# Emergence of norovirus GII.17[P16] in adult patients with acute gastroenteritis in Thailand during 2021−2023

## TL;DR

The study found that a new strain of norovirus, GII.17[P16], became common in adult patients with stomach flu in Thailand from 2021 to 2023.

## Contribution

The emergence of norovirus GII.17[P16] in adult populations in Thailand is newly identified and characterized.

## Key findings

- Norovirus GII.17[P16] was the most frequently detected genotype among adult patients with acute gastroenteritis.
- GII.4 Sydney 2012[P31] had the highest viral load compared to other genotypes.
- The study provides insights into norovirus genotypes and their viral loads in Thailand.

## Abstract

Human norovirus is a major cause of acute gastroenteritis across all age groups. This study investigated the prevalence, genotypes, and viral loads of noroviruses in adult patients with acute gastroenteritis.

A hospital-based cross-sectional study was conducted between December 2021 and March 2023 in Thailand. The presence of noroviruses GI and GII in stool samples from patients with acute gastroenteritis were tested using RT-nested PCR and DNA sequencing. All norovirus GII-positive samples were further characterized by polymerase-capsid typing assay and semi-nested RT-PCR. Norovirus GII concentrations were determined by RT-qPCR.

Norovirus GII was detected in 11.2% (28/250) of stool samples. Genotyping of the VP1 and RdRp genes identified GII.4 Sydney 2012[P31], GII.17[P17], and GII.17[P16], with GII.17[P16] being the most frequently detected. Of 28 norovirus GII-positive samples, the most common genotype was GII.17 (35.7%), followed by GII.17[P16] (32.1%), GII.17[P17] (14.3%), GII.4 Den Haag (7.1%), and GII.4 Sydney 2012[P31], GII.3 and GII.2 (3.6% each). GII.4 Sydney[P31] infections had the highest viral load (8.3 × 109 genome copies/g), followed by GII.17[P17] (8.9 × 105 − 4.5 × 108 genome copies/g) and GII.17[P16] (3.7 × 104 − 1.6 × 107 genome copies/g). GII.3 (2.4 × 104 genome copies/g), GII.4 Den Haag (1.7 × 10⁴ and 3.8 × 10⁴ genome copies/g) and GII.17 (2.4 × 10³–7.4 × 10⁴ genome copies/g) exhibited lower viral concentrations.

These findings provide important epidemiological insights into norovirus circulation, highlighting the emergence of GII.17[P16] and informing future outbreak preparedness and vaccine development.