Occurrence of Norovirus GII.4 Sydney Variant-related Outbreaks in Korea

Human noroviruses are major causative agents of food and waterborne outbreaks of nonbacterial acute gastroenteritis. In this study, we report the epidemiological features of three outbreak cases of norovirus in Korea, and we describe the clinical symptoms and distribution of the causative genotypes. The incidence rates of the three outbreaks were 16.24% (326/2,007), 4.1% (27/656), and 16.8% (36/214), respectively. The patients in these three outbreaks were affected by acute gastroenteritis. These schools were provided unheated food from the same manufacturing company. Two genotypes (GII.3 and GII.4) of the norovirus were detected in these cases. Among them, major causative strains of GII.4 (Hu-jeju-47-2007KR-like) were identified in patients, food handlers, and groundwater from the manufacturing company of the unheated food. In the GII.4 (Hu-jeju-47-2007KR-like) strain of the norovirus, the nucleotide sequences were identical and identified as the GII.4 Sydney variant. Our data suggests that the combined epidemiological and laboratory results were closely related, and the causative pathogen was the GII.4 Sydney variant strain from contaminated groundwater.