Norovirus Gastroenteritis in a Birth Cohort in Southern India

Abstract

Background: Noroviruses are an important cause of gastroenteritis but little is known about disease and re-infection rates in community settings in Asia.

Methods: Disease, re-infection rates, strain prevalence and genetic susceptibility to noroviruses were investigated in a birth cohort of 373 Indian children followed up for three years. Stool samples from 1856 diarrheal episodes and 147 vomiting only episodes were screened for norovirus by RT-PCR. Norovirus positivity was correlated with clinical data, secretor status and ABO blood group.

Results: Of 1856 diarrheal episodes, 207 (11.2%) were associated with norovirus, of which 49(2.6%) were norovirus GI, 150(8.1%) norovirus GII, and 8 (0.4%) were mixed infections with both norovirus GI and GII. Of the 147 vomiting only episodes, 30 (20.4%) were positive for norovirus in stool, of which 7 (4.8%) were norovirus GI and 23 (15.6%) GII. At least a third of the children developed norovirus associated diarrhea, with the first episode at a median age of 5 and 8 months for norovirus GI and GII, respectively. Norovirus GI.3 and GII.4 were the predominant genotypes (40.3% and 53.0%) with strain diversity and change in the predominant sub-cluster over time observed among GII viruses. A second episode of norovirus gastroenteritis was documented in 44/174 (25.3%) ever-infected children. Children with the G428A homozygous mutation for inactivation of the FUT2 enzyme (se428se428) were at a significantly lower risk (48/190) of infection with norovirus (p = 0.01).

Conclusions: This is the first report of norovirus documenting disease, re-infection and genetic susceptibility in an Asian birth cohort. The high incidence and apparent lack of genogroupII specific immunity indicate the need for careful studies on further characterization of strains, asymptomatic infection and shedding and immune response to further our understanding of norovirus infection and disease.

Fig 1. Norovirus genotypes in primary and subsequent diarrheal episodes in children who had more than one infection.

Each line represents one child with re-infection, while the age in months is on the x- axis. Norovirus genotypes are represented by symbols. Samples that failed sequencing have been denoted as Failed in the figure. A) Children with re-infections with either norovirus GI and GII. B) All norovirus GI infection children who were re-infected with either GI or GII noroviruses. GI genotypes are shown, while GII infections are shown only as genogroup. C) All norovirus GII infection children who were re-infected with either GI or GII noroviruses. GII genotypes are shown while GI infections are shown only as genogroup.

Fig 2. Seasonal fluctuations in the monthly occurrence of episodes of norovirus-associated diarrhea.

The y-axis represents the monthly stool positivity rates (proportion of diarrheal episodes attributed to norovirus divided by the total number of diarrheal episodes). The x-axis represents the month of the year.

Fig 3

Proportion (with 95% CI) of (A) stunted, (B) wasted and (C) underweight children at 12, 24 and 36 months of age. The y-axis depicts the proportion of children with growth deficiency whereas the x-axis represents age in months. The point prevalence is presented as a circle and the 95% CI is represented as vertical lines. The solid vertical line represents uninfected children, the dashed and dotted lines represent those with single and multiple norovirus infections, respectively.

Fig 4. Dendrogram constructed using neighbor joining of nucleotide sequences corresponding to fragment of 468 bp of the ORF 1–2 region of the Norovirus capsid encoding gene.

Bootstrap values for 10000 pseudo replicates are shown. The reference strains included for comparison with accession numbers are: Hunter284/04/AU (DQ078794), Farmington Hills/02/US (AY502023), Sakai/04-179/05/JP (AB220922), Bristol/1993/UK (X76716), Maizuru/010426/2001/JP (EF547404), M7/1999/US (AY130761), Toronto/1991/CA (AAA18930), Seacroft/1990/UK (AJ277620), Hu/SaitamaU16/197/JP (AB039778), Erfurt546/2000/DE (AF427118), Mc37/2001/TH (AY237415), Wortley/1990/UK (AJ277618), Chitta/1996/JP (AB032758), Snow Mountain/1976/US (AY134748), Melksham/95/UK (X81879), KY-89/1989/JP (L23828), Norwalk/1968/US (M87661).