Tetravalent rhesus-human rotavirus vaccine (RRV-TV) in Belém, Brazil: efficacy against prevailing P and G genotypes.

To determine the efficacy of a reassortant rhesus-human tetravalent rotavirus vaccine (RRV-TV) (4 x 10(4) pfu/dose) against P and G rotavirus genotypes, 90 positive samples were tested using reverse transcription-polymerase chain reaction. The efficacy of the RRV-TV vaccine against P[8] and G1 individually or in binary combination P[8], G1 was 72 per cent (p < 0.005) 61 per cent (p < 0.013), and 70 per cent (p < 0.009), respectively, only for the first year of follow-up. In the second year, as well as after 2 years of follow-up, no efficacy was observed to these genotypes. These data indicate that further studies with rotavirus vaccines should focus on the molecular characterization of rotaviruses genotypes, in order to see whether or not cross-protection among different G and P genotypes may occur as a result of common bearing of VP4 specificities.

Detection and characterization of rotavirus G and P types from children participating in a rotavirus vaccine trial in Belém, Brazil.

This study sought the characterization of rotaviruses in a trial with a tetravalent rhesus-human rotavirus vaccine in Belém, Brazil in children who received three doses of vaccine or placebo in the 1st, 3rd and 5th months of life. Rotavirus electropherotypes, subgroups, G serotypes, G, [P] and [P], G genotypes were determined in 93.3%, 95.9%, 93.3%, 73.3%, 95.5% and 92.2% of isolates, respectively. Serotypes G1, G2 and G4 were detected in 58.9%, 30% and 4.4% of the cases, respectively. Rotavirus genotype G5 was detected for the first time in Northern region in 4.4% of the infections. Rotavirus genotypes P[8], P[4], P[6] and P[8 + 6] were detected in 54.5%, 26.7%, 12.2%, and 2.2% of the cases, respectively. The predominant genotypes were P[8], G1 and P[4], G2 with 53% and 26.6% of the infections, respectively. Unusual strains accounted for 20.5% including P[4], G1, P[6], G1, P[6], G4, P[6], G5, P[8], G2, P[8], G5. Mixed infections involving P[8 + 6], G2 and P[8 + 6], G1 were also noted. The neonatal P[6] strains associated with diarrhea were detected among children aged 9-24 months. To our knowledge, this study represents the first in Brazil to analyse, on molecular basis, rotavirus genotypes from children participating in a rotavirus vaccine trial. These results are of potential importance regarding future rotavirus vaccination strategies in Brazil.

Detection and characterization of Rotavirus G and P types from children participating in a Rotavirus vaccine trial in Belém, Brazil

This study sought the characterization of rotaviruses in a trial with a tetravalent rhesus-human rotavirus vaccine in Belém, Brazil in children who received three doses of vaccine or placebo in the 1st, 3rd and 5th months of life. Rotavirus electropherotypes, subgroups, G serotypes, G, [P] and [P],G genotypes were determined in 93.3 percent, 95.9 percent, 93.3 percent, 73.3 percent, 95.5 percent and 92.2 percent of isolates, respectively. Serotypes G1, G2 and G4 were detected in 58.9 percent, 30 percent and 4.4 percent of the cases, respectively. Rotavirus genotype G5 was detected for the first time in Northern region in 4.4 percent of the infections. Rotavirus genotypes P[8], P[4], P[6] and P[8+6] were detected in 54.5 percent, 26.7 percent, 12.2 percent, and 2.2 percent of the cases, respectively. The predominant genotypes were P[8],G1 and P[4],G2 with 53 percent and 26.6 percent of the infections, respectively. Unusual strains accounted for 20.5 percent including P[4],G1, P[6],G1, P[6],G4, P[6],G5, P[8],G2, P[8],G5. Mixed infections involving P[8+6],G2 and P[8+6],G1 were also noted. The neonatal P[6] strains associated with diarrhea were detected among children aged 9-24 months. To our knowledge, this study represents the first in Brazil to analyse, on molecular basis, rotavirus genotypes from children participating in a rotavirus vaccine trial. These results are of potential importance regarding future rotavirus vaccination strategies in Brazil

[Diagnosis of intestinal amebiasis using coproscopic and immunological methods in a population sample in greater metropolitan Belém, Pará, Brazil]. / Diagnóstico de amebíase intestinal utilizando métodos coproscópicos e imunológicos em amostra da população da área metropolitana de Belém, Pará, Brasil.

We compare diagnostic methods for Entamoeba histolytica in fecal samples from the city of Belém, Pará, Brazil. We analyze stool samples from children and adults (Group I); stool and serum samples from adults (Group II); and stool samples from children (Group III). In groups I and III, we used direct examination with lugol (DM), Faust et al (FM), and ELISA (detection of E. histolytica anti-GIAP coproantigen) and in group II, DM, iron hematoxylin staining (IHS), FM, ELISA, and the indirect immunofluorescence test (IFAT) for detection of IgG antibodies. Positivity was 10.50% by DM plus FM and 28.99% by ELISA. There was no correlation between positivity and age group. In Group II (n = 87), the positive rate was 4.59% by DM plus FM, 8.04% by IHS, 4.59% by IFAT, and 21.83% by ELISA. The ELISA test was the most sensitive for all groups. IFAT alone is still not a useful tool for diagnosis of E. histolytica infection. The ELISA test is simple, performed in one-third of cases used for IHS and IFAT, and greatly improves quality of diagnosis. We recommend this as the method of choice for diagnosis of suspected E. histolytica infection.

Reappraisal of the Peruvian and Brazilian lower titer tetravalent rhesus-human reassortant rotavirus vaccine efficacy trials: analysis by severity of diarrhea.

OBJECTIVES AND METHODS: With the purpose of better understanding the efficacy of the lower titer [4 x 10(4) plaque-forming units (pfu)] tetravalent rhesus-human reassortant rotavirus vaccine (RRV-TV) against diarrheal episodes of different severities, the Peruvian and Brazilian efficacy data were reanalyzed with a 20-point scoring system. Mild, moderate/severe and very severe rotavirus diarrhea were scored as 0 to 8, 9 to 14 and >14, respectively. RESULTS: In the Peruvian study one dose of vaccine yielded 64% (P = 0.04) protection against pure cases of rotavirus disease (i.e. those in which no other enteropathogen was found) with clinical scores ranging from 9 to 14. Protective efficacy against very severe rotavirus gastroenteritis could not be assessed because of the small number of cases. In Brazil there was a trend in preventing "all" and "pure" cases of rotavirus diarrhea scored 9 to 14 (44%, P = 0.06, and 45%, P = 0.08, respectively) and the vaccine was 75% (P = 0.02) protective against pure rotavirus diarrhea scored >14. No protection was observed for mild rotavirus diarrhea (scores <9). These data were compared with those from trials in Venezuela (4 x 10(5) pfu/dose), US (4 x 10(4) pfu/dose and 4 x 10(5) pfu/dose) and Finland (4 x 10(5) pfu/dose). Combining the Peruvian (one dose, pure cases) and Brazilian studies together, the levels of protection against 9- to 14-scored rotavirus diarrhea are comparable with those from the Venezuelan (47%) and American (57, 57 and 65%) efficacy trials. In Brazil the level of protection (75%) against pure, >14-scored rotavirus diarrhea is similar to the efficacy rates yielded in the three US trials (82, 80 and 69%) and the Finnish trial (100%) for episodes of the same severity. CONCLUSIONS: Our reanalysis provides evidence that, at least against moderate/severe rotavirus gastroenteritis, RRV-TV, 4 x 10(4) pfu/dose is potentially as efficacious as RRV-TV, 4 x 10(5) pfu/dose, even in settings with very high rotavirus disease burden. The reanalysis of the Peruvian data suggests that one and three vaccine doses may yield similar efficacy rates. It is also suggested that vaccine efficacy against most severe episodes in Peru and Brazil was not evident because of the trial design used in those studies (i.e. prospective, active home surveillance rather than a catchment trial), resulting in too few cases of severe disease even in the placebo group. To confirm these findings, future trials with this vaccine are necessary in developing countries with high diarrhea morbidity rates. These trials should use catchment designs and focus on the evaluation of the efficacy of one or three doses of RRV-TV against moderate to severe/very severe rotavirus diarrhea.

Rotavirus subgroups, G serotypes, and electrophoretypes in cases of nosocomial infantile diarrhoea in Belém, Brazil.

From November 1992 to November 1994 stool samples were obtained from 237 children admitted to a public hospital in Belém. Rotaviruses were detected in 19.3 per cent (60/310) of faecal samples. Of these, 32.1 per cent (18/56), 20.9 per cent (38/181), and 5.4 per cent (4/73) were recorded in cases of nosocomial diarrhoea, community-acquired diarrhoea, and controls, respectively. Fifty-two (86.7 per cent) of the 60 rotavirus-positive specimens were subgrouped and the G serotypes of 55 (91.7 per cent) of them were determined. Subgroups I and II were detected in 50 per cent each of the 52 subgrouped strains. G type 2 was present in 46 (83.6 per cent) of the 55 serotyped samples; serotypes G1 and (mixed) G1 and G4 were found in 14.5 per cent and 1.8 per cent, respectively, of these specimens. Viral RNA electrophoresis showed 14 distinct patterns, including 56.7 per cent (34/60) and 43.3 per cent (26/60) of long and short profiles, respectively. In 40 (66.6 per cent) of the 60 rotavirus-positive faecal samples no enteropathogens other than rotavirus were detected. There was an increased incidence of rotavirus infection from July 1993 to February 1994. The rotavirus-related episodes of diarrhoea were more severe than those of other aetiology and greater clinical severity was not related to a specific G type, subgroup, or electrophoretype.

An outbreak of group C rotavirus gastroenteritis among children attending a day-care centre in Belém, Brazil.

In August 1993, an outbreak of group C rotavirus-associated gastroenteritis occurred among children attending a day-care centre in Belém, Brazil. Of the 64 children, 21 (33%) became ill. Group C rotavirus was identified in faecal specimens from 8 (38%) children with diarrhoea by electron microscopy (EM) and an enzyme immunoassay (EIA), using antibodies specific to the Cowden strain of porcine group C rotavirus. By polyacrylamide gel electrophoresis (PAGE), a pattern similar to that of group C rotavirus was observed in 5 (62.5%) of the 8 EM- and EIA-positive samples. These 5 faecal samples were confirmed to be positive for group C rotavirus by reverse transcriptase-polymerase chain reaction, using specific VP6 and VP7 primers. This is the first report of an outbreak of diarrhoea in North Brazil associated with group C rotavirus. These findings suggest that group C rotavirus may be an important aetiological agent of diarrhoea in this region, which requires further study.

An outbreak of group C rotavirus gastroenteritis among adults living in Valentim Gentil, São Paulo State, Brazil.

An outbreak of gastroenteritis affecting adults and children occurred in the small city of Valentim Gentil, São Paulo, Brazil, in 1993. Nineteen faecal samples (from 10 cases and 9 contracts) were examined by direct electron microscopy (DEM), immune electron microscopy (IEM), polyacrylamide gel electrophoresis (PAGE), and enzyme-linked immunosorbent assay (ELISA) for group A and C rotaviruses. DEM detected rotavirus in 6 of the 10 cases and in none of the contacts. All of the samples were negative for group A rotavirus by ELISA. Analysis by PAGE showed an electrophoretic profile suggestive of group C rotavirus in two cases. Group C rotavirus was identified by IEM in 4 of the cases and in 1 of the contacts. All of the samples were submitted to ELISA for group C rotavirus. This resulted in a total of 10 positives-7 for diarrhoeal cases and 3 for contacts. This outbreak was strongly associated with group C rotavirus. The importance of combining different diagnostic methods is emphasised.

Rotavirus G and P types in children from Belém, northern Brazil, as determined by RT-PCR: occurrence of mixed P type infections.

Fifty-four group A rotavirus-positive stool samples, obtained from children aged less than three years during a longitudinal (December 1982 to March 1986) study in Belém, Brazil, were re-examined. The samples were tested by reverse-transcription and polymerase chain reaction to determine their G-type and P-type specificity. Only 17 (32%) of these rotavirus strains could be successfully G- and P-genotyped. While 10 (59%) of the 17 strains showed single G- and P-type specificity, the remaining belonged to single G- and mixed P-genotypes. Rotavirus strains P[8], G1 and P[4], G1 predominated, accounting for 29% and 18% of the typed strains respectively. Mixed P-type infections caused by rotaviruses classified as P[8] + P[4], G1 were identified in 23% of cases. All but 3 of the 54 rotavirus strains displayed long genomic profiles, as demonstrated by the analysis of RNA by polyacrylamide gel electrophoresis. Most (70%) rotavirus strains with single G- and P-type specificity were detected during the first year of life, whereas 5 (71%) of the seven mixed P-type infections occurred throughout the second or third year of age. Reinfections were noted in two children, both of them being infected with P[8] + P[4], G1 rotavirus strains when aged 20 months. The high proportion of untypeable rotavirus strains suggests that unusual types may be circulating in Belém. In addition, the occurrence of mixed P-type infections in our region indicates the potential for reassortment between different rotavirus genogroups. Monitoring of these rotavirus strains may have important implication in the context of future strategies of rotavirus vaccination in Brazil.

Inmunogenicidad, inocuidad y eficacia de una vacuna tetravalente obtenida por recombinación genética de rotavirus aislados de monos rhesus y seres humanos en Belém, Brasil / Immunogenicity, safety and efficacy of tetravalent rhesus-human, reassortant rotavirus vaccine in Belém, Brazil

Se evaluó la inocuidad, inmunogenicidad y eficacia de una vacuna tetravalente obtenida por recombinación genética de rotavirus aislados de monos rhesus y seres humanos (RRV-TV) (4 x 104 unidades formadoras de placas por dosis) en un ensayo prospectivo, aleatorio, a doble ciego y controlado con placebo que se efectuó con 540 lactantes brasileños. Se administraron dosis de vacuna o de placebo a la edad de 1, 3 y 5 meses. No se observaron diferencias significativas en la frecuencia de diarrea o vómito en los bebés de ninguno de los dos grupos después de administrar la dosis correspondiente. De 2 a 3% de los vacunados tuvieron fiebre baja los días tercero a quinto después de recibir la primera dosis, pero no después de las dosis segunda o tercera. Se observó una respuesta de anticuerpos del tipo IgA al rotavirus aislado de monos rhesus (RRV) en 58% de los vacunados y en 33% de quienes recibieron placebo. La respuesta de anticuerpos neutralizantes a cada serotipo no pasó de 20% cuando se determinó con la prueba de reducción de focos de fluorescencia, pero fue superior a 40% al medirse con la prueba de neutralización a base de reducción de placas. Se presentaron 91 casos de diarrea causada por rotavirus entre los niños que recibieron las tres dosis (de vacuna o de placebo) durante un seguimiento de 2 años, 36 de ellos en los niños vacunados. La eficacia general de la vacuna fue de 8% (P = 0,005) contra toda clase de diarrea y de 35% (P = 0,03) contra la diarrea causada por rotavirus. La protección durante el primer año de seguimiento, cuando predominó el rotavirus G del serotipo 1, fue de 57% (P = 0,008), pero se redujo a 12% en el segundo año. Se obtuvieron resultados similares al restringir el análisis a episodios en que el rotavirus fue el único agente patógeno identificado. Se observó en la vacuna una mayor tendencia a proteger contra casos de enfermedad con un promedio de seis o más deposiciones diarias. Estos resultados son lo suficientemente...

A tetravalent rhesus-human reassortant rotavirus (RRV-TV) vaccine (4 x 104 plaque-forming units/dose) was evaluated for safety, immunogenicity and efficacy in a prospective, randomized, double-blind, placebo-controlled trial involving 540 Brazilian infants. Doses of vaccine or placebo were given at ages, 1, 3 and 5 months. No significant differences were noted in the occurrence of diarrhoea or vomiting in vaccine and placebo recipients following each dose. Low-grade fever occurred on days 3­5 in 2­3% of vaccinees after the first dose, but not after the second or third doses of vaccine. An IgA antibody response to rhesus rotavirus (RRV) occurred in 58% of vaccinees and 33% of placebo recipients. Neutralizing antibody responses to individual serotypes did not exceed 20% when measured by fluorescent focus reduction, but exceeded 40% when assayed by plaque reduction neutralization. There were 91 cases of rotavirus diarrhoea among the 3-dose (vaccine or placebo) recipients during two years of follow-up, 36 of them among children given the vaccine. Overall vaccine efficacy was 8% (P = 0.005) against any diarrhoea and 35% (P = 0.03) against any rotavirus diarrhoea. Protection during the first year of follow-up, when G serotype 1 rotavirus predominated, was 57% (P = 0.008), but fell to 12% in the second year. Similar results were obtained when analysis was restricted to episodes in which rotavirus was the only identified pathogen. There was a tendency for enhanced protection by vaccine against illness associated with an average of 6 or more stools per day. These results are sufficiently encouraging to warrant further studies of this vaccine in developing countries using a higher dosage in an attempt to improve its immunogenicity and efficacy.

Concomitant rotavirus serotypes 1 and 4 infections in a diarrhoeic from Belem, Brazil

Infeccoes simultaneas por sorotipos 1 e 4 de rotavirus foram observadas em uma crianca de 15 meses de idade, do sexo feminino, internada com diarreia aguda contraida na comunidade que perdurou por 7 dias, evoluindo com desidratacao moderada. As evidencias dessas infeccoes foram inferidas baseadas em testes tais como: a) ensaio imunoenzimatico (ELISA), evidenciando-se reacao positiva para os sorotipos 1 e 4; e b) migracoes extras de segmentos de ARN visualizados a eletroforese em gel de poliacrilamida (EGPA). Esses resultados sugerem que as condicoes precarias de higiene e saneamento em que vivia essa crianca propiciam a infeccao macica por esses agentes virais. Alem disso, a co-circulacao de diferentes sorotipos no mesmo ambiente sustenta a necessidade de utilizar-se, no futuro, uma vacina polivalente, que proteja as criancas contra os quatro sorotipos G, epidemiologicamente importantes

Concomitant rotavirus serotypes 1 and 4 infections in a diarrhoeic child from Belém, Brazil.

Concomitant serotypes 1 and 4 infections were detected in a 15-month old female child with community-acquired diarrhoea which lasted 7 days and coursed with moderate dehydration. The evidence for dual rotavirus infection was offered by the following findings: a) enzyme-linked immunosorbent assay (ELISA) positive reactions to both 1 and 4 serotypes; and b) extra-migrating bands at electrophoresis of RNA in polyacrylamide gel (PAGE). These results suggest that children living under poor sanitation conditions are heavily exposed to rotavirus infections; in addition, the co-circulation of different serotypes in the same setting sustains the current concept that a rotavirus vaccine should be multivalent, in order to protect children against the four epidemiologically important rotavirus G serotypes.

Immunogenicity, safety and efficacy of tetravalent rhesus-human, reassortant rotavirus vaccine in Belém, Brazil.

A tetravalent rhesus-human reassortant rotavirus (RRV-TV) vaccine (4 x 10(4) plaque-forming units/dose) was evaluated for safety, immunogenicity and efficacy in a prospective, randomized, double-blind, placebo-controlled trial involving 540 Brazilian infants. Doses of vaccine or placebo were given at ages 1, 3 and 5 months. No significant differences were noted in the occurrence of diarrhoea or vomiting in vaccine and placebo recipients following each dose. Low-grade fever occurred on days 3-5 in 2-3% of vaccinees after the first dose, but not after the second or third doses of vaccine. An IgA antibody response to rhesus rotavirus (RRV) occurred in 58% of vaccinees and 33% of placebo recipients. Neutralizing antibody responses to individual serotypes did not exceed 20% when measured by fluorescent focus reduction, but exceeded 40% when assayed by plaque reduction neutralization. There were 91 cases of rotavirus diarrhoea among the 3-dose (vaccine or placebo) recipients during two years of follow-up, 36 of them among children given the vaccine. Overall vaccine efficacy was 8% (P = 0.005) against any diarrhoea and 35% (P = 0.03) against any rotavirus diarrhoea. Protection during the first year of follow-up, when G serotype 1 rotavirus predominated, was 57% (P = 0.008), but fell to 12% in the second year. Similar results were obtained when analysis was restricted to episodes in which rotavirus was the only identified pathogen. There was a tendency for enhanced protection by vaccine against illness associated with an average of 6 or more stools per day. These results are sufficiently encouraging to warrant further studies of this vaccine in developing countries using a higher dosage in an attempt to improve its immunogenicity and efficacy.

Rotaviruses as a cause of nosocomial, infantile diarrhoea in northern Brazil: pilot study.

Faecal samples were obtained from 190 children, aged 0 to 5 years, admitted to a public hospital in Belém, Pará, Brazil. These patients were placed in a pediatric ward with 40 beds distributed in six rooms. Cases were classified into three groups: (a) nosocomial: children who developed gastroenteritis 72 hr or later after admission; (b) community-acquired: patients admitted either with diarrhoea or who had diarrhoea within 72 hr following admission; (c) non-diarrhoeic: those children who had no diarrhoea three days before and three days after collection of formed faecal sample. Specimens were routinely processed for the presence of rotaviruses, bacteria and parasites. Rotaviruses were detected through enzyme-linked immunosorbent assay (ELISA) and subsequently serotyped/electrophoretyped. Rotaviruses were the most prevalent enteropathogens among nosocomial cases, accounting for 39% (9/23) of diarrhoeal episodes; on the other hand, rotaviruses occurred in 8.3% (11/133) and 9% (3/34) of community-acquired and non-diarrhoeic categories, respectively. Mixed infections involving rotavirus and Giardia intestinalis and rotavirus plus G. intestinalis and Entamoeba histolytica were detected in frequencies of 8.6 and 4.3%, respectively, in the nosocomial group. The absence of bacterial pathogens in this category, and the unusual low prevalence of these agents in the other two groups may reflect the early and routine administration of antibiotics following admission to this hospital. Rotavirus serotype 2 prevailed over the other types, accounting for 77.8% of isolates from nosocomial diarrhoeal episodes. In addition, at least five different genomic profiles could be observed, of which one displayed an unusual five-segment first RNA cluster. Dehydration was recorded in all cases of hospital-acquired, rotavirus-associated diarrhoea, whereas in only 57% of nosocomial cases of other aetiology. It was also noted that nosocomial, rotavirus-associated diarrhoeal episodes occur earlier (7 days), following admission, if compared with those hospital-acquired cases of other aetiology (14 days).

[Prospective study of rotavirus infections in Belém, Pará, Brazil: clinical and epidemiological features]. / Estudo prospectivo das infecções por rotavírus em Belém, Pará, Brasil: uma abordagem clínico-epidemiológica.

A prospective study of acute diarrhoeal diseases was carried out from April 1990 to September 1992 with the purpose of assessing the immunogenicity, safety and efficacy of a Rhesus-human reassortant rotavirus ("RRV-TV") vaccine, involving 540 children living in Belém, Pará, Brazil. As half of the children received placebo, this trial provided the opportunity of broadening the knowledge on both clinical and epidemiological aspects of rotavirus infection in the Amazon region. There were 2,789 diarrhoeal episodes during the above mentioned period, of which 86 (3.1%) associated with rotavirus; serotype 1 was the more prevalent, accounting for 67.9% of serotyped strains. Rates of 5.9 and 0.2 episodes of diarrhoea per child/year were noted for all cases and the rotavirus-related ones, respectively. This agent was the only pathogen found in 70.9% of the 86 rotavirus-related episodes of acute diarrhoea, whereas the most frequent associations involved Giardia intestinalis and enteropathogenic Escherichia coli, accounting for 7.0% and 11.6% of mixed infections,respectively. The monthly rates of rotavirus-related episodes of diarrhoea ranged from 0.8% to 9.6%, reaching the highest peaks during the dry months of the year. Means of clinical severity scores of 9.4 and 5.3 were recorded for the rotavirus-related episodes of diarrhoea and those of other aetiology, respectively.

Nosocomial transmission of an avian-like rotavirus strain among children in Belém, Brazil.

An atypical group-A rotavirus strain, with an electrophoretype displaying 5 segments in the first dsRNA size class, was detected among 3 hospitalized children less than 2 years old. Detection occurred initially 24 h after admission in a non-diarrhoeic child hospitalized because of acute respiratory infection. The second detection involved a child who occupied a different room within the same ward and who developed nosocomial diarrhoea 48 h later. A third case, also of hospital-acquired diarrhoea, was recorded in a child who occupied a bed in the same room as the second case and developed gastroenteritis 24 h following the second case's detection. In addition to the unusual, avian-like genomic profile, the strain was classified as serotype 2, based on a human VP7-specific enzyme-linked immunosorbent assay (ELISA). The question of whether these events reflect either a genomic rearrangement of a human rotavirus strain or a possible interspecies transmission will be further investigated through hybridization assays.

Prevalence of antibodies to Norwalk virus among Amerindians in isolated Amazonian communities.

The seroepidemiology of Norwalk virus infections was examined among Amerindians belonging to eight relatively isolated communities in the Amazon region by means of a new enzyme immunoassay using recombinant Norwalk virus antigen. The seroprevalence of antibodies to Norwalk virus ranged from 39% in the Maiogong to 100% in the Kubenkrankrein. The distribution of antibody levels varied greatly among groups; five of the eight communities had an antibody prevalence greater than 90% with many high values (> 100 units), while three had both a low seroprevalence and a preponderance of low values (< 100 units). While few children less than 5 years of age were sampled, no significant differences in antibody prevalence were noted among age groups, and the prevalence of antibody among children 5-10 years of age approached that of the older age groups. The low prevalence of titers of antibodies to Norwalk virus in several tribes living in these isolated Indian communities suggests that Norwalk virus may have been only recently introduced.