Viral load and genotypes of noroviruses in symptomatic and asymptomatic children in Southeastern Brazil

Background: Noroviruses (NoVs) are a major etiological agent of sporadic acute gastroenteritis worldwide. Objectives: To detect, quantify and characterize genogroups and genotypes of NoVs in children with and without gastrointestinal symptoms. Study design: NoVs were investigated by RT-PCR in a total of 319 fecal specimens from children up to three years old with (n = 229) and without (n = 90) acute diarrhea, between February 2003 and June 2004 in the emergency room in Vitoria, Southeastern Brazil. NoVs were quantified by real-time PCR and genotyped. Results: NoVs were detected in 17% (40/229) and 13% (12/90) of symptomatic and asymptomatic children, respectively. Six NoV-rotavirus A mixed infections were observed. Fifty-one strains were characterized as NoV GII and one as GI. Twenty strains were characterized as GII/4 (9/13), GII/3 (1/13), GII/6 (2/13) and GII/14 (1/13) in symptomatic and GII/3 (6/7) and GII/8 (1/7) in asymptomatic children. The median RNA viral loads were 8.39 and 7.15 log(10) copies/g of fecal specimens for symptomatic and asymptomatic children, respectively (p = 0.011). NoV load was lower when it was present in a mixed infection with rotavirus A (p = 0.0005). Conclusions: This study demonstrates a diversity of NoV strains circulating in this geographic area, and reports GII/8 and GII/14 in the American Continent for the first time. In addition, it confirms GII/4 as the most prevalent genotype in symptomatic children and identified GII/3 in an important frequency, especially in asymptomatic children. Furthermore, preliminary results show that symptomatic patients present a viral load that is significantly greater than asymptomatic children ( p = 0.011). (C) 2009 Elsevier B.V. All rights reserved.