Comparative Clinical and Molecular Epidemiology of Norovirus in Hospitalized Gastroenteritis Cases, Western India (2013-2023).

Following widespread vaccination against Rotavirus A (RVA), Norovirus (NoV) has emerged as a leading cause of acute gastroenteritis (AGE). However, data on the clinical characteristics and molecular epidemiology of NoV in India remain limited. A total of 1637 fecal samples from hospitalized sporadic AGE cases collected between April 2013 and May 2023 from two cities each in Maharashtra and Gujarat, India, were screened for NoV. Positive samples were characterized by molecular genotyping. NoV was detected in 149 (9.1%) cases, with 123 (82.5%) infections occurring in children under 2 years of age. Most patients 103 (69.1%) had severe or very severe illness, and 22.8% had mixed viral infections, predominantly with RVA. Genotyping identified 11 VP1 genotypes, 9 RdRp P-types, and approximately 30 genotype combinations, demonstrating substantial genetic diversity. GII.4 (n = 66) and GII.P16 (n = 67) were the predominant variants and were associated with more severe disease than less common genotypes. The validated qRT-PCR assays demonstrated > 97% sensitivity and specificity for regional strains, enabling rapid and accurate diagnosis. The extensive genetic diversity of NoV circulating in Indian children highlights the need for enhanced molecular surveillance, improved diagnostics, and consideration of locally prevalent genotypes in future vaccine development.