Epidemiology of foodborne Norovirus outbreak in Incheon, Korea

Abstract

On June 14, 2008, an outbreak of gastroenteritis occurred among elementary school students in Incheon. We conducted an investigation to identify the source and described the extent of the outbreak. We performed a retrospective cohort study among students, teachers and food handlers exposed to canteen food in the elementary school. Using self-administered questionnaires we collected information on symptoms, days of canteen food eaten, food items consumed. Stool samples were collected from 131 symptomatic people and 11 food handlers. The catering kitchen was inspected and food samples were taken. Of the 1,560 people who ate canteen food, 117 were symptomatic cases, and the attack rate was 7.5%. Consumption of cucumber-crown daisy salad (RR=2.71), fresh cabbage mix (RR=2.23), dried radish salad (RR=3.04) and young radish kimchi (RR=2.52) were associated with illness. Sixty-four (45%) of the 142 stool specimens were positive for Norovirus. Norovirus was detected in 2 food handlers. Interviews with kitchen staff indicated the likelihood of contamination from an infected food handler to the dried radish salad during food processing. The excretion of Norovirus from asymptomatic food handlers may be an infection source of Norovirus outbreaks.

Keywords: Disease Outbreaks; Norovirus.

Fig. 1

The epidemic curve by symptom onset date, an elementary school, Incheon, Korea, 2008.

Fig. 2

Phylogenetic relationships between the outbreak strains and reference strains of NV based on partial nucleotide sequence of capsid. Nucleotide sequences were aligned using Clustal W and a phylogenetic tree was constructed by Neighbor-Joining method. The numbers on each branch indicate the bootstrap values for the clusters supported by that branch. Branch lengths are proportional to the calculated genetic distances (scale shown). FH A indicates the food handler A.