The Norovirus (NoVs), Caliciviridae family, is related with acute gastroenteritis (AGE) in people of all ages groups. Its importance as cause of outbreaks have been confirmed, which occur mainly indoors. Its transmission is mainly by the fecal-oral route through contaminated water and food, and person to person contact. The disease usually is characterized by diarrhea, vomiting, nausea and abdominal cramps. The aim of this study was to demonstrate the importance of NoVs as pathogen associated with hospital admissions of children with AGE in Belém, Pará. The collection of fecal specimens occurred from May 2008 to April 2011, being only tested the samples with negative results for rotavirus. The enzyme immunoassay (EIA) and the reverse transcription-polymerase chain reaction (RT-PCR) were used for NoVs detection. The samples with positive results by EIA and negative by RT-PCR, were submitted to the semi-nested RT-PCR, and the ones with remain negative, were tested by the real-time PCR. A total of 483 samples were analyzed with a positivity of 35.4% (171/483). Adopting the RT-PCR as the reference method, the EIA had a sensitivity of 85.9% and a specificity of 93.4% with excellent reproducibility between them (kappa = 0.8, p <0.0001). The 22 samples positive only by EIA were tested first by semi-nested RT-PCR and after by real-time PCR, with a positivity of 63.6% (14/22) and 75% (6/8), respectively. The partial nucleotide sequencing of ORF1 region demonstrated the presence of GII.4d (80.8%-42/52), GII.7 (7.7%-4/52) and GII.b (11.5%-6/52) genotypes. Sequencing was performed in 64.3% (9/14) of the samples positive only by semi-nested RT-PCR, also corresponding to ORF1, which 55.6% (5/9) were classified as GII.4d and 44.4% (4/9) as GII.b. Of the six samples classified as GII.b, five were characterized as GII.3 when sequenced with primers specifics for the capsid region, suggesting the possibility of recombinants samples. A higher infection rate was observed in children under 2 years of age (90.1%-154/171) and the main symptoms were vomiting (95.8%-137/143) and dehydration (94.4%-118/25), considering the diarrhea was an inclusion criterion. Most infected children had more than 9 days of diarrhea (41.2%), 4 evacuations per day (43.9%) and more than 5 episodes of vomiting (90%) during hospitalization. Regarding seasonality, three peaks of positivity were observed in September and October 2008 (63.6%), and in February 2010 (62.1%). Any correlation with the climatic parameters of rainfall, humidity and temperature was demonstrated. This study confirmed the importance of NoVs as viral enteropathogen associated with AGE among hospitalized children in Belém, imposing the necessity of an active surveillance, in order to avoid possible morbidity caused by this virus in childhood.
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