic, may be important in determining resistance. Most reported naturally occurring Norwalk disease outbreaks in developed nations also show that humoral antibody fails to correlate with immunity to infection. The unusual pattern of clinical immunity to Norwalk virus indicates a need for caution in the development of vaccines against this agent as well as a need for additional information on its immunobiological characteristics. The virus is known to contain a single protein, like the caliciviruses. Recently we have found evidence for at least a one-way serological cross-relatedness between Norwalk virus and human calicivirus. Twelve of 20 paired sera from ill patients in outbreaks due to calicivirus strain UK4 seroconverted to Norwalk virus by radioimmunoassay and two of eight paired sera from UK2 outbreaks showed seroconversion. Future studies of outbreaks caused by various calicivirus strains should be designed to correlate acute-phase serum antibody titres to Norwalk virus with clinical susceptibility and immunity to infection.

Characterization of sapoviruses collected in the United Kingdom from 1989 to 2004

A fecal archive containing 115 sapovirus (SaV) strains detected in samples collected from 15 outbreaks and 98 sporadic cases of gastroenteritis between 1989 and 2004 in the UK were characterized in order to determine the genomic diversity within SaV co-circulating in the human population. Strains were characterized by partial sequencing of the genes encoding the RNA-dependent RNA polymerase (RdRp) region and/or the polymerase/capsid (Pol/Cap) junction of the open reading frame (Orf) 1. Overall, SaV of genogroup I genotype 1 (GI 1) were the predominant strains circulating in the UK in each year between 1989 and 2004. During 2004, GII 1 was the predominant strain. These two SaV types accounted for 89.5% of the sporadic cases and outbreaks in the UK. The remaining cases were caused by six other SaV genotypes. On the basis of partial sequencing of the RdRp and capsid encoding genes of strains, which did not show sufficient homology to any of the currently recognized genotypes, we propose the inclusion of a presumptive fourth genotype within genogroup I (GI 4).

A predominant role for Norwalk-like viruses as agents of epidemic gastroenteritis in Maryland nursing homes for the elderly

Stool specimens from 156 Maryland nursing home residents, who became ill during 20 outbreaks of gastroenteritis from November 1987 through February 1988, were analyzed. All tested negative for astroviruses, enteroviruses, Group A rotaviruses, Sapporo-like caliciviruses, and enteric bacteria (i.e., Salmonella, Clostridium, and Shigella species). Eighty-two (52%) were positive for Norwalk-like viruses (NLVs), members of the family Caliciviridae. Six distinct genetic clusters within genogroups I and II of the NLVs were detected; a genogroup II (GII) virus closely related to the Camberwell virus in the NLV GII/4 genetic cluster was the predominant strain. Serologic evidence of infection with > or = 1 NLV was detected in 61 (56%) of 109 patients tested against 3 NLV antigens (i.e., Norwalk, Hawaii, and Toronto viruses). Sixteen (80%) outbreaks met the definition for an NLV outbreak. Taken together with a retrospective analysis of bacterial gastroenteritis in this same setting, these data support a major role for NLVs as etiologic agents of gastroenteritis in elderly persons.

Sapporo virus: history and recent findings

Morphologically distinct caliciviruses of human origin were first found in stools of children with gastroenteritis in 1976. Sapporo virus, or human calicivirus Sapporo, with typical surface morphology was first detected during a gastroenteritis outbreak in a home for infants in Sapporo, Japan, in 1977. Since then, morphologically and antigenically identical virus has been detected frequently in the same institution in association with outbreaks of gastroenteritis. Sapporo virus is widely distributed worldwide, as evidenced by the appearance of antigenically or genetically similar viruses and seroepidemiologic findings. Sapporo virus plays an important role in outbreaks of infantile gastroenteritis and is less important in foodborne outbreaks. Sapporo virus has been approved as the type species of the genus "Sapporo-like viruses in the family Caliciviridae. The history of and recent findings, as obtained by newly developed techniques, about Sapporo viruses are presented.

Design and evaluation of a primer pair that detects both Norwalk- and Sapporo-like caliciviruses by RT-PCR

A primer pair (p289/290) based on the RNA polymerase sequence of 25 prototype and currently circulating strains of human caliciviruses (HuCVs) was designed for the detection of both Norwalk-like caliciviruses (NLVs) and Sapporo-like caliciviruses (SLVs) by reverse transcription-polymerase chain reaction (RT-PCR). This primer pair produces RT-PCR products of 319 bp for NLVs and 331 bp for SLVs. The usefulness of this primer pair was shown by its detection of prototype NLVs (Norwalk, Snow Mountain, Hawaii and Mexico viruses) and SLVs (Sapporo/82, Hou/86, Hou/90 and Lon/92) and currently circulating strains of NLVs and SLVs in children and adults. This primer pair also detected more viruses in either NLV or SLV genera than previously designed primers. This primer pair is useful for broad detection of HuCVs for clinical and epidemiologic studies as well as for environmental monitoring.

Hospital-acquired infection in elderly patients

Increasing numbers of elderly people are being treated in hospitals and are at particular risk of acquiring infections. The incidence, risk factors and types of hospital-acquired infection (HAI) in the elderly are reviewed. Special reference is made to urinary tract infections, respiratory tract infections, gastrointestinal infections including Clostridium difficile, bacteraemia, skin and soft tissue infections and infections with antibiotic-resistant organisms.

Viral gastroenteritis: small round structured viruses, caliciviruses and astroviruses. Part II. The epidemiological perspective

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Measurement of IgA responses following Norwalk virus infection and other human caliciviruses using a recombinant Norwalk virus protein EIA

An enzyme immunoassay employing recombinant Norwalk virus capsid protein was evaluated for the measurement of IgA responses. Tests on 23 volunteers and patients known to have been infected with Norwalk virus (NV) showed that 19 developed significant IgA responses, 2 had unchanging levels of IgA and 2 failed to respond. There was no evidence of IgA responses to NV following infection with Hawaii or Snow Mountain-like viruses. Tests on sera from patients involved in outbreaks associated with eating contaminated shellfish suggest that some patients may have been infected with more than one strain of calicivirus. The use of the rNV EIA for measuring IgA and IgG responses in patients involved in a major outbreak of food poisoning affecting hospital staff indicated that the causative agent was probably NV.

Efficacy of a recombinant Norwalk virus protein enzyme immunoassay for the diagnosis of infections with Norwalk virus and other human "candidate" caliciviruses

A recombinant Norwalk virus antigen enzyme immunoassay (rNV EIA) for the detection fo Norwalk virus (NV) antibodies was evaluated using sera from volunteers and patients infected with Norwalk, Hawaii, Snow Mountain Agent, small round structured viruses (SRSV), and human calicivirus (HuCV) strains. The results for NV antibodies correlated well with previous results obtained using a NV radioimmunoassay. The test rNV EIA was found to be highly specific for NV. The results of tests on sera obtained from patients involved in confirmed outbreaks of SRSV in the UK showed that only 1/12 was due to Norwalk virus. Further evidence is presented that SRSV strain UK2 is antigenically related to NV.

Acute infectious diarrhea

Diarrhea continues to be a major cause of mortality and morbidity in third world countries as well as a major symptomatic complaint in the primary care setting in the United States. The etiologic pathogen depends on an exposure history to include recent travel to foreign countries, consuming fecally contaminated water or food, prior use of antibiotics, or homosexual behavior. A careful history from patients directed at attempting to identify particular risk factors may help in making a diagnosis. Not all patients require a diagnostic workup. A large number of patients may only require oral rehydration, careful observation over time with or without use of antimotility agents. In toxic appearing patients or patients with fever, however, bloody stools, abdominal pain or tenesmus, a selective diagnostic workup is indicated. Antimicrobial treatments are not always required, some pathogens clearly call for treatment while some have less clear indications and other pathogens are not responsive to antimicrobial agents at all. Finally, one needs to remember that the differential diagnosis of acute diarrhea includes many noninfectious origins.

Different stabilities to bile among feline calicivirus strains of respiratory and enteric origin

Feline calicivirus (FCV) strains isolated from feces (E-FCV) were compared with FCV strains of respiratory origin (R-FCV). All strains were shown to be labile at pH 3.0. All strains except one strain of E-FCV were found to be sensitive to the action of trypsin. When exposed to bile salt (deoxycholic acid sodium salt), all R-FCV strains were markedly inactivated, but none of the E-FCV strains was inactivated. It was possible to select bile-resistant substrains from a bile-sensitive strain.

Human viral gastroenteritis

During the last 15 years, several different groups of fastidious viruses that are responsible for a large proportion of acute viral gastroenteritis cases have been discovered by the electron microscopic examination of stool specimens. This disease is one of the most prevalent and serious clinical syndromes seen around the world, especially in children. Rotaviruses, in the family Reoviridae, and fastidious fecal adenoviruses account for much of the viral gastroenteritis in infants and young children, whereas the small caliciviruses and unclassified astroviruses, and possibly enteric coronaviruses, are responsible for significantly fewer cases overall. In addition to electron microscopy, enzyme immunoassays and other rapid antigen detection systems have been developed to detect rotaviruses and fastidious fecal adenoviruses in the stool specimens of both nonhospitalized patients and those hospitalized for dehydration and electrolyte imbalance. Experimental rotavirus vaccines have also been developed, due to the prevalence and seriousness of rotavirus infection. The small, unclassified Norwalk virus and morphologically similar viruses are responsible for large and small outbreaks of acute gastroenteritis in older children, adolescents, and adults. Hospitalization of older patients infected with these viruses is usually not required, and their laboratory diagnoses have been limited primarily to research laboratories.

Detection of human calicivirus antigen and antibody by enzyme-linked immunosorbent assays

Enzyme-linked immunosorbent assays (ELISAs) were developed to detect human calicivirus (HCV) antigen and antibody to HCV. The ELISAs were specific for HCV and as sensitive as a previously developed radioimmunoassay. These ELISAs were used to search for evidence of HCV infection in the United States, where HCV gastroenteritis has rarely been reported. One hundred sixty-three stool samples collected from children hospitalized with diarrhea were examined; one sample was positive in the ELISA. Typical calicivirus particles were found in this stool sample, and these particles reacted with a hyperimmune guinea pig anti-HCV serum by immune electron microscopy. The age-related acquisition of antibody to HCV in hospitalized infants and children (from birth to 19 years old) without gastroenteritis and in healthy adults was also evaluated. The pattern of acquisition of antibody to HCV was similar to that for group A rotaviruses, namely, beginning in infancy and becoming 100% by the age of 4 years. These data suggest that HCV is associated with infantile gastroenteritis in the United States, that infections with HCV are common, and that many infections with HCV (Sapporo strain) may not require hospitalization.

Serial propagation of porcine enteric calicivirus-like virus in primary porcine kidney cell cultures

A porcine enteric calicivirus-like virus was adapted to serial propagation in primary porcine kidney cell cultures. Attempts to propagate this virus in primary porcine kidney cells in the presence of trypsin or pancreatin or without medium supplementation were unsuccessful. A low-pH medium (pH 6.8) was also ineffective in virus propagation. Successful serial propagation of the virus required the presence of an intestinal-content preparation, derived from uninfected gnotobiotic pigs, in the cell culture medium. The best results were obtained with six-well plate cultures which were centrifuged after virus inoculation. Infected cells were detected by immunofluorescent staining of cell monolayers or detached cells which were harvested by centrifugation. Infected cells were first detected at passage 4 (1% infected cells), and infectivity increased with successive passages, with as many as 80% of the cells infected by passage 16. Extensive cytopathic effects were observed in inoculated cell cultures, but not in uninoculated control cell cultures, at each passage level after passage 13. The infected cells became separated, rounded, and detached, forming holes in the cell monolayer. Only virus particles exhibiting the six-pointed star appearance or stain-filled, cup-shaped depressions characteristic of caliciviruses were detected in inoculated cell culture supernatants by immune electron microscopy. Attempts to determine the titer of the virus by a cell culture immunofluorescence assay or plaque assay were unsuccessful.

The development and evaluation of radioimmune assays for the detection of immune globulins M and G against astrovirus

The development and evaluation of radioimmune assays for the detection of IgM and IgG antibodies to astrovirus are described. The test was shown to be sensitive and specific, and suitable for screening large numbers of sera. The use of the assays has established that astrovirus type 1 is prevalent in the United Kingdom and that not only infants but also schoolchildren and elderly patients are affected. Further evidence is given to support the view that Marin County Agent is antigenically related to astrovirus type 1.

Effect of age on viral infections: possible role of interferon

In both experimental animals and humans, three stages of susceptibility to viral infections are apparent: 1) the neonatal state, characterized by enhanced susceptibility to infections; 2) childhood and adolescence, during which there is decreased susceptibility; and 3) adulthood (sexual maturity), characterized by increased susceptibility to primary viral infections with advancing age. Moreover, advanced age is associated with reactivation of latent viruses, most notably VZV, and, most likely, oncogenic viruses as well. The mechanisms responsible for these alterations in susceptibility to viral infections have not been completely elucidated. Differences in antibody production do not seem to play a role. Most authors feel that depression of cell-mediated immunity, as measured by delayed cutaneous hypersensitivity or lymphocyte stimulation by mitogens and antigens may be of importance. There have been, however, only few studies on the role of antiviral moieties, such as the interferon(s). Our data on interferon formation in response to coxsackievirus B3 infection in mice suggest that adult mice produce relatively less interferon in relation to the amount of virus replicated in their tissues than do younger animals. Furthermore, the absolute amount of interferon produced by adult animals in response to intravenous injection of (non-replicating virus) NDV was less than that found in younger mice. We report our studies on interferon with no implication that these data supply an adequate explanation for the greater vulnerability of adult mice infected with coxsackievirus B3. It is unlikely that the matter of age and susceptibility has interferon (or indeed any other factor) as a single determinant.(ABSTRACT TRUNCATED AT 250 WORDS)

An outbreak of gastroenteritis in a home for the elderly associated with astrovirus type 1 and human calicivirus

We describe an outbreak of gastroenteritis, which lasted for 22 days in a residential home for the elderly. The outbreak was biphasic and affected 34/42 (80%) residents and 13/29 (44%) members of the staff. Calicivirus was associated with cases of illness during the first 9 days of the outbreak, and astrovirus type 1 with cases arising between days 16 to 22. Although the symptoms were generally mild, the resources required and the inconvenience caused were considerable.

Seroepidemiological survey of the prevalence of antibodies to a strain of human calicivirus

Batches of pooled immune globulins and sera were tested by immune electron microscopy (IEM) for the presence of antibodies to a strain of human calicivirus (HCV, UK1). The results show that this strain of HCV is prevalent throughout many parts of the world and that the majority of the population experience infection by the age of 12 years. The survey carried out in the United Kingdom indicates that the presence of maternal antibody correlates with some degree of protection during the first few weeks of life; the peak incidence of cases and acquisition of antibody occur between 3 months and 6 years. Tests on sera from Japan show a similar pattern of acquisition of antibodies and demonstrate that infection with more than one strain of HCV commonly occurs during childhood.

Is Clostridium difficile endemic in chronic-care facilities?

An apparent outbreak of Clostridium difficile diarrhoea on the chronic hospital ward of a long-term care facility prompted an investigation lasting seven months. Approximately a third of patients had stools that were positive for C difficile by either toxin or culture. Attempts to eradicate the infection by simultaneously treating all toxin-positive patients with metronidazole, limiting antibiotic use, and implementing enteric isolation were unsuccessful. New cases were both nosocomially acquired and imported into the facility. Of the C difficile toxin-positive patients, 34% had diarrhoea and 19/49 (38%) died during the study period. C difficile is not routinely sought by most clinical microbiology laboratories and may therefore be endemic in many long-term care facilities for the elderly.

Prevalence of antibody to human calicivirus in Japan and Southeast Asia determined by radioimmunoassay

Three hundred ninety single sera from adults in Japan, Indonesia, Singapore, and Papua New Guinea were tested for antibodies to human calicivirus (HCV) by a radioimmunoassay blocking test. A high prevalence of antibodies was observed in samples collected in Japan and Southeast Asia. Of 240 serum specimens collected from five districts in Japan, 209 (87.1%) were positive for HCV antibodies. No striking difference in the prevalence of the antibody was seen among those districts. In sera collected in Southeast Asia, 84.0% (126 of 150) had antibodies to HCV (70% [35 of 50] in Singapore, 88% [44 of 50] in Indonesia, and 94% [47 of 50] in Papua New Guinea). These results indicate that HCV is a common infectious agent in Japan and Southeast Asia.

Characterization of a new calicivirus isolated from feces of a dog

Canine calicivirus (CaCV), isolated from feces of a dog with diarrhea, was readily propagated in cultures of canine cells and in a dolphin cell line. Serologic evidence indicated many dogs in at least one geographic area had been infected with CaCV, but its role as an etiologic agent of disease was not established. In cell culture most CaCV virions were strongly cell-associated making purification difficult. CaCV was established as a member of the Caliciviridae by morphology and physicochemical properties of virions (density, sedimentation rate, single major polypeptide, RNA genome size), although some of the properties differed slightly from those of previously described caliciviruses; evidence was also obtained for caliciviral RNA species in infected cells. Based on tests with antisera to numerous caliciviruses and presumed caliciviruses, CaCV appeared to be not closely related to any previously described virus except the stunting syndrome agent of chickens.

Infections and infection risk in residents of long-term care facilities: a review of the literature, 1970-1984

We reviewed the English-language peer-reviewed journals and the Centers for Disease Control's Morbidity and Mortality Weekly Reports between 1970 and 1984 presenting information about infections and infection risk in residents of long-term care facilities. More than 50 articles met review criteria. Approximately one third of the articles were reports of outbreaks, primarily of respiratory and gastrointestinal infections. Seven articles reported rates for several infection sites, but most rates were not directly comparable to one another because numerators and/or denominators were different. Many of the studies have been done in Veterans Administration hospitals with largely male populations, which may limit their applicability to freestanding long-term care facilities with largely female clients. This review establishes the need for high-quality observational studies of infections in long-term care facilities. Such studies are needed before intervention studies can be done to measure the effect of manipulation of risk factors on infection outcome.

An outbreak of calicivirus associated gastroenteritis in an elderly persons home. A possible zoonosis?

An outbreak of gastroenteritis caused by calicivirus began amongst residents and staff of an old persons home 24 hours after the proprietor's dog had been sick. Serological evidence suggests that the calicivirus isolated from one of the cases may be capable of infecting dogs as well as man. The virus strain responsible for this outbreak differs antigenically from those associated with two other outbreaks in the U.K. and one in Japan. The characteristic morphology of calicivirus is lost if stool is stored at -70 degrees C.

Twelve-month surveillance of infections in institutionalized elderly men

Surveillance of infectious episodes in institutionalized elderly men permanently resident on two wards of a veterans' hospital was undertaken for a 12-month period. One-hundred eleven episodes were identified in 50 residents (74 per cent). The most frequent infections included lower respiratory tract infections (incidence 59/100 patient-years), febrile episodes with no source (43.4), skin and soft tissue infections (36.5), and gastroenteritis (33). Only pneumonia was associated with significant mortality. A specific etiologic agent was seldom identified other than for skin and soft tissue infections. Antimicrobial therapy was prescribed for 87 per cent of all infections. Ward staff absenteeism was associated with peak occurrences of infections in residents. Resident characteristics that correlated with infection were incontinence of bladder and of bowel. Mental status or degree of mobility did not correlate. While infections occur frequently in this population, mortality is common only with pneumonia. Infections occur more frequently in residents who have greater functional impairment.

The polypeptide of a human calicivirus

Viral particles morphologically resembling animals caliciviruses in the faeces of a patient with acute gastroenteritis were purified, radiolabeled with [125I], and analyzed by SDS-PAGE. A single major structural protein with a mol. mass 62,000 daltons was identified by immunoprecipitation technique. The finding is consistent with human calicivirus-like particles associated with gastroenteritis being a member of the family Caliciviridae.

Microtiter solid-phase radioimmunoassay for detection of human calicivirus in stools

A microtiter solid-phase radioimmunoassay (RIA) was developed for detection of human calicivirus in stool specimens. Seventy-eight stool specimens were tested by RIA. All 17 specimens positive for human calicivirus by electron microscopy (EM) were also positive by RIA. In addition, of 21 specimens obtained from an outbreak of caliciviral gastroenteritis, 11 were positive by RIA but negative by EM. Of 20 specimens positive for rotavirus by EM and 20 nondiarrheic specimens with no virus, 2 and 1, respectively, were positive by RIA but were subsequently shown to be falsely positive by a blocking test. There was no cross-reaction between human and feline caliciviruses. Thus, the test was more sensitive than EM and, with an appropriate blocking test, was specific for human calicivirus. It might be especially useful for screening large numbers of stool specimens.

Calicivirus gastroenteritis in North West London

During a thirty-month study of gastroenteritis in North West London, 592 cases were found to be associated with excretion of viruses. 39 (6·6%) of these patients, most of whom were admitted to hospital because of gastroenteritis, were shedding caliciviruses. The cases occurred throughout the year with a peak incidence in the winter. The 39 patients ranged in age from 6 weeks to 13 years, the peak incidence beig among infants aged 1-6 months. The clinical features of calcivirus infection are not distinguishable from those of rotavirus infection.