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

Abstract 

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 Vitória, 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 7.15log₁₀copies/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).

Abbreviations: NoVs, noroviruses, ER, emergency room, nt, nucleotide, cDNA, complementary DNA, ORF, open reading frame

Keywords: Noroviruses, Symptomatic and asymptomatic children, Genogroup, Genotype, Viral load