Acute norovirus gastroenteritis in children in a highly rotavirus-vaccinated population in Northeast Brazil.

Background Gastroenteritis is one of the most important causes of morbidity and mortality in children and an important etiological agent is norovirus. Objective We describe the occurrence and characteristics of norovirus diarrhoea in children from Sergipe, Northeast-Brazil, over two consecutive periods of three years following rotavirus vaccine introduction. Study design A cross sectional hospital-based survey conducted from October-2006 to September-2009 and from July-2011 to January-2013. Acute diarrhoea cases had a stool sample collected and tested for norovirus by RT-PCR and positive samples were sequenced. Results In total 280 (19.6%) of 1432 samples were norovirus positive, including 204 (18.3%) of 1113 samples collected during the first period and 76 (23.9%) of 318 collected during the second period. The proportion of children with norovirus infection increased significantly through the second study period (χ2 for trend = 6.7; p = 0.009), was more frequent in rotavirus vaccinated and in younger children (p < 0.001). Of 280 norovirus-positive specimens, 188 (67.1%) were sequenced. Of these, 12 were genogroup I and 176 genogroup II. The main genotype was GII.4 (149/188, 79.3%), followed by GII.2 (6, 3.2%) and GII.6 (5, 2.6%). Conclusion Norovirus annual detection rates increased over the study period. The detection of norovirus was higher among young children